141 KiB
RETRO: a Modern, Pragmatic Forth
Welcome to RETRO, my personal take on the Forth language. This is a modern system primarily targetting desktop, mobile, and servers, though it can also be used on some larger (ARM, MIPS32) embedded systems.
The language is Forth. It is untyped, uses a stack to pass data between functions called words, and a dictionary which tracks the word names and data structures.
But it's not a traditional Forth. RETRO draws influences from many sources and takes a unique approach to the language.
RETRO has a large vocabulary of words. Keeping a copy of the Glossary on hand is highly recommended as you learn to use RETRO.
This book will hopefully help you develop a better understanding of RETRO and how it works.
The text in these files is Copyright (c) 2018-2020 by Charles Childers.
To the extent possible under law, Charles Childers has waived all copyright and related or neighboring rights to the RETRO Documentation. This work is published from: United States.
The historical papers are Copyright (c) 1999-2000 by Tom Novelli.
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Obtaining RETRO
Stable Releases
I periodically make stable releases. This will typically happen two to four times per year. These are good for those needing a solid base that doesn't change frequently.
Snapshots
A lot of development happens between releases. I make snapshots of my working source tree nightly (and often more often).
This is what I personally recommend for most users. It reflects my latest system and is normally reliable as it's used daily in production.
The latest snapshot can be downloaded from the following stable URLs:
- http://forthworks.com/retro/r/latest.tar.gz
- gopher://forthworks.com/9/retro/r/latest.tar.gz
Repository
I use a Fossil repository to manage development. To obtain a copy of the repository install Fossil and:
fossil clone http://forthworks.com:8000 retro.fossil
mkdir retro
cd retro
fossil open /path/to/retro.fossil
See the Fossil documentation for details on using Fossil to keep your local copy of the repository current.
This will let you stay current with my latest changes faster than the snapshots, but you may occasionally encounter bigger problems as some commits may be in a partially broken state.
If you have problems, check the version of Fossil you are using. I am currently using Fossil 2.10, you may experience issues checking out or cloning if using older versions.
Building on BSD, Linux, macOS, and outher Inix Targets
RETRO is well supported on BSD (tested on FreeBSD, NetBSD, OpenBSD), Linux, and macOS systems. It should build on any of these without issue.
Requirements
- c compiler & linker
- standard headers
- make
Process
For a standard 32-bit system:
Run make
For a 64-bit system:
Run make OPTIONS=-DBIT64
This will build the toolchain and then the main retro
executable.
Executables
In the bin/ directory:
retro
retro-unu
retro-muri
retro-extend
retro-embedimage
retro-describe
Platform Specific Notes
In addition to the 64-bit build, it is possible to override the image size, address stack depth, and data stack depth by defining the appropriate elements.
E.g., for a 64-bit build with:
4,000,000 cells of memory
4,000 item limit on data stack
500 item limit on address stack
Run make OPTIONS="-DBIT64 -DIMAGE_SIZE=4000000 -DSTACK_DEPTH=4000 -DADDRESSES=500"
Haiku
To build on Haiku, you need to link with the network library. E.g.:
make LDFLAGS=-lnetwork
Issues
If you run into any build issues, please send details to crc@forth.works so I can work on addressing them as quickly as possible.
Building RETRO on Windows
It is possible to build RETRO on Windows, though a few of the extensions are not supported:
- no
unix:words - no
gopher:words
This is currently more difficult than on a Unix host. If you have Windows 10 and WSL, it may be better to build under that (using the Unix instructions).
Setup Build Environment
RETRO on Windows is built with TCC.
Go to http://download.savannah.gnu.org/releases/tinycc/
Download the winapi-full and tcc-xxxx-bin packages for your system. Decompress them, copy the headers from the winapi package into the tcc directory.
Prepare Source
Copy the source/interfaces/retro-windows.c and the
source/interfaces/retro-windows.c to the directory you setup
tcc into.
Build
Building will require use of the command line. Assuming that tcc.exe is in the current directory along with the RETRO sources:
tcc retro-windows.c -o retro.exe
Building Alternative Systems
In addition to the C implementation, there are a few other interfaces that can be built.
Requirements
- c compiler (tested: clang, tcc, gcc)
- make
- standard unix shell
retro-repl
A basic interactive system can be built by using:
make bin/retro-repl
This requires a copy of ngaImage to be in the current
directory.
Barebones
This is a minimal version of the retro-repl. It keeps the C
portion as short as possible, making it a useful starting point
for new interfaces.
To build:
make bin/retro-barebones
retro-compiler
This is a turnkey compiler. It can compile a new executable bundling a Retro VM and image.
Requirements:
- BSD or Linux
- objcopy in $PATH
To build:
make bin/retro-compiler
Example use:
-
Given a source file like "Hello.forth":
:hello 'hello_world! s:put nl ; -
Use:
./bin/retro-compiler Hello.forth hello
The first argument is the source file, the second is the word to run on startup.
- Run the generated
a.out
Limits:
This only supports the core words ('all' interface) and the file i/o words. Support for other I/O extensions will be added in the future.
Pascal
There is a Pascal version of retro-repl.
Dependencies:
- freepascal
Building:
cd vm/nga-pascal
fpc listener.lpr
This will require a copy of the ngaImage in the
current directory.
Python: retro.py
This is an implementation of retro-repl in Python. As
with retro-repl it requires the ngaImage in the current
directory when starting.
C#: retro.cs
This is an implementation of retro-repl in C#. As with
retro-repl it requires the ngaImage in the current
directory when starting.
Building:
cd vm\nga-csharp
csc retro.cs
You'll need to make sure your path has the CSC.EXE in it, or provide a full path to it. Something like this should reveal the path to use:
dir /s %WINDIR%\CSC.EXE
I've only tested building this using Microsoft's .NET tools. It should also build and run under Mono.
Advanced Builds
Custom Image
For users of BSD, Linux, macOS, you can customize the image at build time.
In the top level directory is a package directory containing
a file named list.forth. You can add files to compile into
your system by adding them to the list.forth and rebuilding.
Example:
If you have wanted to include the NumbersWithoutPrefixes.forth example, add:
~~~
'example/NumbersWithoutPrefixes.forth include
~~~
To the start of the list.forth file and then run make again.
The newly built bin/retro will now include your additions.
Starting RETRO
RETRO can be run for scripting or interactive use.
Interactive
To start it interactively, run: retro without any command line
arguments, or with -i, -s, or -i,c.
Starting the interactive system:
retro
Or:
retro -i
This should be sufficient for most uses.
Starting the interactive system (without displaying the startup banner):
retro -s
Using In a Pipe
If using a Unix shell and piping input between processes, you
will probably want to use -s to supress the startup messages
and Ok prompt that normally appear.
E.g.,
echo "'lol s:put nl" | retro -s
Running A Program In A File
You can run code in a file very easily. This is simply:
retro filename
You can follow the filename with any arguments that it may need.
These will be accessible to the program via the sys:argc and
sys:argv words.
Source files must be written in Unu format.
Scripting
You can use RETRO to write scripts. Add a shebang:
#!/usr/bin/env retro
And make the file executable.
Source files must be written in Unu format.
Command Line Arguments
For a summary of the full command line arguments available:
Scripting Usage:
retro filename [script arguments...]
Interactive Usage:
retro [-h] [-i] [-c] [-s] [-f filename] [-t]
-h Display this help text
-i Interactive mode (line buffered)
-s Suppress the startup text
-f filename Run the contents of the specified file
-t Run tests (in ``` blocks) in any loaded files
Basic Interactions
Start RETRO in interactive mode:
retro -i
You should see something similar to this:
RETRO 12 (rx-2019.6)
8388608 MAX, TIB @ 1025, Heap @ 9374
At this point you are at the listener, which reads and processes your input. You are now set to begin exploring RETRO.
To exit, run bye:
bye
Unu: Simple, Literate Source Files
RETRO is written in a literate style. Most of the sources are in a format called Unu. This allows easy mixing of commentary and code blocks, making it simple to document the code.
As an example,
# Determine The Average Word Name Length
To determine the average length of a word name two values
are needed. First, the total length of all names in the
Dictionary:
~~~
#0 [ d:name s:length + ] d:for-each
~~~
And then the number of words in the Dictionary:
~~~
#0 [ drop n:inc ] d:for-each
~~~
With these, a simple division is all that's left.
~~~
/
~~~
Finally, display the results:
~~~
'Average_name_length:_%n\n s:format s:put
~~~
This illustrates the format. Only code in the fenced blocks (between ~~~ pairs) get extracted and run.
(Note: this only applies to source files; fences are not used when entering code interactively).
On The Name
The name Unu comes from the Maori language, where it means:
(verb) (-hia) pull out, withdraw, draw out, extract.
Taken from https://maoridictionary.co.nz/
A Quick Tutorial
Programming in RETRO is all about creating words to solve the problem at hand. Words operate on data, which can be kept in memory or on the stack.
Let's look at this by solving a small problem: writing a word to determine if a string is a palindrome.
A palindrome is a phrase which reads the same backward and forward.
We first need a string to look at. Starting with something easy:
'anna
Looking in the Glossary, there is a s:reverse word for
reversing a string. We can find dup to copy a value, and
s:eq? to compare two strings. So testing:
'anna dup s:reverse s:eq?
This yields -1 (TRUE) as expected. So we can easily
name it:
:palindrome? dup s:reverse s:eq? ;
Naming uses the : prefix to add a new word to the dictionary.
The words that make up the definition are then placed, with a
final word (;) ending the definition. We can then use this:
'anna palindrome?
Once defined there is no difference between our new word and any of the words already provided by the RETRO system.
Syntax
RETRO has more syntax than a traditional Forth due to ideas borrowed from ColorForth and some design decisions. This has some useful traits, and helps to make the language more consistent.
Tokens
Input is divided into a series of whitespace delimited tokens. Each of these is then processed individually. There are no parsing words in RETRO.
Tokens may have a single character prefix, which RETRO will use to decide how to process the token.
Prefixes
Prefixes are single characters added to the start of a token to guide the compiler. The use of these is a major way in which RETRO differs from traditional Forth.
When a token is passed to interpret, RETRO first takes the
intitial character and looks to see if there is a word that
matches this. If so, it will pass the rest of the token to
that word to handle.
In a traditional Forth, the interpret process is something like:
get token
is token in the dictionary?
yes:
is it immediate?
yes: call the word.
no: are we interpreting?
yes: call the word
no: compile a call to the word
no:
is it a number?
yes: are we interpreting?
yes: push the number to the stack
no: compile the number as a literal
no: report an error ("not found")
In RETRO, the interpret process is basically:
get token
does the first character match a `prefix:` word?
yes: pass the token to the prefix handler
no: is token a word in the dictionary?
yes: push the XT to the stack and call the
class handler
no: report an error ("not found")
All of the actual logic for how to deal with tokens is moved to the individual prefix handlers, and the logic for handling words is moved to word class handlers.
This means that prefixes are used for a lot of things. Numbers?
Handled by a # prefix. Strings? Use the ' prefix. Comments?
Use (. Making a new word? Use the : prefix.
The major prefixes are:
| Prefix | Used For |
| ------ | ----------------------------- |
| @ | Fetch from variable |
| ! | Store into variable |
| & | Pointer to named item |
| # | Numbers |
| $ | ASCII characters |
| ' | Strings |
| ( | Comments |
| : | Define a word |
The individual prefixes will be covered in more detail in the later chapters on working with different data types.
Word Classes
Word classes are words which take a pointer and do something with it. These are covered in detail in their own chapter, but essentially they decide how to execute or compile specific types of words.
Additional Tools
In addition to the core retro binary, the bin directory
will contain a few other tools.
retro
This is the main RETRO binary.
retro-describe
This is a program that looks up entries in the Glossary.
