____ _ _ || \\ \\ // ||_// )x( || \\ // \\ 2019.12 a minimalist forth for nga *Rx* (*retro experimental*) is a minimal Forth implementation for the Nga virtual machine. Like Nga this is intended to be used within a larger supporting framework adding I/O and other desired functionality. ## General Notes on the Source Rx is developed using a literate tool called *unu*. This allows easy extraction of fenced code blocks into a separate file for later compilation. I've found the use of a literate style to be very beneficial as it makes it easier for me to keep the code and commentary in sync, and helps me to approach development in a more structured manner. This source is written in Muri, an assembler for Nga. Before going on, I should explain a bit about Nga and Muri. Nga provides a MISC inspired virtual machine for a dual stack architecture. There are 27 instructions, with up to four packed into each memory location (*cell*). The instructions are: 0 nop 7 jump 14 gt 21 and 1 lit 8 call 15 fetch 22 or 2 dup 9 ccall 16 store 23 xor 3 drop 10 return 17 add 24 shift 4 swap 11 eq 18 sub 25 zret 5 push 12 neq 19 mul 26 end 6 pop 13 lt 20 divmod I won't explain them here, but if you're familiar with Forth, it should be pretty easy to figure out. Packing of instructions lets me save space, but does require a little care. Instructions that modify the instruction pointer should be followed by NOP. These are: JUMP, CALL, CCALL, RETURN, and ZRET. Additionally, if the instruction bundle contains a LIT, a value must be in the following cell. (One for each LIT in the bundle) The reason for this relates to how Nga processes the opcodes. To illustrate, assume a stack with a couple of values: #1 #2 And a function that consumes two values before returning a some new ones: :function * #3 ; If we were to use an instruction bundle like: lit call add nop function Nga will: (1) push a pointer to the function to the stack (2) setup a call to the function (3) add the top values on the stack (#1 #2), leaving a single value (#3) (4) do nothing At this point the bundle is done, so control goes to the called function. But we now have only one value on the stack, so the stack underflows and Nga will crash. It's not forbidden, and this can be useful to improve code density, but exercise caution and be sure to keep track of this behavior to avoid hard to identify bugs. Muri uses the first two characters of each instruction name when composing the bundles, with NOP being named as two dots. So: lit lit add nop Is a bundle named: liliad.. And with two `li` instructions, must be followed by two values. Muri uses a directive in the first line to tell it what to expect. Directives are: i instruction bundle d decimal value r reference to label : label s zero terminated string ## In the Beginning... Nga expects code to start with a jump to the main entry point. Rx doesn't really have a main entry point (the top level loop is assumed to be part of the interface layer), but I allocate the space for a jump here anyway. This makes it possible to patch the entry point later, if using an interface that adds the appropriate I/O functionality. ~~~ i liju.... d -1 ~~~ With this, it's time to allocate some data elements. These are always kept in known locations after the initial jump to ensure that they can be easily identified and interfaced with external tools. This is important as Nga allows for a variety of I/O models to be implemented and I don't want to tie Rx into any one specific model. Here's the initial memory map: | Offset | Contains | | ------ | --------------------------- | | 0 | lit call nop nop | | 1 | Pointer to main entry point | | 2 | Dictionary | | 3 | Heap | | 4 | RETRO version | ~~~ : Dictionary r 9999 : Heap d 1536 : Version d 201912 ~~~ Both of these are pointers. `Dictionary` points to the most recent dictionary entry. (See the *Dictionary* section at the end of this file.) `Heap` points to the next free address. This is hard coded to an address beyond the end of the Rx kernel. I adjust this as needed