At the command line, you can use it like:
retro-describe s:for-each
You can pass multiple word names to it:
retro-describe s:for-each nl d:words
retro-embedimage
This is a program which generates a C file with the ngaImage
contents. It's used when building retro.
retro-embedimage ngaImage
The output is written to stdout; redirect it as needed.
retro-extend
This is a program which compiles code into the ngaImage.
It's used when building retro and when you want to make a
standalone image with custom additions.
Example command line:
retro-extend ngaImage example/rot13.forth
Pass the image name as the first argument, and then file names as susequent ones. Do not use this for things relying on I/O apart from the basic console output as it doesn't emulate other devices. If you need to load in things that rely on using the optional I/O devices, see the Advanced Builds chapter.
retro-muri
This is the assembler for Nga. It's used to build the initial RETRO kernel and can be used by other tools as well.
retro-muri rx.muri
retro-tags and retro-locate
These tools are intended to be used together. The first tool,
retro-tags, will recursively scan the current directory for
RETRO source files and extract the locations of words defined
in them. These will be written to disk in a tags file, using
the standard ctags format.
retro-locate takes a word name, and returns the location(s)
where it is defined. This requires a tags file to be present.
Create the tags file:
retro-tags
Locate a word:
retro-locate n:square
retro-unu
This is the literate source extraction tool for RETRO. It
is used in building retro.
Example usage:
retro-unu literate/RetroForth.md
Output is written to stdout; redirect as neeeded.
The Optional Retro Compiler
In addition to the base system, users of RETRO on Unix hosts
with ELF executables can build and use the retro-compiler
to generate turnkey executables.
Requirements
- Unix host
- ELF executable support
objcpyin the $PATH
Building
BSD users:
make bin/retro-compiler
Linux users:
make -f Makefile.linux bin/retro-compiler
Installing
Copy bin/retro-compiler to somewhere in your $PATH.
Using
retro-compiler takes two arguments: the source file to
compile and the name of the word to use as the main entry
point.
Example:
Given a hello.forth:
~~~
:hello 'Hello_World! s:put nl ;
~~~
Use:
retro-compiler hello.forth hello
The compiler will generate an a.out file which you can
then rename.
Known Limitations
This does not provide the scripting support for command line
arguments that the standard retro interface offers.
A copy of objcopy needs to be in the path for compilation
to work.
The current working directory must be writable.
This only supports hosts using ELF executables.
The output file name is fixed to a.out.
RETRO(1) General Commands Manual RETRO(1)
RETRO retro - a modern, pragmatic forth development system
SYNOPSIS retro [-h] [-i] [-t] [-f filename] [-u filename] [-r filename] [filename script-args]
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro is the main interface for interacting with Retro. It provides both
an interactive and a scripting model.
OPTIONS -h Display a help screen.
-i Start Retro in interactive mode.
-s Start Retro in interactive mode and supress the startup message.
-t Run any test blocks in the loaded files.
-f filename
Run any code blocks in the specified file.
-u filename
Load and use the specified image file rather than the integral
one.
-r filename
Load and run the code in the specified image file rather than
the integral one.
filename script-args
Run code blocks in a single file. Pass script-args to the code
being run.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 Setember 2019 OpenBSD 6.4
RETRO-DESCRIBE(1) General Commands Manual RETRO-DESCRIBE(1)
RETRO-DESCRIBE retro-describe - a modern, pragmatic forth development system
SYNOPSIS retro-describe wordname [additional wordnames]
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-describe is a tool for looking up the description and stack
comments for words in the core language and extensions. It will write
output to stdout.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 May 2019 OpenBSD 6.4
RETRO-DOCUMENT(1) General Commands Manual RETRO-DOCUMENT(1)
RETRO-DOCUMENT retro-document - a modern, pragmatic forth development system
SYNOPSIS retro-document filename
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-document is a tool for generating a listing of the descriptions and
stack comments for all standard word used in a source file. It will write
output to stdout.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 May 2019 OpenBSD 6.4
RETRO-EMBEDIMAGE(1) General Commands Manual RETRO-EMBEDIMAGE(1)
RETRO-EMBEDIMAGE retro-embedimage - a modern, pragmatic forth development system
SYNOPSIS retro-embedimage [filename]
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-embedimage loads the specified image (or `ngaImage` from the
current directory if none is specified). It converts this into C code
that can be compiled for inclusion in a RETRO executable. It will write
the output to stdout.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 February 2019 OpenBSD 6.4
RETRO-EXTEND(1) General Commands Manual RETRO-EXTEND(1)
RETRO-EXTEND retro-extend - a modern, pragmatic forth development system
SYNOPSIS retro-extend image filename [filenames]
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-extend is a tool to load additional code into an image file. It
takes the name of an image file and one or more source files to load into
the image. After completion the image file will be updated with the
changes.
CAVETS retro-extend only emulates the minimal console output device. If the source files require additional I/O to be present, the extend process will likely fail to work correctly.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 February 2019 OpenBSD 6.4
RETRO-LOCATE(1) General Commands Manual RETRO-LOCATE(1)
RETRO-LOCATE retro-locate - a modern, pragmatic forth development system
SYNOPSIS retro-locate wordname
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-locate searches the tags file generated by retro-tags for the
desired word name. Any matches are displayed, along with the line number.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.6 January 2020 OpenBSD 6.6
RETRO-MURI(1) General Commands Manual RETRO-MURI(1)
RETRO-MURI retro-muri - a modern, pragmatic forth development system
SYNOPSIS retro-muri filename
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-muri is an assembler for Nga, the virtual machine at the heart of
Retro. It is used to build the image file containing the actual Retro
language.
This will extract the code blocks in the specified file and generate an
image file named `ngaImage`.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 February 2019 OpenBSD 6.4
RETRO-TAGS(1) General Commands Manual RETRO-TAGS(1)
RETRO-TAGS retro-tags - a modern, pragmatic forth development system
SYNOPSIS retro-tags
DESCRIPTION RETRO is a modern, pragmatic Forth drawing influences from many sources. It's clean, elegant, tiny, and easy to grasp and adapt to various uses.
retro-tags is a tool for extracting code from fenced blocks in literate
sources and generating a tags file compatible with ctags.
AUTHORS Charles Childers crc@forthworks.com
OpenBSD 6.4 August 2019 OpenBSD 6.4
Naming Conventions
Word names in RETRO generally follow the following conventions.
General Guidelines
- Readability is important
- Be consistent
- Don't use a prefix as the first character of a name
- Don't use underscores in word names
- Use short names for indices
- Word names start with a
-for "not" - Words returning a flag end in ?
Typical Format
The word names will generally follow a form like:
[namespace:]name
The namespace: is optional, but recommended for consistency
with the rest of the system and to make it easier to identify
related words.
Case
Word names are lowercase, with a dash (-) for compound names.
hello
drop-pair
s:for-each
Variables use TitleCase, with no dash between compound names.
Base
Heap
StringBuffers
Constants are UPPERCASE, with a dash (-) for compound names.
TRUE
FALSE
f:PI
MAX-STRING-LENGTH
Namespaces
Words are grouped into broad namespaces by attaching a short prefix string to the start of a name.
The common namespaces are:
| Prefix | Contains |
| ------- | ------------------------------------------------------ |
| a: | Words operating on simple arrays |
| ASCII: | ASCII character constants for control characters |
| buffer: | Words for operating on a simple linear LIFO buffer |
| c: | Words for operating on ASCII character data |
| class: | Contains class handlers for words |
| d: | Words operating on the Dictionary |
| err: | Words for handling errors |
| io: | General I/O words |
| n: | Words operating on numeric data |
| prefix: | Contains prefix handlers |
| s: | Words operating on string data |
| v: | Words operating on variables |
| file: | File I/O words |
| f: | Floating Point words |
| unix: | Unix system call words |
Tips
Don't Start Names With Prefix Characters
Avoid using a prefix as the first character of a word name. RETRO will look for prefixes first, this will prevent direct use of the work in question.
To find a list of prefix characters, do:
'prefix: d:words-with
Don't Use Underscores
Underscores in strings are replaced by spaces. This is problematic, especially with variables. Consider:
'test_name var
#188 !test_name
In this, the string for the name is converted to "test name". The store in the second line will not add the space, so resolves to an incorrect address.
I personally recommend avoiding the use of underscores in any word names.
The Return Stack
RETRO has two stacks. The primary one is used to pass data beween words. The second one primarily holds return addresses.
Each time a word is called, the next address is pushed to the return stack.
Stack Diagrams
Most words in RETRO have a stack comment. These look like:
(-)
(nn-n)
As with all comments, a stack comment begins with ( and
should end with a ). There are two parts to the comment.
On the left side of the - is what the word consumes. On
the right is what it leaves.
RETRO uses a short notation, with one character per value taken or left. In general, the following symbols represent certain types of values.
| Notation | Represents |
| ------------------- | ----------------------- |
| b, n, m, o, x, y, z | generic numeric values |
| s | string |
| v | variable |
| p, a | pointers |
| q | quotation |
| d | dictionary header |
| f | `TRUE` or `FALSE` flag. |
In the case of something like (xyz-m), RETRO expects z to be
on the top of the stack, with y below it and x below the y
value. And after execution, a single value (m) will be left on
the stack.
Words with no stack effect have a comment of (-)
Working With Arrays
RETRO offers a number of words for operating on statically sized arrays.
Namespace
The words operating on arrays are kept in an a: namespace.
Creating Arrays
The easiest way to create an array is to wrap the values in a
{ and } pair:
{ #1 #2 #3 #4 }
{ 'this 'is 'an 'array 'of 'strings }
{ 'this 'is 'a 'mixed 'array #1 #2 #3 }
You can also make an array from a quotation which returns values and the number of values to store in the a:
[ #1 #2 #3 #3 ] a:counted-results
[ #1 #2 #3 #3 ] a:make
Accessing Elements
You can access a specific value with a:th and fetch or
store:
{ #1 #2 #3 #4 } #3 a:th fetch
Find The Length
Use a:length to find the size of the array.
{ #1 #2 #3 #4 } a:length
Duplicate
Use a:dup to make a copy of an a:
{ #1 #2 #3 #4 } a:dup
Filtering
RETRO provides a:filter which extracts matching values
from an array. This is used like:
{ #1 #2 #3 #4 #5 #6 #7 #8 } [ n:even? ] a:filter
The quote will be passed each value in the array and should return TRUE or FALSE. Values that lead to TRUE will be collected into a new array.
Mapping
a:map applies a quotation to each item in an array and
constructs a new array from the returned values.
Example:
{ #1 #2 #3 } [ #10 * ] a:map
Reduce
a:reduce takes an array, a starting value, and a quote. It
executes the quote once for each item in the array, passing the
item and the value to the quote. The quote should consume both
and return a new value.
{ #1 #2 #3 } #0 [ + ] a:reduce
Search
RETRO provides a:contains? and a:contains-string?
to search an array for a value (either a number or string) and
return either TRUE or FALSE.
#100 { #1 #2 #3 } a:contains?
'test { 'abc 'def 'test 'ghi } a:contains-string?
Implementation
In memory, an array is a count followed by the values. As an example, if you have an array:
{ #10 #20 #30 }
In memory this would be setup as:
| Offset | Value |
| ------ | ----- |
| 000 | 3 |
| 001 | 10 |
| 002 | 20 |
| 003 | 30 |
You can construct one on the fly by keeping a pointer to
here and using , to place the values. E.g.,
here [ #3 , #10 , #20 , #30 , ] dip
An example of this can be seen in this excerpt from an example (example/Primes.forth):
:create-set (-a)
here #3000 , #2 #3002 [ dup , n:inc ] times drop ;
Working With Assembly Language
RETRO runs on a virtual machine called Nga. It provides a standard assembler for this called Muri.