if the kernel grows or shinks significantly. See the *Interpreter & Compiler* section for more on this. ## Nga Instruction Set As mentioned earlier, Nga provides 27 instructions. Rx begins the actual coding by assigning each to a separate function. These are not intended for direct use; the compiler will fetch the opcode values to use from these functions when compiling. Many will also be exposed in the initial dictionary. ~~~ : _nop d 0 i re...... : _lit d 1 i re...... : _dup d 2 i re...... : _drop d 3 i re...... : _swap d 4 i re...... : _push d 5 i re...... : _pop d 6 i re...... : _jump d 7 i re...... : _call d 8 i re...... : _ccall d 9 i re...... : _ret d 10 i re...... : _eq d 11 i re...... : _neq d 12 i re...... : _lt d 13 i re...... : _gt d 14 i re...... : _fetch d 15 i re...... : _store d 16 i re...... : _add d 17 i re...... : _sub d 18 i re...... : _mul d 19 i re...... : _divmod d 20 i re...... : _and d 21 i re...... : _or d 22 i re...... : _xor d 23 i re...... : _shift d 24 i re...... : _zret d 25 i re...... : _end d 26 i re...... ~~~ Though Nga allows for multiple instructions to be packed into a single memory location (called a *cell*), Rx only packs a few specific combinations. Since calls and jumps take a value from the stack, a typical call (in Muri assembly) would look like: i lica.... r bye Without packing this takes three cells: one for the lit, one for the address, and one for the call. Packing drops it to two since the lit/call combination can be fit into a single cell. Likewise, I use a packed jump for use with quotations. These saves several hundred cells (and thus fetch/decode cycles) when loading the standard library. The raw values for these are: 2049 lica.... 1793 liju.... These are hardcoded in a few places later. I had previously used a lookup, but this proved costly in processing time, so hard coding proved better. (These places are clearly marked) ## Memory Memory is a big, flat, linear array. The addressing starts at zero and counts upwards towards a fixed upper limit (set by the VM). The basic memory accesses are handled via `fetch` and `store`. The next two functions provide easier access to sequences of data by fetching or storing a value and returning the next address. `fetch-next` takes an address and fetches the stored value. It returns the next address and the stored value. ~~~ : fetch-next i duliadsw d 1 i fere.... ~~~ `store-next` takes a value and an address. It stores the value to the address and returns the next address. ~~~ : store-next i duliadpu d 1 i stpore.. ~~~ ## Conditionals The Rx kernel provides three conditional forms: flag true-pointer false-pointer choose flag true-pointer if flag false-pointer -if `choose` is a conditional combinator which will execute one of two functions, depending on the state of a flag. I use a little hack here. I store the pointers into a jump table with two fields, and use the flag as the index. Defaults to the *false* entry, since a *true* flag is -1. Note that this requires that the flags be -1 (for TRUE) and 0 (for FALSE). It's possible to make this more flexible, but at a significant performance hit, so I'm leaving it this way. ~~~ : choice:true d 0 : choice:false d 0 : choose i listlist r choice:false r choice:true i liadfeca r choice:false i re...... ~~~ Next the two *if* forms. Note that `-if` falls into `if`. This saves two cells of memory. ~~~ : -if i pulieqpo d 0 : if i cc...... i re...... ~~~ ## Strings The kernel needs two basic string operations for dictionary searches: obtaining the length and comparing for equality. Strings in Rx are zero terminated. This is a bit less elegant than counted strings, but the implementation is quick and easy. First up, string length. The process here is trivial: * Make a copy of the starting point * Fetch each character, comparing to zero * If zero, break the loop * Otherwise discard and repeat * When done subtract the original address from the current one * Then subtract one (to account for the zero terminator) ~~~ : count i lica.... r fetch-next i zr...... i drliju.. r count : s:length i dulica.. r count i lisuswsu d 1 i re...... ~~~ String comparisons are harder. In high level code this is: dup fetch push n:inc swap dup fetch push n:inc pop dup pop -eq? [ drop-pair drop #0 pop pop drop drop ] [ 0; drop s:eq? pop pop drop drop ] choose drop-pair #-1 ; I've rewritten this a few times. The current implementation is fast enough, and not overly long. It may be worth looking into a hash based comparsion in the future. ~~~ : mismatch i drdrdrli d 0 i popodrdr i re...... : matched i zr...... i drlica.. r s:eq i popodrdr i re...... : s:eq i dufepuli d 1 i adswdufe i puliadpo d 1 i duponeli r mismatch i lilica.. r matched r choose i drdrlire d -1 ~~~ ## Interpreter & Compiler ### Compiler Core The heart of the compiler is `comma` which stores a value into memory and increments a variable (`Heap`) pointing to the next free address. ~~~ : comma i lifelica r Heap r store-next i listre.. r Heap ~~~ I also add a couple of additional forms. `comma:opcode` is used to compile VM instructions into the current defintion. This is where those functions starting with an underscore come into play. Each wraps a single instruction. Using this I can avoid hard coding the opcodes. This performs a jump to the `comma` word instead of using a `call/ret` to save a cell and slightly improve performance. I will use this technique frequently. ~~~ : comma:opcode i feliju.. r comma ~~~ `comma:string` is used to compile a string into the current definition. As with `comma:opcode`, this uses a `jump` to eliminate the final tail call. :($) fetch-next 0; , ($) ; :s, ($) drop 0 , ; ~~~ : ($) i lica.... r fetch-next i zr...... i lica.... r comma i liju.... r ($) : comma:string i lica.... r ($) i drliliju d 0 r comma ~~~ With the core functions above it's now possible to setup a few more things that make compilation at runtime more practical. First, a variable indicating whether we should compile or run a function. In traditional Forth this would be **STATE**; I call it `Compiler`. This will be used by the *word classes*. ~~~ : Compiler d 0 ~~~ Next is *semicolon*; which compiles the code to terminate a function and sets the `Compiler` to an off state (0). This just needs to compile in a RET. ~~~ : ; i lilica.. r _ret r comma:opcode i lilistre d 0 r Compiler ~~~ ### Word Classes Rx is built over the concept of *word classes*. Word classes are a way to group related words, based on their compilation and execution behaviors. A *class handler* function is defined to handle an execution token passed to it on the stack. Rx provides several classes with differing behaviors: `class:data` provides for dealing with data structures. | interpret | compile | | -------------------- | ----------------------------- | | leave value on stack | compile value into definition | ~~~ : class:data i lifezr.. r Compiler i drlilica r _lit r comma:opcode i liju.... r comma ~~~ `class:word` handles most functions. | interpret | compile | | -------------------- | ----------------------------- | | call a function | compile a call to a function | ~~~ : class:word:interpret i ju...... : class:word:compile i lilica.. d 2049 r comma i liju.... r comma : class:word i lifelili r Compiler r class:word:compile r class:word:interpret i liju.... r choose ~~~ `class:primitive` is a special class handler for functions that correspond to Nga instructions. | interpret | compile | | -------------------- | ------------------------------------ | | call the function | compile an instruction | ~~~ : class:primitive i lifelili r Compiler r comma:opcode r class:word:interpret i liju.... r choose ~~~ `class:macro` is the class handler for *compiler macros*. These are functions that always get called. They can be used to extend the language in interesting ways. | interpret | compile | | -------------------- | ----------------------------- | | call the function | call the function | ~~~ : class:macro i ju...... ~~~ The class mechanism is not limited to these classes. You can write custom classes at