Muri is a simple, multipass model that's not fancy, but suffices for RETRO's needs.
Assembling A Standalone File
A small example (test.muri)
~~~
i liju....
r main
: c:put
i liiire..
i 0
: main
i lilica..
d 97
i liju....
r main
~~~
Assembling it:
retro-muri test.muri
So breaking down: Muri extracts the assembly code blocks to assemble, then proceeds to do the assembly. Each source line starts with a directive, followed by a space, and then ending with a value.
The directives are:
: value is a label
i value is an instruction bundle
d value is a numeric value
r value is a reference
s value is a string to inline
Instructions for Nga are provided as bundles. Each memory location can store up to four instructions. And each instruction gets a two character identifier.
From the list of instructions:
0 nop 5 push 10 ret 15 fetch 20 div 25 zret
1 lit 6 pop 11 eq 16 store 21 and 26 halt
2 dup 7 jump 12 neq 17 add 22 or 27 ienum
3 drop 8 call 13 lt 18 sub 23 xor 28 iquery
4 swap 9 ccall 14 gt 19 mul 24 shift 29 iinvoke
This reduces to:
0 .. 5 pu 10 re 15 fe 20 di 25 zr
1 li 6 po 11 eq 16 st 21 an 26 ha
2 du 7 ju 12 ne 17 ad 22 or 27 ie
3 dr 8 ca 13 lt 18 su 23 xo 28 iq
4 sw 9 cc 14 gt 19 mu 24 sh 29 ii
Most are just the first two letters of the instruction name. I
use .. instead of no for NOP, and the first letter of
each I/O instruction name. So a bundle may look like:
dumure..
(This would correspond to dup multiply return nop).
Runtime Assembler
RETRO also has a runtime variation of Muri that can be used when you need to generate more optimal code. So one can write:
:n:square dup * ;
Or:
:n:square \dumure.. ;
The second one will be faster, as the entire definition is one bundle, which reduces memory reads and decoding by 2/3.
Doing this is less readable, so I only recommend doing so after you have finalized working RETRO level code and determined the best places to optimize.
The runtime assembler has the following directives:
i value is an instruction bundle
d value is a numeric value
r value is a reference
Additionally, in the runtime assembler, these are reversed:
'dudumu.. i
Instead of:
i dudumu..
The runtime assembler also provides three prefixes for use in inlining machine code into a definition. These are:
\ Treat token as an assembly sequence
` Treat token as a numeric value
^ Treat token as a reference
E.g., instead of doing something like:
:n:square as{ 'dumu.... i }as ;
:test as{ 'lilica.... i #22 d 'n:square r }as ;
Just write:
:n:square \dumu.... ;
:test \lilica.. `22 ^n:square ;
Working With a Buffer
RETRO provides words for operating on a linear memory area. This can be useful in building strings or custom data structures.
Namespace
Words operating on the buffer are kept in the buffer:
namespace.
Implementation
A buffer is a linear sequence of memory. The buffer words provide a means of incrementally storing and retrieving values from it.
The buffer words keep track of the start and end of the
buffer. They also ensure that an ASCII:NULL is written
after the last value, which make using them for string
data easy.
Limitations
Only one buffer can be active at a time. RETRO provides a
buffer:preserve combinator to allow using a second one
before returning to the prior one.
Set The Active Buffer
To set a buffer as the active one use buffer:set. This takes
an address.
The buffer will be assumed to be empty. The inital value will be set to ASCII:NULL.
Add Value
Use buffer:add to append a value to the buffer. This takes
a single value and will also add an ASCII:NULL after the end
of the buffer.
Fetch Last Value
To return the last value in the buffer you can use buffer:get.
This removes the value and sets an ASCII:NULL in the memory
location the returned value occupied.
Get Data About The Buffer
RETRO provides buffer:start to get the initial address in
the buffer, buffer:end to get the last address (ignoring the
ASCII:NULL), and buffer:size to return the number of values
in the buffer.
Reset
You can reset a buffer to the empty state using buffer:empty.
Example
To begin, create a memory region to use as a buffer.
'Test d:create #1025 allot
Then you can set this as the current buffer:
&Test buffer:set
When a buffer is set, the vocabulary sets an internal index to the first address in it. This will be incremented when you add data and decremented when you remove data.
Let's add some stuff using buffer:add:
#100 buffer:add
#200 buffer:add
#300 buffer:add
And then retreive the values:
buffer:get n:put nl
buffer:get n:put nl
buffer:get n:put nl
You can remove all values using buffer:empty:
#100 buffer:add
#200 buffer:add
#300 buffer:add
buffer:empty
And ask the buffer how many items it contains:
buffer:size n:put nl
#100 buffer:add
#200 buffer:add
#300 buffer:add
buffer:size n:put nl
buffer:empty
The other functions are buffer:start, which returns
the address of the buffer, buffer:end, which returns
the address of the last value, and buffer:preserve.
The first is easy to demo:
buffer:start Test eq? n:put nl
The last one is useful. Only one buffer is ever active
at a given time. The buffer:preserve combinator lets
you execute a word, saving and restoring the current
buffer indexes. So the word could assign and use a new
buffer and this will reset the previous one after
control returns.
There are a few notes that need to be considered. The preserve combinator saves the start and current index but not the contents. If the word you call uses the same buffer, the contents will remain altered.
Finally, the buffer words have one interesting trait: they store an ASCII NULL after adding each item to the buffer. This lets one use them to build strings easily.
Test buffer:set
$h buffer:add
$e buffer:add
$l buffer:add
$l buffer:add
$o buffer:add
$, buffer:add
#32 buffer:add
$w buffer:add
$o buffer:add
$r buffer:add
$l buffer:add
$d buffer:add
buffer:start s:put nl
Working With Characters
RETRO provides words for working with ASCII characters.
Prefix
Character constants are returned using the $ prefix.
Namespace
Words operating on characters are in the c: namespace.
Classification
RETRO provides a number of words to determine if a character fits into predefined groups.
The primary words for this are:
c:consonant?c:digit?c:letter?c:lowercase?c:uppercase?c:visible?c:vowel?c:whitespace?
There are also corresponding "not" forms:
c:-consonant?c:-digit?c:-lowercase?c:-uppercase?c:-visible?c:-vowel?c:-whitespace?
All of these take a character and return either a TRUE or
FALSE flag.
Conversions
A few words are provided to convert case. Each takes a character and returns the modified character.
c:to-lowerc:to-numberc:to-upperc:toggle-case
RETRO also has c:to-string, which takes a character and
creates a new temporary string with the character.
I/O
Characters can be displayed using c:put.
$a c:put
With the default system on BSD, Linux, and macOS (and other
Unix style hosts), c:get is provided to read input. This
may be buffered, depending on the host.
Defining Words
Words are named functions. To start a word, preceed it's name with a colon. Follow this by the definition, and end with a semicolon.
E.g.,
:do-nothing ;
:square dup * ;
Working With The Dictionary
The Dictionary is a linked list containing the dictionary headers.
Namespace
Words operating on the dictionary are in the d: namespace.
Variables
Dictionary is a variable holding a pointer to the most recent
header.
Header Structure
Each entry follows the following structure:
Offset Contains
------ ---------------------------
0000 Link to Prior Header
0001 Link to XT
0002 Link to Class Handler
0003+ Word name (null terminated)
RETRO provides words for accessing the fields in a portable manner. It's recommended to use these to allow for future revision of the header structure.
Accessing Fields
Given a pointer to a header, you can use d:xt, d:class,
and d:name to access the address of each specific field.
There is no d:link, as the link will always be the first
field.
Shortcuts For The Latest Header
RETRO provides several words for operating on the most recent header.
d:last returns a pointer to the latest header. d:last<xt>
will give the contents of the d:xt field for the latest
header. There are also d:last<class> and d:last<name>.
Adding Headers
Two words exist for making new headers. The easy one is
d:create. This takes a string for the name and makes a
new header with the class set to class:data and the XT
field pointing to here.
Example:
'Base d:create
The other is d:add-header. This takes a string, a pointer
to the class handler, and a pointer for the XT field and
builds a new header using these.
Example:
'Base &class:data #10000 d:add-header
Searching
RETRO provides two words for searching the dictionary.
d:lookup takes a string and tries to find it in the
dictionary. It will return a pointer to the dictionary header
or a value of zero if the word was not found.
d:lookup-xt takes a pointer and will return the dictionary
header that has this as the d:xt field, or zero if no match
is found.
Iteration
You can use the d:for-each combinator to iterate over all
entries in the dictionary. For instance, to display the names
of all words:
[ d:name s:put sp ] d:for-each
For each entry, this combinator will push a pointer to the entry to the stack and call the quotation.
Listing Words
Most Forth systems provide WORDS for listing the names of all
words in the dictionary. RETRO does as well, but this is named
d:words.
This isn't super useful as looking through several hundred
names is annoying. RETRO also provides d:words-with to help
in filtering the results.
Example:
'class: d:words-with
Working With Floating Point
Some RETRO systems include support for floating point numbers.
When present, this is built over the system libm using the
C double type.
Floating point values are typically 64 bit IEEE 754 double precision (1 bit for the sign, 11 bits for the exponent, and the remaining 52 bits for the value), i.e. 15 decimal digits of precision.
Prefix
Floating point numbers start with a .
Examples:
Token Value .1 1.0 .0.5 0.5 .-.4 -0.4 .1.3 1.3
Namespace
Floating point words are in the f: namespace. There is also
a related e: namespace for encoded values, which allows
storing of floats in standard memory.
Operation
Floating point values exist on a separate stack, and are bigger than the standard memory cells, so can not be directly stored and fetched from memory.
The floating point system also provides an alternate stack that can be used to temporarily store values.
The following words exist for arranging values on the floating point stack. These are direct analogs to the non-prefiexd words for dealing with the data stack.
f:nipf:overf:depthf:dropf:drop-pairf:dupf:dup-pairf:dump-stackf:tuckf:swapf:rot
For the secondary floating point stack, the following words are provided:
f:pushf:popf:adepthf:dump-astack
Constants
| Name | Returns |
| -------- | ----------------- |
| `f:E` | Euler's number |
| `f:-INF` | Negative infinity |
| `f:INF` | Positive infinity |
| `f:NAN` | Not a Number |
| `f:PI` | PI |
Comparisons
The basic set of comparators are the same as those for operating on integers. These are:
f:-eq?f:between?f:eq?f:gt?f:lt?f:negative?f:positive?f:case
There are also a few additions for comparing to special values like infinity and NaN.
f:-inf?f:inf?f:nan?
Basic Math
f:*f:+f:-f:/f:absf:floorf:incf:limitf:maxf:minf:negatef:powerf:ceilingf:decf:logf:sqrtf:squaref:roundf:signf:signed-sqrtf:signed-square
Geometry
RETRO provides a small number of words for doing geometric related calculations.
| Word | Returns |
|---|---|
f:acos |
arc cosine |
f:asin |
arc sine |
f:atan |
arc tangent |
f:cos |
cosine |
f:sin |
sine |
f:tan |
tangent |
Storage and Retrieval
By leveraging the encoded value functions, RETRO is able to allow storage of floating point values in memory. This does have a tradeoff in accuracy as the memory cells are considerably smaller than a full floating point size.
You can use f:fetch to fetch a floating point value and
f:store to store one.
If you need more precision, try Kiyoshi Yoneda's FloatVar
example (example/FloatVar.forth), which includes words to
store and retrieve values using multiple cells.
f:to-numberf:to-string
I/O
The floating point vocabulary has a single I/O word, f:put,
for the display of floating point numbers.
Encoded Values
RETRO provides a means of encoding and decoding floating point values into standard integer cells. This is based on the paper "Encoding floating point values to shorter integers" by Kiyoshi Yoneda and Charles Childers.
f:E1f:to-ee:-INFe:-inf?e:INFe:MAXe:MINe:NANe:clipe:inf?e:max?e:min?e:n?e:nan?e:pute:to-fe:zero?
Working With Files
On Unix and Windows systems RETRO provides a set of words for working with files. As a pragmatic choice these are mostly modeled after the file functions in libc.
The file words are in the file: namespace.
File Access Modes
You can open a file for various operations. The functionality allowed depends on the file access mode. Valid modes in RETRO are:
file:A Open for appending; file pointer set to end of file
file:R Open for reading; file pointer set to start of file
file:R+ Open for reading and writing
file:W Open for writing
Opening A File
To open a file, pass the file name and a file mode to file:open.
'/etc/motd file:R file:open
On a successful open this will return a file handle greater than zero.
Additionally, RETRO provides a few other forms for opening files.
To open a file for reading:
'/etc/motd file:open<for-reading>
This will return the size of the file (as NOS) and the file handle (as TOS).
To open a file for writing:
'/tmp/test file:open<for-writing>
This returns the file handle.
To open a file for append operations:
'/tmp/test file:open<for-append>
As with file:open<for-reading>, this returns both the size of
the file and the file handle.
Closing A File
To close a file, pass the file handle to file:close.
'/etc/motd file:A file:open file:close
Reading From A File
To read a byte from an open file, pass the file handle to the
file:read word.
@FID file:read n:put
To read a line from a file, pass the file handle to the word
file:read-line.
@FID file:read-line s:put
The line is read into a temporary string buffer. Move the text to a safe place if you aren't using it quickly or if the length of the line is bigger than the size of a temporary string.
Writing To A File
To write a byte to a file, pass it and the file handle to
file:write.
$h @FID file:write
$e @FID file:write
$l @FID file:write
$l @FID file:write
$o @FID file:write
Though cells are 32 or 64 bits in size, only the byte value will be written to the file.
Deleting Files
You can delete a file by passing the file name to file:delete.
/tmp/test file:delete
Check For File Existance
Use file:exists? to detect the existance of a file. Pass it a
file name and it will return TRUE if existing or FALSE if
it does not.
'/etc/motd file:exists?
This will also return TRUE if the filename is a directory.
Flush Caches
Use file:flush to flush the system caches for a file. Pass a
file handle to this.
@FID file:flush
Seek A Position Within A File
You can use file:seek to move the internal file pointer
for a given file. Pass this the new location and a file.
#100 @FID file:seek
The location for the file pointer is a fixed offset from the start of the file, not a relative offset.
Get The Current Position Within A File
To find the current value of the file pointer within a file
just pass the file handle to file:tell.
@FID file:tell
This returns a number that is the number of bytes into the file that the file pointer is currently at.
Determine The Size Of A File
Use file:size to return the size of a file. Pass this a file
handle and it will return the size of a file, or 0 if empty. If
the file is a directory, it returns -1.
@FID file:size
Reading An Entire File
If you want to read an entire file into memory you can use
file:slurp. This takes the starting address of a memory
region and the name of the file.
here '/etc/motd file:slurp
Take care that the memory buffer is large enough for the file being read or you will run into problems.
Writing A String To A File
If you have a string that you want to write to a file, replacing
any existing contents, you can use file:spew. This takes the
string to write and a file name.
'hello_world '/tmp/test.txt file:spew
Iterating Over A File, Line By Line
You can easily iterate over each line in a file using the word
file:for-each-line. This will take a file name and a quote,
read each line into a temporary string, then pass this string to
the quote.
'/etc/motd [ s:put nl ] file:for-each-line
Loops
RETRO provides several words for creating loops.
Unconditional Loops
An unconditional loop begins with repeat and ends with again.
:test repeat #1 n:put sp again ;
test
Unconditional loops must be inside a definition or quote. To exit
one of these, use 0;, -if; or if;.
:test #100 repeat 0; dup n:put sp n:dec again ;
test
:test #100 repeat dup #50 eq? [ 'done! s:put nl ] if; n:dec again ;
test
You can also achieve this via recursion:
:test 0; dup n:put sp n:dec test ;
#100 test
Be careful with recursion as the virtual machine will have a limited amount of space for the address stack and recursing too many times can cause a stack overflow.
Conditional Loops
There are two conditional looping combinators: while and until.
Both take a quote and execute it, checking a returned flag to decide
when to stop running.
#0 [ dup n:put sp n:inc dup #10 eq? ] until
#10 [ dup n:put sp n:dec dup n:-zero? ] while
Counted Loops
There are two combinators for counted loops. These are times and
times<with-index>.
#0 #10 [ dup n:put sp n:inc ] times nl
#10 [ I n:put sp ] times<with-index>
The times<with-index> provides an index via the I, J, and
K words. I will be the index of the current loop, with J and
K being the indexes of the next two older loops.
The loop indexes can be accessed outside the loop body:
:display I n:square n:put sp ;
:squares [ display ] times<with-index> nl ;
#100 squares
Tradeoffs
The unconditional loop form is more efficient as it's just a
simple jump operation. The times counted loops are a little
slower, but can be cleaner and more readable in many cases. The
times<with-index> form is significantly slower than the other
two forms.
Working With Numbers
Numbers in RETRO are signed integers.
Token Prefix
All numbers start with a # prefix.
Namespace
Most words operating on numbers are in the n: namespace.
Range of Values
A default RETRO system with 32 bit cells provides a range of -2,147,483,648 to 2,147,483,647. For 64 bit systems, the range will be -9,223,372,036,854,775,807 to 9,223,372,036,854,775,806.
You can check the range your VM and image support using:
n:MIN
n:MAX
These will return the limits for your system.
Comparisons
RETRO provides a number of comparison words for numeric values.
The basic comparators are:
-eq?
eq?
lt?
lteq?
gt?
gteq?
Additionally RETRO also provides:
n:-zero?
n:between?
n:even?
n:negative?
n:odd?
n:positive?
n:strictly-positive?
n:zero?
Basic Operations
+
-
*
/
mod
/mod
n:abs
n:dec
n:inc
n:limit
n:max
n:min
n:negate
n:pow
n:sqrt
n:square
Conversions
You can convert a number to a string with n:to-string or
to a floating point value with n:to-float.
#123 n:to-float f:put
#123 n:to-string s:put
Display
To display a number, use n:put.
#123 n:put
Working With Pointers
Prefix
Pointers are returned by the & prefix.
Examples
'Base var
&Base fetch
#10 &Base store
#10 &n:inc call
Notes
The use of & to get a pointer to a data structure (with a
word class of class:data) is not required. I like to use it
anyway as it makes my intent a little clearer.
Pointers are useful with combinators. Consider:
:abs dup n:negative? [ n:negate ] if ;
Since the target quote body is a single word, it is more efficient to use a pointer instead:
:abs dup n:negative? &n:negate if ;
The advantages are speed (saves a level of call/return by avoiding the quotation) and size (for the same reason). This may be less readable though, so consider the balance of performance to readability when using this approach.
Quotations
Quotes are anonymous functions. RETRO uses these as the basis for executable flow control and combinatorial logic.
Using Quotations
To make a quotation, surround the code with square brackets. E.g.,
#1 #2 eq? [ 'No_match s:put nl ] -if
Quotes can be nested:
[ #3 [ #4 ] dip ] call
After creation, a pointer to the quotation is left on the stack (or is compiled into the current definition).
Combinators
Words operating on quotations are called combinators; these are discussed in Using Combinators.
Implementation
A quotation is compiled as:
... code before quotation ...
i liju.... (if_compiling_only)
d address after quotation (if_compiling_only)
... code for quotation
i re...... (this_is_where_the_quote_ends)
i li......
d address of code for quotation
... code after quotation ....
Other Notes
Quotations are used heavily in RETRO. They give the source a feel that's different from traditional Forth, and allow for a more consistent syntax.
For instance, in a traditional Forth, you might have some conditionals:
IF ... THEN
IF ... ELSE ... THEN
IF ... EXIT THEN
RETRO uses conditional combinators for these:
[ ... ] if
[ ... ] [ ... ] choose
[ ... ] if;
Or loops:
FOR ... NEXT
Is replaced by:
[ ... ] times
This can also extend to stack flow. Sequences like:
>R ... >R
DUP >R ... >R
Become:
[ ... ] dip
[ ... ] sip
And forms like:
1 2 3 * swap 3 * swap
Can be replaced with a combinator like:
#1 #2 [ #3 * ] bi@
While there is a different set of words to learn, I find that overall there's less noise from low level stack shuffling words and the added consistency with regards to overall syntax has been nice as I was never fond of the multiple forms that existed in traditional Forth.
Sockets
On Unix hosts, RETRO provides an optional set of words for using network sockets.
Create a Socket
To create a new socket, just run:
socket:create
This will return a socket handle.
Bind To A Port
To bind to a port, pass the port number and socket handle
to socket:bind. The port should be a string. This will return
0 if successful, -1 if not successful, and an error code.
'9998 @Sock socket:bind
Configure To Allow Incoming Connections
To prepare a socket for incoming connections use socket:listen. This will take a backlog count and a socket handle. It returns a flag (0 success, -1 failed) and an error code.
#3 @Sock socket:listen
Accept Connections
To accept connections pass the socket handle to socket:accept.
This returns a new socket for the connection and an error code.
@Sock socket:accept
Make A Connection
To connect to a server using the socket:
'forth.works '70 socket:configure
@Sock socket:connect
socket:connect will return a status code and an error code.
Writing To A Socket
To write a string to a socket, use socket:send. This will
take a string and a socket handle and will return the number
of bytes sent and an error code.
'test @Sock socket:send
Reading From A Socket
To read data from a socket pass an address, a maximum number of
bytes, and the socket handle to socket:recv. This will return
the number of bytes received and an error code. The bytes will
be stored in memory starting at the specified address.
here #1024 @Sock socket:recv
Close a Socket
To close a socket, pass the socket handle to socket:close.
@Socket socket:close
Unix Scripting
RETRO on Unix hosts is designed to play well with scripting.
Shebang
To run an entire program directly, start the file with the standard shebang and make the file executable:
#!/usr/bin/env retro
This requires the retro binary to be in your path.
Arguments
RETRO provides several words in the script: namespace for accessing
command line arguments.
The number of arguments can be accessed via script:arguments. This
will return a number with the arguments, other than the script
name.
script:arguments '%n_arguments_passed\n s:format s:put
To retreive an argument, pass the argument number to script:get-argument:
script:arguments [ I script:get-argument s:put nl ] indexed-times
And to get the name of the script, use script:name.
script:name s:put
Mixing
With use of the Unu literate format, it's possible to mix both shell and RETRO code into a single script. As an example, this is a bit of shell that runs itself via retro for each .retro file in the current directory tree:
#!/bin/sh
# shell part
find . -name '*.retro' -print0 | xargs -0 -n 1 retro $0
exit
# retro part
This will scan a source file and do something with it:
~~~
... do stuff ...
~~~
Working With Strings
Strings in RETRO are NULL terminated sequences of values representing characters. Being NULL terminated, they can't contain a NULL (ASCII 0).
The character words in RETRO are built around ASCII, but
strings can contain UTF8 encoded data if the host platform
allows. Words like s:length will return the number of bytes,
not the number of logical characters in this case.
Prefix
Strings begin with a single '.
'Hello
'This_is_a_string
'This_is_a_much_longer_string_12345_67890_!!!
RETRO will replace spaces with underscores. If you need both
spaces and underscores in a string, escape the underscores and
use s:format:
'This_has_spaces_and_under\_scored_words. s:format
Namespace
Words operating on strings are in the s: namespace.
Lifetime
At the interpreter, strings get allocated in a rotating buffer.