any time. On entry the custom handler should take the XT passed on the stack and do something with it. Generally the handler should also check the `Compiler` state to determine what to do in either interpretation or compilation. ### Dictionary Rx has a single dictionary consisting of a linked list of headers. The current form of a header is shown in the chart below. | field | holds | accessor | | ----- | ---------------------------------- | -------- | | link | link to the previous entry | d:link | | xt | link to start of the function | d:xt | | class | link to the class handler function | d:class | | name | zero terminated string | d:name | The initial dictionary is constructed at the end of this file. It'll take a form like this: : 0000 d 0 r _dup r class:primitive s dup : 0001 r 0000 r _drop r class:primitive s drop : 0002 r 0001 r _swap r class:primitive s swap Each entry starts with a pointer to the prior entry (with a pointer to zero marking the first entry in the dictionary), a pointer to the start of the function, a pointer to the class handler, and a null terminated string indicating the name exposed to the Rx interpreter. Rx stores the pointer to the most recent entry in a variable called `Dictionary`. For simplicity, I just assign the last entry an arbitrary label of 9999. This is set at the start of the source. (See *In the Beginning...*) Rx provides accessor functions for each field. Since the number of fields (or their ordering) may change over time, using these reduces the number of places where field offsets are hard coded. ~~~ : d:link i re...... : d:xt i liadre.. d 1 : d:class i liadre.. d 2 : d:name i liadre.. d 3 ~~~ A traditional Forth has `create` to make a new dictionary entry pointing to the next free location in `Heap`. Rx has `d:add-header` which serves as a slightly more flexible base. You provide a string for the name, a pointer to the class handler, and a pointer to the start of the function. Rx does the rest. In actual practice, I never use this outside of Rx. New words are made using the `:` prefix, or `d:create` (once defined in the standard library). At some point I may simplify this by moving `d:create` into Rx and using it in place of `d:add-header`. ~~~ : d:add-header i lifepuli r Heap r Dictionary i felica.. r comma i lica.... r comma i lica.... r comma i lica.... r comma:string i polistre r Dictionary ~~~ Rx doesn't provide a traditional create as it's designed to avoid assuming a normal input stream and prefers to take its data from the stack. ### Dictionary Search ~~~ : Which d 0 : Needle d 0 : found i listlire r Which r _nop : find i lilistli d 0 r Which r Dictionary i fe...... : find_next i zr...... i dulica.. r d:name i lifelica r Needle r s:eq i licc.... r found i feliju.. r find_next : d:lookup i listlica r Needle r find i lifere.. r Which ~~~ ### Number Conversion This code converts a zero terminated string into a number. The approach is very simple: * Store an internal multiplier value (-1 for negative, 1 for positive) * Clear an internal accumulator value * Loop: * Fetch the accumulator value * Multiply by 10 * For each character, convert to a numeric value and add to the accumulator * Store the updated accumulator * When done, take the accumulator value and the modifier and multiply them to get the final result Rx only supports decimal numbers. If you want more bases, it's pretty easy to add them later, but it's not needed in the base kernel. ~~~ : next i lica.... r fetch-next i zr...... i lisuswpu d 48 i swlimuad d 10 i poliju.. r next : check i dufelieq d 45 i zr...... i drswdrli d -1 i swliadre d 1 : s:to-number i liswlica d 1 r check i liswlica d 0 r next i drmure.. ~~~ ### Token Processing An input token has a form like: string Rx will check the first character to see if it matches a known prefix. If it does, it will pass the string (sans prefix) to the prefix handler. If not, it will attempt to find the token in the dictionary. Prefixes are handled by functions with specific naming conventions. A prefix name should be: prefix: Where is the character for the prefix. These are compiler macros (using the `class:macro` class) and watch the `Compiler` to decide how to deal with the token. To find a prefix, Rx stores the prefix character into a string named `prefixed`. It then searches for this string in the dictionary. If found, it sets an internal variable (`prefix:handler`) to the dictionary entry for the handler function. If not found, `prefix:handler` is set to zero. The check, done by `prefix?