This is used by the words operating on strings, so if you need
to keep them around, use s:keep or s:copy to move them to
more permanent storage.
In a definition, the string is compiled inline and so is in permanent memory.
You can manually manage the string lifetime by using s:keep
to place it into permanent memory or s:temp to copy it to
the rotating buffer.
Mutability
Strings are mutable. If you need to ensure that a string is not altered, make a copy before operating on it or see the individual glossary entries for notes on words that may do this automatically.
Searching
RETRO provides four words for searching within a string.
s:contains-char?s:contains-string?s:index-ofs:index-of-string
Comparisons
s:eq?s:case
Extraction
To obtain a new string containing the first n characters from
a source string, use s:left:
'Hello_World #5 s:left
To obtain a new string containing the last n characters from
a source string, use s:right:
'Hello_World #5 s:right
If you need to extract data from the middle of the string, use
s:substr. This takes a string, the offset of the first
character, and the number of characters to extract.
'Hello_World #3 #5 s:substr
Joining
You can use s:append or s:prepend to merge two strings.
'First 'Second s:append
'Second 'First s:prepend
Tokenization
s:tokenizes:tokenize-on-strings:splits:split-on-string
Conversions
To convert the case of a string, RETRO provides s:to-lower
and s:to-upper.
s:to-number is provided to convert a string to an integer
value. This has a few limitations:
- only supports decimal
- non-numeric characters will result in incorrect values
Cleanup
RETRO provides a handful of words for cleaning up strings.
s:chop will remove the last character from a string. This
is done by replacing it with an ASCII:NULL.
s:trim removes leading and trailing whitespace from a string.
For more control, there is also s:trim-left and s:trim-right
which let you trim just the leading or trailing end as desired.
Combinators
s:for-eachs:filters:map
Other
s:evaluates:copys:reverses:hashs:lengths:replaces:formats:empty
Controlling The Temporary Buffers
As dicussed in the Lifetime subsection, temporary strings are allocated in a rotating buffer. The details of this can be altered by updating two variables.
| Variable | Holds |
| ------------- | ---------------------------------------- |
| TempStrings | The number of temporary strings |
| TempStringMax | The maximum length of a temporary string |
For example, to increase the number of temporary strings to 48:
#48 !TempStrings
The defaults are:
| Variable | Default |
| ------------- | ------- |
| TempStrings | 32 |
| TempStringMax | 512 |
It's also important to note that altering these will affect the memory map for all temporary buffers. Do not use anything already in the buffers after updating these or you will risk data corruption and possible crashes.
Using Combinators
A combinator is a function that consumes functions as input. They are used heavily by the RETRO system.
Types of Combinators
Combinators are divided into three primary types: compositional, execution flow, and data flow.
Compositional
A compositional combinator takes elements from the stack and returns a new quote.
curry takes a value and a quote and returns a new quote
applying the specified quote to the specified value. As an
example,
:acc (n-) here swap , [ dup v:inc fetch ] curry ;
This would create an accumulator function, which takes an initial value and returns a quote that will increase the accumulator by 1 each time it is invoked. It will also return the latest value. So:
#10 acc
dup call n:put
dup call n:put
dup call n:put
Execution Flow
Combinators of this type execute other functions.
Fundamental
call takes a quote and executes it immediately.
[ #1 n:put ] call
&words call
Conditionals
RETRO provides three primary combinators for use with
conditional execution of quotes. These are choose, if,
and -if.
choose takes a flag and two quotes from the stack. If the
flag is true, the first quote is executed. If false, the
second quote is executed.
#-1 [ 'true s:put ] [ 'false s:put ] choose
#0 [ 'true s:put ] [ 'false s:put ] choose
if takes a flag and one quote from the stack. If the flag is
true, the quote is executed. If false, the quote is discarded.
#-1 [ 'true s:put ] if
#0 [ 'true s:put ] if
-if takes a flag and one quote from the stack. If the flag is
false, the quote is executed. If true, the quote is discarded.
#-1 [ 'false s:put ] -if
#0 [ 'false s:put ] -if
RETRO also provides case and s:case for use when you have
multiple values to check against. This is similar to a switch
in C.
case takes two numbers and a quote. The initial value is
compared to the second one. If they match, the quote is
executed. If false, the quote is discarded and the initial
value is left on the stack.
Additionally, if the first value was matched, case will exit
the calling function, but if false, it returns to the calling
function.
s:case works the same way, but for strings instead of simple
values.
:test (n-)
#1 [ 'Yes s:put ] case
#2 [ 'No s:put ] case
drop 'No idea s:put ;
Looping
Several combinators are available for handling various looping constructs.
while takes a quote from the stack and executes it repeatedly
as long as the quote returns a true flag on the stack. This flag
must be well formed and equal -1 or 0.
#10 [ dup n:put sp n:dec dup 0 -eq? ] while
times takes a count and quote from the stack. The quote will
be executed the number of times specified. No indexes are pushed
to the stack.
#1 #10 [ dup n:put sp n:inc ] times drop
There is also a times<with-index> variation that provides
access to the loop index (via I) and parent loop indexes
(via J and K).
#10 [ I n:put sp ] times<with-index>
Data Flow
These combinators exist to simplify stack usage in various circumstances.
Preserving
Preserving combinators execute code while preserving portions of the data stack.
dip takes a value and a quote, moves the value off the main
stack temporarily, executes the quote, and then restores the
value.
#10 #20 [ n:inc ] dip
Would yield the following on the stack:
11 20
sip is similar to dip, but leaves a copy of the original
value on the stack during execution of the quote. So:
#10 [ n:inc ] sip
Leaves us with:
11 10
Cleave
Cleave combinators apply multiple quotations to a single value or set of values.
bi takes a value and two quotes, it then applies each quote to
a copy of the value.
#100 [ n:inc ] [ n:dec ] bi
tri takes a value and three quotes. It then applies each quote
to a copy of the value.
#100 [ n:inc ] [ n:dec ] [ dup * ] tri
Spread
Spread combinators apply multiple quotations to multiple values. The asterisk suffixed to these function names signifies that they are spread combinators.
bi* takes two values and two quotes. It applies the first
quote to the first value and the second quote to the second
value.
#1 #2 [ n:inc ] [ #2 * ] bi*
tri* takes three values and three quotes, applying the
first quote to the first value, the second quote to the
second value, and the third quote to the third value.
#1 #2 #3 [ n:inc ] [ #2 * ] [ n:dec ] tri*
Apply
Apply combinators apply a single quotation to multiple values. The @ sign suffixed to these function names signifies that they are apply combinators.
bi@ takes two values and a quote. It then applies the quote to
each value.
#1 #2 [ n:inc ] bi@
tri@ takes three values and a quote. It then applies the quote
to each value.
#1 #2 #3 [ n:inc ] tri@
RETRO also provides for-each combinators for various data
structures. The exact usage of these varies; consult the
Glossary and relevant chapters for more details on these.
Word Classes
Word classes are one of the two elements at the heart of RETRO's interpreter.
There are different types of words in a Forth system. At a minimum there are data words, regular words, and immediate words. There are numerous approaches to dealing with this.
In RETRO I define special words which receive a pointer and
decide how to deal with it. These are grouped into a class:
namespace.
How It Works
When a word is found in the dictionary, RETRO will push a
pointer to the definition (the d:xt field) to the stack
and then call the word specified by the d:class field.
The word called is responsible for processing the pointer passed to it.
As a simple case, let's look at immediate words. These are
words which will always be called when encountered. A common
strategy is to have an immediacy bit which the interpreter
will look at, but RETRO uses a class for this. The class is
defined:
:class:immediate (a-) call ;
Or a normal word. These should be called at interpret time or compiled into definitions. The handler for this can look like:
:class:word (a-) compiling? [ compile:call ] [ call ] choose ;
Using Classes
The ability to add new classes is useful. If I wanted to add a category of word that preserves an input value, I could do it with a class:
:class:duplicating (a-)
compiling? [ &dup compile:call ] [ &dup dip ] choose
class:word ;
:duplicating &class:duplicating reclass ;
:. n:put nl ; duplicating
#100 . . .
Checking The Version
RETRO releases add and change things. You can use the Version
variable to determine the version in use and react accordingly.
@Version #201906 eq? [ 'Needs_2019.6! s:put nl bye ] if
This can be also be used to conditionally load compatibility files:
(If_newer_than_2016.6,_load_aliases_for_renamed_words)
@Version #201906 gt? [ 'Renamed_2019.6.forth include ] if
Version Number Format
The version is a six digit number encoding the year and month of the release. So:
201901 is 2019.1
201906 is 2019.6
201911 is 2019.11
A #100 /mod will suffice to split these if needed.
Errors
RETRO does only minimal error checking.
Non-Fatal
A non-fatal error will be reported on word not found during interactive or compile time. Note that this only applies to calls: if you try to get a pointer to an undefined word, the returned pointer will be zero.
Fatal
A number of conditions are known to cause fatal errors. The main ones are stack overflow, stack underflow, and division by zero.
On these, RETRO will generally exit. For stack depth issues, the VM will attempt to display an error prior to exiting.
In some cases, the VM may get stuck in an endless loop. If this occurs, try using CTRL+C to kill the process, or kill it using whatever means your host system provides.
Rationale
Error checks are useful, but slow - especially on a minimal system like RETRO. The overhead of doing depth or other checks adds up quickly.
As an example, adding a depth check to drop increases the
time to use it 250,000 times in a loop from 0.16 seconds to
1.69 seconds.
Lexical Scope
RETRO has a single dictionary, but does provide a means of using lexical scope to keep this dictionary clean.
Example
{{
'A var
:++A &A v:inc ;
---reveal---
:B ++A ++A @A n:put nl ;
}}
In this example, the lexical namespace is created with {{. A
variable (A) and word (++A) are defined. Then a marker is
set with ---reveal---. Another word (B) is defined, and the
lexical area is closed with }}.
The headers between {{ and ---reveal--- are then hidden from
the dictionary, leaving only the headers between ---reveal---
and }} exposed.
Notes
This only affects word visibility within the scoped area. As an example:
:a #1 ;
{{
:a #2 ;
---reveal---
:b 'a s:evaluate n:put ;
}}
In this, after }} closes the area, the :a #2 ; is hidden and
the s:evaluate will find the :a #1 ; when b is run.
The Stacks
The stacks are a defining feature of Forth. They are are used to pass data between words and to track return addresses for function calls.
RETRO always has two stacks, and optionally (if built with floating point support) a third.
Data Stack
This is the primary stack. Values are placed here, passed to words which consume them and then return results. When I refer to "the stack", this is the one I mean. Learning to use the stack is a crucial part to making effective use of RETRO.
Placing Values On The Stack
Values can be placed on the stack directly.
| Example | Action |
| -------------- | ---------------------------------------- |
| `#300123` | Push the number `300123` to the stack |
| `$h` | Push the ASCII code for `h` to the stack |
| `'hello_world` | Push a pointer to a string to the stack |
| `&fetch` | Push the address of `fetch` to the stack |
Reordering The Stack
RETRO provides a number of shufflers for reordering items on the stack.
Some of the most common ones are:
| Word | Before | After |
| ------- |--------- | -------- |
| dup | #1 | #1 #1 |
| drop | #1 #2 | #1 |
| swap | #1 #2 | #2 #1 |
| over | #1 #2 | #1 #2 #1 |
| tuck | #1 #2 | #2 #1 #2 |
| nip | #1 #2 | #2 |
| rot | #1 #2 #3 | #3 #1 #2 |
You can use push and pop to move values to and from the
address stack. Make sure you pop them back before the word
ends or RETRO will crash. These two words can not be used
at the interpreter.
There is also a special one, reorder, which allows for big
stack restructuring. This is slow but can be very useful.
As an example, let's say we have four values:
#1 #2 #3 #4
And we want them to become:
#4 #3 #2 #1
Doing this with the basic shufflers is difficult. You could end up with something similar to:
swap rot push rot pop swap
But with reorder, you can just express the before and after
states:
'abcd 'dcba reorder
Resetting The Stack
If you need to quickly empty the stack, use reset.
Get The Stack Depth
To find out how many items are on the stack, use depth.
Displaying The Stack
You can display the stack by running dump-stack.
Data Flow Combinators
RETRO provides combinators for working with data order on the stack. These are covered in a later chapter and are worth learning to use as they can help provide a cleaner, more structured means of working.
Tips
The stack is not an array in addressable memory. Don't try to treat it like one.
Address Stack
This stack primarily holds return addresses for function calls.
You normally won't need to directly interact with this stack,
but you can use push and pop to move values between the
data stack and this.
Floating Point Stack
If you are using a build with floating point support a third stack will be present. Floating point values are kept and passed between words using this.
See the Floating Point chapter for more details on this.
Tips
I recommend keeping the data stack shallow. Don't try to juggle too much; it's better to factor definitions into shorter ones that deal with simpler parts of the stack values than to have a big definition with a lot of complex shuffling.
Notes
The standard system is configured with a very deep data stack (around 2,000 items) and an address stack that is 3x deeper. In actual use, your programs are unlikely to ever need this, but if you do, keep the limits in mind.
Internals: Nga Virtual Machine
Overview
At the heart of RETRO is a simple MISC (minimal instruction set computer) processor for a dual stack architecture.
This is a very simple and straightforward system. There are 30 instructions. The memory is a linear array of signed 32 bit values. And there are two stacks: one for data and one for return addresses.
Instruction Table
| Opcode | Muri | Full Name | Data Stack | Address Stack |
|---|---|---|---|---|
| 0 | .. | nop | - | - |
| 1 | li | lit | -n | - |
| 2 | du | dup | n-nn | - |
| 3 | dr | drop | n- | - |
| 4 | sw | swap | xy-yx | - |
| 5 | pu | push | n- | -n |
| 6 | po | pop | -n | n- |
| 7 | ju | jump | a- | - |
| 8 | ca | call | a- | -A |
| 9 | cc | conditional call | af- | -A |
| 10 | re | return | - | A- |
| 11 | eq | equality | xy-f | - |
| 12 | ne | inequality | xy-f | - |
| 13 | lt | less than | xy-f | - |
| 14 | gt | greater than | xy-f | - |
| 15 | fe | fetch | a-n | - |
| 16 | st | store | na- | - |
| 17 | ad | addition | xy-n | - |
| 18 | su | subtraction | xy-n | - |
| 19 | mu | multiplication | xy-n | - |
| 20 | di | divide & remainder | xy-rq | - |
| 21 | an | bitwise and | xy-n | - |
| 22 | or | bitwise or | xy-n | - |
| 23 | xo | bitwise xor | xy-n | - |
| 24 | sh | shift | xy-n | - |
| 25 | zr | zero return | n-? | - |
| 26 | ha | halt | - | - |
| 27 | ie | i/o enumerate | -n | - |
| 28 | iq | i/o query | n-xy | - |
| 29 | ii | i/o invoke | ...n- | - |
Encoding
Up to four instructions can be packed into each memory cell.
As an example,
Opcode 4 Opcode 3 Opcode 2 Opcode 1
00000000:00000000:00000000:00000000
If we have a bundle of duliswst, it would look like:
st sw li du
00010000:00000100:00000001:00000010
Each li should have a value in the following cell(s). These
values will be pushed to the stack. E.g., lili.... and
1, 2:
00000000:00000000:00000001:00000001
00000000 00000000 00000000 00000001 (1)
00000000 00000000 00000000 00000010 (2)
Shifts
sh performs a bitwise arithmetic shift operation.
This takes two values:
xy
And returns a single one:
z
If y is positive, this shifts x right by y bits. If negative,
it shifts left.
Queries: Memory, Stacks
The fe instruction allows queries of some data related to
the Nga VM state. These are returned by reading from negative
addresses:
| Address | Returns |
|---|---|
| -1 | Data stack depth |
| -2 | Address stack depth |
| -3 | Maximum Image Size |
| -4 | Minimum Integer Value |
| -5 | Maximum Integer Value |
I/O Devices
Nga provides three instructions for interacting with I/O devices. These are:
ie i/o enumerate returns the number of attached devices
iq i/o query returns information about a device
ii i/o interact invokes an interaction with a device
As an example, with an implementation providing an output source, a block storage system, and keyboard:
ie will return `3` since there are three i/o devices
0 iq will return 0 0, since the first device is a screen (0)
with a version of 0
1 iq will return 1 3, since the second device is a block
storage (3), with a version of 1
2 iq will return 0 1, since the third device is a keyboard
(1), with a version of 0
In this case, some interactions can be defined:
: c:put
i liiire..
d 0
: c:get
i liiire..
d 2
Setup the stack, push the device ID to the stack, and then use
ii to invoke the interaction.
A RETRO system requires one I/O device (a generic output for a single character). This must be the first device, and must have a device ID of 0.
All other devices are optional and can be specified in any order.
The currently supported and reserved device identifiers are:
| ID | Device Type | Notes |
|---|---|---|
| 0000 | Generic Output | Always present as device 0 |
| 0001 | Keyboard | |
| 0002 | Floating Point | |
| 0003 | Block Storage | Raw, 1024 cell blocks |
| 0004 | Filesystem | Unix-style Files |
| 0005 | Network: Gopher | Make gopher requests |
| 0006 | Network: HTTP | Make HTTP requests |
| 0007 | Network: Sockets | |
| 0008 | Syscalls: Unix | |
| 0009 | Scripting Hooks | |
| 0010 | Random Number |
This list may be revised in the future. The only guaranteed stable indentifier is 0000 for generic output.
Internals: Interface Layers
Nga provides a virtual processor and an extensible way of adding I/O devices, but does not provide any I/O itself. Adding I/O is the responsability of the interface layer.
An interface layer will wrap Nga, providing at least one I/O device (a generic output target), and a means of interacting with the retro image.
It's expected that this layer will be host specific, adding any system interactions that are needed via the I/O instructions. The image will typically be extended with words to use these.
Internals: I/O
RETRO provides three words for interacting with I/O. These are:
io:enumerate returns the number of attached devices
io:query returns information about a device
io:invoke invokes an interaction with a device
As an example, with an implementation providing an output source, a block storage system, and keyboard:
io:enumerate will return `3` since there are three
i/o devices
#0 io:query will return 0 0, since the first device
is a screen (type 0) with a version of 0
#1 io:query will return 1 3, since the second device is
block storage (type 3), with a version of 1
#2 io:query will return 0 1, since the last device is a
keyboard (type 1), with a version of 0
In this case, some interactions can be defined:
:c:put #0 io:invoke ;
:c:get #2 io:invoke ;
Setup the stack, push the device ID, and then use io:invoke
to invoke the interaction.
A RETRO system requires one I/O device (a generic output for a single character). This must be the first device, and must have a device ID of 0.
All other devices are optional and can be specified in any order.
Internals: The Retro Image
The actual RETRO language is stored as a memory image for Nga.
Format
The image file is a flat, linear sequence of signed 32-bit values. Each value is stored in little endian format. The size is not fixed. An interface should check when loading to ensure that the physical image is not larger than the emulated memory.
Header
The image will start with two cells. The first is a liju.... instruction, the second is the target address for the jump. This serves to skip over the rest of the data and reach the actual entry point.
This is followed by a pointer to the most recent dictionary header, a pointer to the next free address in memory, and then the RETRO version number.
| Offset | Contains |
| ------ | --------------------------- |
| 0 | lit call nop nop |
| 1 | Pointer to main entry point |
| 2 | Dictionary |
| 3 | Heap |
| 4 | RETRO version |
The actual code starts after this header.
The version number is the year and month. As an example,
the 12.2019.6 release will have a version number of
201906.
Layout
Assuming an Nga built with 524287 cells of memory:
| RANGE | CONTAINS |
| --------------- | ---------------------------- |
| 0 - 1024 | rx kernel |
| 1025 - 1535 | token input buffer |
| 1536 + | start of heap space |
| ............... | free memory for your use |
| 506879 | buffer for string evaluate |
| 507904 | temporary strings (32 * 512) |
| 524287 | end of memory |
The buffers at the end of memory will resize when specific variables related to them are altered.
Using The Glossary
The Glossary is a valuable resource. It provides information on the RETRO words.
Example Entry
f:+
Data: -
Addr: -
Float: FF-F
Add two floating point numbers, returning the result.
Class: class:word | Namespace: f | Interface Layer: rre
Example #1:
.3.1 .22 f:+
Reading The Entry
An entry starts with the word name.
This is followed by the stack effect for each stack. All RETRO systems have Data and Address stacks, some also include a floating point stack).
The stack effect diagrams are followed by a short description of the word.
After the description is a line providing some useful data. This includes the class handler, namespace prefix, and the interface layer that provides the word.
Words in all systems will be listed as all. Some words (like
the pb: words) are only on specific systems like iOS. These
can be identified by looking at the interface layer field.
At the end of the entry may be an example or two.
Access Online
The latest Glossary can be browsed at http://forthworks.com:9999 or gopher://forthworks.com:9999
Historical Papers and Notes
On the Naming of RETRO
Taken from http://lists.tunes.org/archives/tunes-lll/1999-July/000121.html
On Fri, Jul 30, 1999 at 07:43:54PM -0400, Paul Dufresne wrote:
My brother did found it funny that Retro is called like that. For him retro means going back (generally in time) so this does not looks like a name of a OS to come. So he'd like to know from where the name came.
Heheh, here's the story: When I started playing with OS stuff last year (not seriously), I was reading about some old things like FORTH and ITS, dating back to the 1960's and 70's. The past few years in America, there's been a revival of disco music (along with bell bottoms, platform shoes, and all that crap) and they call it "retro". Now, my OS was named by musicians.. I was telling a fellow musician about my ideas, how it would be cool to have a small OS that isn't bloated and unmanageable like Windows... go back to the 70's and resurrect a line of software that died out. He goes "hmm.. sounds kinda retro.."
I think it sounds kinda rebellious, which is a Good Thing now that everybody hates the M$ empire. :) It seems like other people are as sick of the future as I am. Look at TUNES, the idea there isn't to make some great new invention, just take some decades-old ideas and combine them in one OS. The first time I saw Knuth's "Art of Computer Programming" in the library I thought "god that looks old.. 1973!!! nevermind.." Now it's my programming bible. Find me something better published in the 90's.. if such a thing exists, it'll be like a needle in a haystack. "Newer" doesn't necessarily mean "better".
New cars = flimsier
New farming methods = more devastating
New version of Netscape = more bloat, more bullshit
One thing is better now: computer hardware. Give me 70's software on 90's and 00's hardware :)
- Tom Novelli tcn@tunes.org
The Design Philosophy of RETRO Native Forth
Computer software is a technology in its infancy, a mere fifty years old. The last 25 years in particular have seen an explosion in the software business. However, software has seen little innovation while hardware technology has improved phenomenally (notwithstanding the advent of lousy slave-made parts). Proven software techniques of forty years ago have yet to reach widespread use, in deference to the "latest and greatest" proprietary solutions of dubious value. Thanks to agressive marketing, we make huge investments in these dead-end technologies (through our businesses and governments, if not personally) and we end up with a reliance on a heap of complicated, error-prone, poorly understood junk software.
Complexity will dominate the software industry for the foreseeable future. The Retro philosophy is a simple alternative for those willing to make a clean break with legacy software. A Retro system can communicate with other systems, but it won't run much legacy software, especially proprietary software without source code. An emulation layer could be added, but doing so would defeat the purpose of a simple operating system. I think TCP/IP support is all the compatibility that's needed.