`, also returns a flag. ~~~ : prefix:no d 32 d 0 : prefix:handler d 0 : prefixed s prefix:_ : prefix:prepare i feliliad r prefixed d 7 i stre.... : prefix:has-token? i dulica.. r s:length i lieqzr.. d 1 i drdrlire r prefix:no : prefix? i lica.... r prefix:has-token? i lica.... r prefix:prepare i lilica.. r prefixed r d:lookup i dulistli r prefix:handler d 0 i nere.... ~~~ Rx makes extensive use of prefixes for implementing major parts of the language, including parsing numbers (prefix with `#`), obtaining pointers (prefix with `&`), and defining functions (using the `:` prefix). | prefix | used for | example | | ------ | ----------------- | ------- | | # | numbers | #100 | | $ | ASCII characters | $e | | & | pointers | &swap | | : | definitions | :foo | | ( | Comments | (n-) | :prefix:( (s-) drop ; ~~~ : prefix:( i drre.... ~~~ :prefix:# (s-n) s:to-number class:data ; ~~~ : prefix:# i lica.... r s:to-number i liju.... r class:data ~~~ :prefix:$ (s-c) fetch class:data ; ~~~ : prefix:$ i feliju.. r class:data ~~~ :prefix:: (s-) &class:word &Heap fetch d:add-header &Heap fetch &Dictionary d:xt store #-1 &Compiler store ; ~~~ : prefix:: i lilifeli r class:word r Heap r d:add-header i ca...... i lifelife r Heap r Dictionary i lica.... r d:xt i stlilist d -1 r Compiler i re...... ~~~ The `&` prefix is used to return the address of a named item. This will correspond to the `d:xt` field of the word header. In higher level Retro this would be: :prefix:& (s-a) d:lookup d:xt fetch class:data ; As an example: #1 #2 &+ call (call_`+`_via_pointer) &Heap fetch (fetch_from_`Heap`) In the latter case, the use of `class:data` means that I don't *need* to use the `&` prefix, but I do this anyway as I find it helps to provide a visual clue as to the intent of the code. This is also useful with combinators. If you are only using a single word, using `&word` instead of `[ word ]` will be smaller and faster. For those familiar with traditional Forth, the `&` prefix replaces both `'` and `[']`. ~~~ : prefix:& i lica.... r d:lookup i lica.... r d:xt i feliju.. r class:data ~~~ ### Quotations Quotations are anonymous, nestable blocks of code. Rx uses them for control structures and some aspects of data flow. A quote takes a form like: [ #1 #2 ] #12 [ square #144 eq? [ #123 ] [ #456 ] choose ] call Begin a quotation with `[` and end it with `]`. The code here is slightly complicated by the fact that these have to be nestable, and so must compile the appropriate jumps around the nested blocks, in addition to properly setting and restoring the `Compiler` state. ~~~ : [ i lifeliad r Heap d 2 i lifelili r Compiler d -1 r Compiler i stlilica d 1793 r comma i lifelili r Heap d 0 r comma i ca...... i lifere.. r Heap : ] i lilica.. r _ret r comma:opcode i lifeswli r Heap r _lit i lica.... r comma:opcode i lica.... r comma i swstlist r Compiler i lifezr.. r Compiler i drdrre.. ~~~ ## Lightweight Control Structures Rx provides a couple of functions for simple flow control apart from using quotations. These are `repeat`, `again`, and `0;`. An example of using them: :s:length dup [ repeat fetch-next 0; drop again ] call swap - #1 - ; These can only be used within a definition or quotation. If you need to use them interactively, wrap them in a quote and `call` it. ~~~ : repeat i lifere.. r Heap : again i lilica.. r _lit r comma:opcode i lica.... r comma i liliju.. r _jump r comma:opcode : 0; i liliju.. r _zret r comma:opcode ~~~ I take a brief aside here to implement `push` and `pop`, which move a value to/from the address stack. These