At first Retro will appeal to computer hobbyists and electronic engineers. Once the rough edges are smoothed out, it could catch on with ordinary folks who don't like waiting five minutes just to check their email (not to mention the long hours of setup and maintenance). Game programmers who take their craft seriously may also be interested. Businesses might even see a use for it, if the managers decide it's more cost-effective to carefully design software for specific needs, rather than buying off-the-shelf crap and spending countless manhours working around the bugs. Since it's not practical for businesses to make a clean break, my advice is to run Retro (and its ilk) on separate machines connected by a network. Retro is efficient enough to run on older machines that would otherwise sit idle, being too slow for the latest Microsoft bloatware (or Linux, for that matter).
I strive to avoid the extraneous. That applies even to proven technologies, if I don't need them. If my computer isn't set up for people to log in over the network, I don't want security features; they just get in the way. If I'm only running programs I wrote, I should be able to run them with full access to the hardware; I don't need protection from viruses. If I download something I don't trust, then I can run it in an isolated process, which is customary with Unix and kin. But that's not core functionality. All that's needed is the flexibility to add things like security, graphical interfaces, and distributed processing - if the need ever arises.
In programming languagues, I was misled. It's the Tower of Babel all over again. The thousands of languages in existence all fall into a handful of archetypes: Assembler, LISP, FORTRAN and FORTH represent the earliest descendants of nearly all languages. I hesitate to name a definitive "object-oriented" language, and here's why: Object-Oriented programming is just a technique, and any language will suffice, even Assembler. The complexites of fancy languages like Ada and C++ are a departure from reality -- the reality of the actual physical machine. When it all boils down, even LISP, FORTRAN and FORTH are only extensions of the machine.
I chose FORTH as the "native tongue" of Retro. LISP, FORTRAN, and other languages can be efficiently implemented as extensions of FORTH, but the reverse isn't so efficient. Theoretically all languages are equivalent, but when design time, compilation time, and complexity are accounted for, FORTH is most efficient. FORTH also translates most directly to the hardware. (In fact, FORTH has been implemented in hardware; these "stack machines" are extremely efficient.) FORTH is also the easiest language to implement from scratch - a major concern when you're trying to make a clean break. So with simplicity in mind, FORTH was the obvious choice.
I'm perfectly happy working with text only, and I go to great lengths to avoid using the standard graphical environments, which have major problems: windows, pulldown menus, and mice. Windows can't share the screen nicely; that idea is hopeless. Pulldowns are tedious. Mice get in the way of typing without reducing the need for it; all they give me is tendonitis. Their main use is for drawing.
Some of my favorite interfaces: Telix, Telegard BBS, Pine, Pico, Lynx, and ScreamTracker. All "hotkey" interfaces where you press a key or two to perform an action. Usually the important commands are listed at the bottom of the screen, or at least on a help screen. The same principles apply to graphical interfaces: use the full screen, except for a status and menu area on one edge. Resist the temptation to clutter up the screen.
As for switching between programs, the Windows methods suck; the only thing worse is Unix job control (jobs, fg, and such). The Linux method is tolerable: Alt-Arrows, Alt-F1, Alt-F2, etc. Still, things could be better: F11 and F12 cycle back and forth through all open programs; Alt-F1 assigns the currently selected program to F1, and likewise for the other function keys. Programs just won't use function keys - Control and Alt combinations are less awkward and easier to remember, besides. I'll also want a "last channel" key and a "task list" key; maybe I'll borrow those stupid Win95 keys. The Pause key will do like it says - pause the current program - and Ctrl-Pause (Break) will kill it.
One more thing: consistency. I like programs to look different so I can tell them apart, but the keys should be the same as much as possible. Keys should be configured in one place, for all programs. Finally, remember the most consistent interface, one of the few constants throughout the history of computing - the text screen and keyboard, and the teletypewriter before that. Don't overlook it.
More to come, maybe... :)
"If it's on line, it's a work in progress."
Tom Novelli, 3/4/2000
Metacompilation and Assembly
RETRO 10 and 11 were written in themselves using a metacompiler. I had been fascinated by this idea for a long time and was able to explore it heavily. While I still find it to be a good idea, the way I ended up doing it was problematic.
The biggest issue I faced was that I wanted to do this in one step, where loading the RETRO source would create a new image in place of the old one, switch to the new one, and then load the higher level parts of the language over this. In retrospect, this was a really bad idea.
My earlier design for RETRO was very flexible. I allowed almost everything to be swapped out or extended at any time. This made it extremely easy to customize the language and environment, but made it crucial to keep track of what was in memory and what had been patched so that the metacompiler wouldn't refer to anything in the old image during the relocation and control change. It was far too easy to make a mistake, discover that elements of the new image were broken, and then have to go and revert many changes to try to figure out what went wrong.
This was also complicated by the fact that I built new images as I worked, and, while a new image could be built from the last built one, it wasn't always possible to build a new image from the prior release version. (Actually, it was often worse - I failed to check in every change as I went, so often even the prior commits couldn't rebuild the latest images).
For RETRO 12 I wanted to avoid this problem, so I decided to go back to writing the kernel ("Rx") in assembly. I actually wrote a Machine Forth dialect to generate the initial assembly, before eventually hand tuning the final results to its current state.
I could (and likely will eventually) write the assembler in RETRO, but the current one is in C, and is built as part of the standard toolchain.
My VM actually has two assemblers. The older one is Naje. This was intended to be fairly friendly to work with, and handles many of the details of packing instructions for the user. Here is an example of a small program in it:
:square
dup
mul
ret
:main
lit 35
lit &square
call
end
The other assembler is Muri. This is a far more minimalistic assembler, but I've actually grown to prefer it. The above example in Muri would become:
i liju....
r main
: square
i dumure..
: main
i lilica..
d 35
r square
i en......
In Muri, each instruction is reduced to two characters, and the
bundlings are listed as part of an instruction bundle (lines
starting with i). This is less readable if you aren't very
familiar with Nga's assembly and packing rules, but allows a
very quick, efficient way of writing assembly for those who are.
I eventually rewrote the kernel in the Muri style as it's what I prefer, and since there's not much need to make changes in it.
The Path to Self Hosting
RETRO is an image based Forth system running on a lightweight virtual machine. This is the story of how that image is made.
The first RETRO to use an image based approach was RETRO 10. The earliest images were built using a compiler written in Toka, an earlier experimental stack language I had written. It didn't take long to want to drop the dependency on Toka, so I rewrote the image compiler in RETRO and then began development at a faster pace.
RETRO 11 was built using the last RETRO 10 image and an evolved version of the metacompiler. This worked well, but I eventually found it to be problematic.
One of the issues I faced was the inability to make a new image from the prior stable release. Since I develop and test changes incrementally, I reached a point where the current metacompiler and image required each other. This wasn't a fatal flaw, but it was annoying.
Perhaps more critical was the fragility of the system. In R11 small mistakes could result in a corrupt image. The test suite helped identify some of these, but there were a few times I was forced to dig back through the version control history to recover a working image.
The fragile nature was amplified by some design decisions. In R11, after the initial kernel was built, it would be moved to memory address 0, then control would jump into the new kernel to finish building the higher level parts.
Handling this was a tricky task. In R11 almost everything could be revectored, so the metacompiler had to ensure that it didn't rely on anything in the old image during the move. This caused a large number of issues over R11's life.
So on to RETRO 12. I decided that this would be different.
First, the kernel would be assembly, with an external tool
to generate the core image. The kernel is in Rx.md and the
assembler is Muri. To load the standard library, I wrote a
second tool, retro-extend. This separation has allowed me
many fewer headaches as I can make changes more easily and
rebuild from scratch when necessary.
But I miss self-hosting. So last fall I decided to resolve this. And today I'm pleased to say that it is now done.
There are a few parts to this.
Unu. I use a Markdown variation with fenced code blocks.
The tool I wrote in C to extract these is called unu. For
a self hosting RETRO, I rewrote this as a combinator that
reads in a file and runs another word against each line in the
file. So I could display the code block contents by doing:
'filename [ s:put nl ] unu
This made it easier to implement the other tools.
Muri. This is my assembler. It's minimalistic, fast, and
works really well for my purposes. RETRO includes a runtime
version of this (using as{, }as, i, d, and r), so
all I needed for this was to write a few words to parse the
lines and run the corresponding runtime words. As with the C
version, this is a two pass assembler.
Muri generates a new ngaImage with the kernel. To create a
full image I needed a way to load in the standard library and
I/O extensions.
This is handled by retro-extend. This is where it gets more complex. I implemented the Nga virtual machine in RETRO to allow this to run the new image in isolation from the host image. The new ngaImage is loaded, the interpreter is located, and each token is passed to the interpreter. Once done, the new image is written to disk.
So at this point I'm pleased to say that I can now develop RETRO using only an existing copy of RETRO (VM+image) and tools (unu, muri, retro-extend, and a line oriented text editor) written in RETRO.
This project has delivered some additional side benefits. During the testing I was able to use it to identify a few bugs in the I/O extensions, and the Nga-in-RETRO will replace the older attempt at this in the debugger, allowing a safer testing environment.
What issues remain?
The extend process is slow. On my main development server (Linode 1024, OpenBSD 6.4, 64-bit) it takes a bit over five minutes to complete loading the standard library, and a few additional depending on the I/O drivers selected.
Most of the performance issues come from running Nga-in-RETRO to isolate the new image from the host one. It'd be possible to do something a bit more clever (e.g., running a RETRO instance using the new image via a subprocess and piping in the source, or doing relocations of the data), but this is less error prone and will work on all systems that I plan to support (including, with a few minor adjustments, the native hardware versions [assuming the existance of mass storage]).
Sources:
Unu
- http://forth.works/c8820f85e0c52d32c7f9f64c28f435c0
- gopher://forth.works/0/c8820f85e0c52d32c7f9f64c28f435c0
Muri
- http://forth.works/09d6c4f3f8ab484a31107dca780058e3
- gopher://forth.works/0/09d6c4f3f8ab484a31107dca780058e3
retro-extend
- http://forth.works/c812416f397af11db58e97388a3238f2
- gopher://forth.works/0/c812416f397af11db58e97388a3238f2
Prefixes as a Language Element
A big change in RETRO 12 was the elimination of the traditional
parser from the language. This was a sacrifice due to the lack
of an I/O model. RETRO has no way to know how input is given
to the interpret word, or whether anything else will ever be
passed into it.
And so interpret operates only on the current token. The core
language does not track what came before or attempt to guess at
what might come in the future.
This leads into the prefixes. RETRO 11 had a complicated system
for prefixes, with different types of prefixes for words that
parsed ahead (e.g., strings) and words that operated on the
current token (e.g., @). RETRO 12 eliminates all of these in
favor of just having a single prefix model.
The first thing interpret does is look to see if the first
character in a token matches a prefix: word. If it does, it
passes the rest of the token as a string pointer to the prefix
specific handler to deal with. If there is no valid prefix
found, it tries to find it in the dictionary. Assuming that it
finds the words, it passes the d:xt field to the handler that
d:class points to. Otherwise it calls err:notfound.
This has an important implication: words can not reliably have names that start with a prefix character.
It also simplifies things. Anything that would normally parse
becomes a prefix handler. So creating a new word? Use the :
prefix. Strings? Use '. Pointers? Try &. And so on. E.g.,
In ANS | In RETRO
: foo ... ; | :foo ... ;
' foo | &foo
: bar ... ['] foo ; | :bar ... &foo ;
s" hello world!" | 'hello_world!
If you are familiar with ColorForth, prefixes are a similar idea to colors, but can be defined by the user as normal words.