are compiler macros. ~~~ : push i liliju.. r _push r comma:opcode : pop i liliju.. r _pop r comma:opcode ~~~ ## Interpreter The *interpreter* is what processes input. What it does is: * Take a string * See if the first character has a prefix handler * Yes: pass the rest of the string to the prefix handler * No: lookup in the dictionary * Found: pass xt of word to the class handler * Not found: report error via `err:notfound` First, the handler for dealing with words that are not found. This is defined here as a jump to the handler for the Nga *NOP* instruction. It is intended that this be hooked into and changed. As an example, in Rx code, assuming an I/O interface with some support for strings and output: [ $? c:put sp 'word_not_found s:put ] &err:notfound #1 + store An interface should either patch the jump, or catch it and do something to report the error. ~~~ : err:notfound i liju.... r _nop i re...... ~~~ `call:dt` takes a dictionary token and pushes the contents of the `d:xt` field to the stack. It then calls the class handler stored in `d:class`. ~~~ : call:dt i dulica.. r d:xt i feswlica r d:class i feju.... ~~~ ~~~ : input:source d 0 : interpret:prefix i lifezr.. r prefix:handler i lifeliad r input:source d 1 i swliju.. r call:dt : interpret:word i lifeliju r Which r call:dt : interpret:noprefix i lifelica r input:source r d:lookup i linelili d 0 r interpret:word r err:notfound i liju.... r choose : interpret i dulistli r input:source r prefix? i ca...... i lililiju r interpret:prefix r interpret:noprefix r choose ~~~ ## The Initial Dictionary This sets up the initial dictionary. Maintenance of this bit is annoying, but it isn't necessary to change this unless you add or remove new functions in the kernel. ~~~ : 0000 d 0 r _dup r class:primitive s dup : 0001 r 0000 r _drop r class:primitive s drop : 0002 r 0001 r _swap r class:primitive s swap : 0003 r 0002 r _call r class:primitive s call : 0004 r 0003 r _eq r class:primitive s eq? : 0005 r 0004 r _neq r class:primitive s -eq? : 0006 r 0005 r _lt r class:primitive s lt? : 0007 r 0006 r _gt r class:primitive s gt? : 0008 r 0007 r _fetch r class:primitive s fetch : 0009 r 0008 r _store r class:primitive s store : 0010 r 0009 r _add r class:primitive s + : 0011 r 0010 r _sub r class:primitive s - : 0012 r 0011 r _mul r class:primitive s * : 0013 r 0012 r _divmod r class:primitive s /mod : 0014 r 0013 r _and r class:primitive s and : 0015 r 0014 r _or r class:primitive s or : 0016 r 0015 r _xor r class:primitive s xor : 0017 r 0016 r _shift r class:primitive s shift : 0018 r 0017 r push r class:macro s push : 0019 r 0018 r pop r class:macro s pop : 0020 r 0019 r 0; r class:macro s 0; : 0021 r 0020 r fetch-next r class:word s fetch-next : 0022 r 0021 r store-next r class:word s store-next : 0023 r 0022 r s:to-number r class:word s s:to-number : 0024 r 0023 r s:eq r class:word s s:eq? : 0025 r 0024 r s:length r class:word s s:length : 0026 r 0025 r choose r class:word s choose : 0027 r 0026 r if r class:primitive s if : 0028 r 0027 r -if r class:word s -if : 0029 r 0028 r prefix:( r class:macro s prefix:( : 0030 r 0029 r Compiler r class:data s Compiler : 0031 r 0030 r Heap r class:data s Heap : 0032 r 0031 r comma r class:word s , : 0033 r 0032 r comma:string r class:word s s, : 0034 r 0033 r ; r class:macro s ; : 0035 r 0034 r [ r class:macro s [ : 0036 r 0035 r ] r class:macro s ] : 0037 r 0036 r Dictionary r class:data s Dictionary : 0038 r 0037 r d:link r class:word s d:link : 0039 r 0038 r d:xt r class:word s d:xt : 0040 r 0039 r d:class r class:word s d:class : 0041 r 0040 r d:name r class:word s d:name : 0042 r 0041 r class:word r class:word s class:word : 0043 r 0042 r class:macro r class:word s class:macro : 0044 r 0043 r class:data r class:word s class:data : 0045 r 0044 r d:add-header r class:word s d:add-header : 0046 r 0045 r prefix:# r class:macro s prefix:# : 0047 r 0046 r prefix:: r class:macro s prefix:: : 0048 r 0047 r prefix:& r class:macro s prefix:& : 0049 r 0048 r prefix:$ r class:macro s