After doing this for quite a while I rather like it. I can see why Chuck Moore eventually went towards ColorForth as using color (or prefixes in my case) does simplify the implementation in many ways.
On The Kernel Wordset
In implementing the RETRO 12 kernel (called Rx) I had to decide on what functionality would be needed. It was important to me that this be kept clean and minimalistic, as I didn't want to spend a lot of time changing it as time progressed. It's far nicer to code at the higher level, where the RETRO language is functional, as opposed to writing more assembly code.
So what made it in?
Primitives
These are words that map directly to Nga instructions.
dup drop swap call eq? -eq? lt? gt?
fetch store + - * /mod and or
xor shift push pop 0;
Memory
fetch-next store-next , s,
Strings
s:to-number s:eq? s:length
Flow Control
choose if -if repeat again
Compiler & Interpreter
Compiler Heap ; [ ] Dictionary
d:link d:class d:xt d:name d:add-header
class:word class:primitive class:data class:macro
prefix:: prefix:# prefix:& prefix:$
interpret d:lookup err:notfound
Assembler
i d r
I could slightly reduce this. The $ prefix could be defined in
higher level code, and I don't strictly need to expose the
fetch-next and store-next here. But since the are already
implemented as dependencies of the words in the kernel, it would
be a bit wasteful to redefine them later in higher level code.
A recent change was the addition of the assembler into the kernel. This allows the higher levels to use assembly as needed, which gives more flexibility and allows for more optimal code in the standard library.
With these words the rest of the language can be built up. Note that the Rx kernel does not provide any I/O words. It's assumed that the RETRO interfaces will add these as best suited for the systems they run on.
There is another small bit. All images start with a few key pointers in fixed offsets of memory. These are:
| Offset | Contains |
| ------ | --------------------------- |
| 0 | lit call nop nop |
| 1 | Pointer to main entry point |
| 2 | Dictionary |
| 3 | Heap |
| 4 | RETRO version identifier |
An interface can use the dictionary pointer and knowledge of the
dictionary format for a specific RETRO version to identify the
location of essential words like interpret and err:notfound
when implementing the user facing interface.
On The Evolution Of Ngaro Into Nga
When I decided to begin work on what became RETRO 12, I knew the process would involve updating Ngaro, the virtual machine that RETRO 10 and 11 ran on.
Ngaro rose out of an earlier experimental virtual machine I had written back in 2005-2006. This earlier VM, called Maunga, was very close to what Ngaro ended up being, though it had a very different approach to I/O. (All I/O in Maunga was intended to be memory mapped; Ngaro adopted a port based I/O system).
Ngaro itself evolved along with RETRO, gaining features like automated skipping of NOPs and a LOOP opcode to help improve performance. But the I/O model proved to be a problem. When I created Ngaro, I had the idea that I would always be able to assume a console/terminal style environment. The assumption was that all code would be entered via the keyboard (or maybe a block editor), and that proved to be the fundamental flaw as time went on.
As RETRO grew it was evident that the model had some serious problems. Need to load code from a file? The VM and language had functionality to pretend it was being typed in. Want to run on something like a browser, Android, or iOS? The VM would need to be implemented in a way that simulates input being typed into the VM via a simulated keyboard. And RETRO was built around this. I couldn't change it because of a promise to maintain, as much as possible, source compatibility for a period of at least five years.
When the time came to fix this, I decided at the start to keep the I/O model separate from the core VM. I also decided that the core RETRO language would provide some means of interpreting code without requiring an assumption that a traditional terminal was being used.
So Nga began. I took the opportunity to simplify the instruction set to just 26 essential instructions, add support for packing multiple instructions per memory location (allowing a long due reduction in memory footprint), and to generally just make a far simpler design.
I've been pleased with Nga. On its own it really isn't useful though. So with RETRO I embed it into a larger framework that adds some basic I/O functionality. The interfaces handle the details of passing tokens into the language and capturing any output. They are free to do this in whatever model makes most sense on a given platform.
So far I've implemented:
- a scripting interface, reading input from a file and
offering file i/o, gopher, and reading from stdin, and
sending output to stdout.
- an interactive interface, built around ncurses, reading
input from stdin, and displaying output to a scrolling
buffer.
- an iOS interface, built around a text editor, directing
output to a separate interface pane.
- an interactive block editor, using a gopher-based block
data store. Output is displayed to stdout, and input is
done via the blocks being evaluated or by reading from
stdin.
In all cases, the only common I/O word that has to map to an
exposed instruction is putc, to display a single character to
some output device. There is no requirement for a traditional
keyboard input model.
By doing this I was able to solve the biggest portability issue with the RETRO 10/11 model, and make a much simpler, cleaner language in the end.
RETRO 11 (2011 - 2019): A Look Back
So it's now been about five years since the last release of RETRO 11. While I still see some people obtaining and using it, I've moved on to the twelth generation of RETRO. It's time for me to finally retire RETRO 11.
As I prepare to do so, I thought I'd take a brief look back.
RETRO 11 began life in 2011. It grew out of RETRO 10, which was the first version of RETRO to not be written in x86 assembly language. For R10 and R11, I wrote a portable virtual machine (with numerous implementations) and the Forth dialect was kept in an image file which ran on the VM.
RETRO 10 worked, but was always a bit too sloppy and changed drastically between releases. The major goal of RETRO 11 was to provide a stable base for a five year period. In retrospect, this was mostly achieved. Code from earlier releases normally needed only minor adjustments to run on later releases, though newer releases added significantly to the language.
There were seven releases.
- Release 11.0: 2011, July
- Release 11.1: 2011, November
- Release 11.2: 2012, January
- Release 11.3: 2012, March
- Release 11.4: 2012, July
- Release 11.5: 2013, March
- Release 11.6: 2014, August
Development was fast until 11.4. This was the point at which I had to slow down due to RSI problems. It was also the point which I started experiencing some problems with the metacompiler (as discussed previously).
RETRO 11 was flexible. All colon definitions were setup as hooks, allowing new functionality to be layered in easily. This allowed the later releases to add things like vocabularies, search order, tab completion, and keyboard remapping. This all came at a cost though: later things could use the hooks to alter behavior of existing words, so it was necessary to use a lot of caution to ensure that the layers didn't break the earlier code.
The biggest issue was the I/O model. RETRO 11 and the Ngaro VM assumed the existence of a console environment. All input was required to be input at the keyboard, and all output was to be shown on screen. This caused some problems. Including code from a file required some tricks, temporarily rewriting the keyboard input function to read from the file. It also became a major issue when I wrote the iOS version. The need to simulate the keyboard and console complicated everything and I had to spend a considerable amount of effort to deal with battery performance resulting from the I/O polling and wait states.
But on the whole it worked well. I used RETRO 11.6 until I started work on RETRO 12 in late 2016, and continued running some tools written in R11 until the first quarter of last year.
The final image file was 23,137 cells (92,548 bytes). This was bloated by keeping some documentation (stack comments and short descriptions) in the image, which started in 11.4. This contained 269 words.
I used RETRO 11 for a wide variety of tasks. A small selection of things that were written includes:
- a pastebin
- front end to ii (irc client)
- small explorations of interactive fiction
- irc log viewer
- tool to create html from templates
- tool to automate creation of an SVCD from a set of photos
- tools to generate reports from data sets for my employer
In the end, I'm happy with how RETRO 11 turned out. I made some mistakes in embracing too much complexity, but despite this it was a successful system for many years.
Security Concerns
The standard RETRO is not a good choice for applications needing to be highly secure.
Runtime Checks
The RETRO system performs only minimal checks. It will not load an image larger than the max set at build time. And stack over/underflow are checked for as code executes.
The system does not attempt to validate anything else, it's quite easy to crash.
Isolation
The VM itself and the core code is self contained. Nga does not make use of malloc/free, and uses only standard system libraries. It's possible for buffer overruns within the image (overwriting Nga code), but the RETRO image shouldn't leak into the C portions.
I/O presents a bigger issue. Anything involving I/O, especially
with the unix: words, may be a vector for attacks.
Future Direction
I'm not planning to add anything to the image side as, for me, the performance hit due to added checks is bigger than the benefits.
The story is different on the VM side. I've already begun taking steps to address some of the issues, using functions that check for overruns with strings and doing some minor testing for these conditions. I will be gradually addressing the various I/O related extensions, though it's unlikely to ever be fully guarded against attacks.
Rationale
RETRO is, primarily, a personal system. I'm running code I wrote to solve problems I face. On the occasions where I run code sent to me by others, I read it carefully first and then run inside a sandboxed environment if I'm worried about anything in it.
On The Use Of Underscores In Word Names
In brief: don't use underscores in word names.
There is a good reason for this, and it has to do with how RETRO
processes strings. By default, underscores in strings are replaced
by spaces. This is problematic when dealing with words like var,
const, and d:create which take word names as strings.
Consider:
:hello_msg 'hello_user ;
'test_name var
#188 !test_name
In the first case, the : prefix handles the token, so the
underscore is not remapped to a space, creating a word name as
hello_msg. But in the second, the ' prefix remaps the
underscore to a space, giving a variable name of test name.
In the third line, the name lookup will fail as test_name is
not defined, so the store will be done to an incorrect address.
Because of this, it's best to avoid underscores in names.
Having covered this, if you do need to use them for some reason,
you can replace d:add-header with a version that remaps spaces
back to underscores before creating the header. The following
will allow for this.
~~~
{{
:fields @Dictionary , (link) , (xt) , (class) ;
:invalid-name? dup ASCII:SPACE s:contains-char? ;
:rewrite [ ASCII:SPACE [ $_ ] case ] s:map ;
:entry here &call dip !Dictionary ;
[ [ fields invalid-name? &rewrite if s, (name) ] entry ]
}}
#1793 &d:add-header store
&d:add-header n:inc store
~~~
Additional Note:
Some version of RETRO have included the above patch. The last
release that will include this by default is 2020.4 as it is
not needed by the majority of users. If you want to keep it in
your system, you will need to load it yourself or add it to
your package/list.forth (for Unix users) before building.
The Code It Yourself Manifesto
We use software for our everyday needs because we want to get something done. We have goals to achieve and things to do.
The software we use is coded by brave programmers that have their own goals. Most of the time there is an overlap between their goals and ours.
Over time these will diverge.
This means that the tools we depend on grow features we don't use or understand. There will be bugs in these code parts which will prevent us from reaching our goals.
So we are at a fork in the road:
- We have the choice of trying to understand the code and fix it.
- We have the choice of trying another program, whose creator's goals are closer to ours.
- We also have the choice of coding the software ourself.
All but the last path mean endless seeking, evaluating and further deviation from our goals. Therefore we replace programs we do not understand fully with our own implementation.
The followers of the Code It Yourself Manifesto believe in these things:
- We implement it according to our own goals.
- We make mistakes and learn from them.
- We learn how our tools we depend on need to work.
- We gain a deep understanding of our problem domain.
- We still embrace sharing of ideas and code.
Sharing is only possible if we are excellent developers to each other. The next developer reading our code will be us in a not so distant future. Coding It Ourselves means we will document our code, clearly stating the goal of the software we write.
Together we enjoy the diversity of implementations and ideas.
We encourage our colleagues to
Code It Yourself.
Written by Christian Kellermann on 2016-01-12, licensed under a CreativeCommonsAttribution-ShareAlike3.0UnportedLicense.
Original text taken from http://pestilenz.org/~ckeen/blog/posts/ciy-manifesto.html
Deprecation Policy
As RETRO evolves, some words will become obsolete and no longer be needed. In each release, these will be marked as deprecated in the glossary. Any deprecated words will be removed in the next quarterly release.
E.g., if 2020.1 had deprecated words, these would be removed in the 2020.4 release. Any words made deprecated in between 2020.1 and 2020.4 would be removed in the 2020.7 release.