prefix:$ : 0050 r 0049 r repeat r class:macro s repeat : 0051 r 0050 r again r class:macro s again : 0052 r 0051 r interpret r class:word s interpret : 0053 r 0052 r d:lookup r class:word s d:lookup : 0054 r 0053 r class:primitive r class:word s class:primitive : 0055 r 0054 r Version r class:data s Version : 9999 r 0055 r err:notfound r class:word s err:notfound ~~~ ## Appendix: Words, Stack Effects, and Usage | Word | Stack | Notes | | --------------- | --------- | ------------------------------------------------- | | dup | n-nn | Duplicate the top item on the stack | | drop | nx-n | Discard the top item on the stack | | swap | nx-xn | Switch the top two items on the stack | | call | p- | Call a function (via pointer) | | eq? | nn-f | Compare two values for equality | | -eq? | nn-f | Compare two values for inequality | | lt? | nn-f | Compare two values for less than | | gt? | nn-f | Compare two values for greater than | | fetch | p-n | Fetch a value stored at the pointer | | store | np- | Store a value into the address at pointer | | + | nn-n | Add two numbers | | - | nn-n | Subtract two numbers | | * | nn-n | Multiply two numbers | | /mod | nn-mq | Divide two numbers, return quotient and remainder | | and | nn-n | Perform bitwise AND operation | | or | nn-n | Perform bitwise OR operation | | xor | nn-n | Perform bitwise XOR operation | | shift | nn-n | Perform bitwise shift | | fetch-next | a-an | Fetch a value and return next address | | store-next | na-a | Store a value to address and return next address | | push | n- | Move value from data stack to address stack | | pop | -n | Move value from address stack to data stack | | 0; | n-n OR n- | Exit word (and `drop`) if TOS is zero | | s:to-number | s-n | Convert a string to a number | | s:eq? | ss-f | Compare two strings for equality | | s:length | s-n | Return length of string | | choose | fpp-? | Execute *p1* if *f* is -1, or *p2* if *f* is 0 | | if | fp-? | Execute *p* if flag *f* is true (-1) | | -if | fp-? | Execute *p* if flag *f* is false (0) | | Compiler | -p | Variable; holds compiler state | | Heap | -p | Variable; points to next free memory address | | , | n- | Compile a value into memory at `here` | | s, | s- | Compile a string into memory at `here` | | ; | - | End compilation and compile a *return* instruction| | [ | - | Begin a quotation | | ] | - | End a quotation | | Dictionary | -p | Variable; points to most recent header | | d:link | p-p | Given a DT, return the address of the link field | | d:xt | p-p | Given a DT, return the address of the xt field | | d:class | p-p | Given a DT, return the address of the class field | | d:name | p-p | Given a DT, return the address of the name field | | class:word | p- | Class handler for standard functions | | class:primitive | p- | Class handler for Nga primitives | | class:macro | p- | Class handler for immediate functions | | class:data | p- | Class handler for data | | d:add-header | saa- | Add an item to the dictionary | | prefix:# | s- | # prefix for numbers | | prefix:: | s- | : prefix for definitions | | prefix:& | s- | & prefix for pointers | | prefix:$ | s- | $ prefix for ASCII characters | | prefix:( | s- | ( prefix for comments | | repeat | -a | Start an unconditional loop | | again | a- | End an unconditional loop | | interpret | s-? | Evaluate a token | | d:lookup | s-p | Given a string, return the DT (or 0 if undefined) | | Version | -a | Variable; holds a version identifier | | err:notfound | - | Handler for token not found errors | ## Legalities Rx is Copyright (c) 2016-2019, Charles Childers Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. My thanks go out to Michal J Wallace, Luke Parrish, JGL, Marc Simpson, Oleksandr Kozachuk, Jay Skeer, Greg Copeland, Aleksej Saushev, Foucist, Erturk Kocalar, Kenneth Keating, Ashley Feniello, Peter Salvi, Christian Kellermann, Jorge Acereda, Remy Moueza, John M Harrison, and Todd Thomas. All of these great people helped in the development of RETRO 10 and 11, without which Rx wouldn't have been possible.