193 lines
4.3 KiB
Forth
193 lines
4.3 KiB
Forth
# Overview
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RETRO has a significant number of differences from traditional
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Forth systems. This will provide a number of aliases as well as
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words from traditional Forth systems.
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It is not possible to provide a traditional Forth as a superset
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of RETRO due to the way the parsing and token processing works.
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Implementing a traditional Forth using RETRO as the implementation
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language would be possible (within the limits of the Nga virtual
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machine), but I have no desire to do this.
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Where letters are used, I am using uppercase. This is in keeping
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with tradition as well as the minimal requirements of ANS.
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## Memory Access
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~~~
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:@ (a-n) fetch ;
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:! (na-) store ;
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:C@ (a-n) fetch ;
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:C! (na-) store ;
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:@+ (a-an) fetch-next ;
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:!+ (na-a) store-next ;
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~~~
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## Return Stack
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~~~
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:>R (n-) |push ; immediate
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:R> (-n) |pop ; immediate
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:R@ (-n) |pop |dup |push ; immediate
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~~~
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## Conditionals
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~~~
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:IF FALSE |[ ; immediate
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:ELSE |] drop TRUE |[ ; immediate
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:THEN |] [ |choose ] [ |if ] choose ; immediate
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:= eq? ;
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:<> -eq? ;
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:< lt? ;
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:> gt? ;
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:<= lteq? ;
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:>= gteq? ;
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~~~
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## Loops
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~~~
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:BEGIN |repeat ; immediate
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:AGAIN |again ; immediate
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:FOR |[ ; immediate
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:NEXT |] |times<with-index> ; immediate
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:DO |[ |[ |[ ; immediate
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:LOOP |] |dip |] |dip |n:inc |dup-pair |gt? |] |while |drop-pair ; immediate
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:+LOOP |] |dip |] |dip |swap |push |+ |pop |swap |dup-pair |gt? |] |while |drop-pair ; immediate
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~~~
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## I/O
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~~~
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:KEY (-c) c:get ;
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:EMIT (c-) c:put ;
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:. (n-) n:put sp ;
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:TYPE (an-) &c:put times ;
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:SPACE (-) sp ;
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:SPACES (n-) &sp times ;
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~~~
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## Maths
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~~~
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:/MOD /mod ;
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:0< n:negative? ;
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:0= n:zero? ;
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:0> n:positive? ;
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:1+ n:inc ;
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:1- n:dec ;
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:MAX n:max ;
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:MIN n:min ;
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:MOD mod ;
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:NEGATE n:negate ;
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:AND and ;
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:OR or ;
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:XOR xor ;
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~~~
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## Stack
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~~~
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:DUP dup ;
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:DROP drop ;
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:SWAP swap ;
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:OVER over ;
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:TUCK tuck ;
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:ROT rot ;
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:-ROT rot rot ;
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{{
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:save-stack (...-a)
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here [ depth &, times ] dip ;
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:fetch-prior (a-n[a-1])
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dup fetch swap n:dec ;
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:restore-stack (a-...)
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here swap - here n:dec swap [ fetch-prior ] times drop ;
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---reveal---
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:PICK (...n-...m)
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&Heap [ [ save-stack ] dip
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over + fetch [ restore-stack ] dip ] v:preserve ;
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}}
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{{
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:save-values (...n-a)
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[ , ] times here ;
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:restore-values (a-...)
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here - here swap [ fetch-next swap ] times drop ;
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---reveal---
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:ROLL (...n-...m)
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&Heap [ save-values ] v:preserve swap [ restore-values ] dip ;
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}}
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~~~
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## Strings
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Traditional Forth systems use a variety of strings. I define words
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to translate RETRO strings into these.
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~~~
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:caddr/u (a-an) dup s:length ;
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:counted (a-a) here [ dup s:length , s, ] dip ;
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:unpack (a-a) fetch-next here [ [ fetch-next , ] times drop #0 , ] dip ;
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:COUNT (a-an) fetch-next ;
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~~~
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## Compiler
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~~~
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:IMMEDIATE immediate ;
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:STATE &Compiler ;
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:LITERAL compile:lit ; immediate
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~~~
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## Dictionary
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~~~
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:FIND (caddr-caddr,0|xt,1|xt,-1)
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dup unpack d:lookup dup
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n:zero? [ drop #0 ] if; nip
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[ d:xt fetch ]
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[ d:class fetch &class:macro eq? [ #1 ] [ #-1 ] choose ] bi ;
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~~~
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## Unsorted
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~~~
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:CHAR+ n:inc ;
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:CHARS ;
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:CELL+ n:inc ;
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:CELLS ;
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:BL ASCII:SPACE ;
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~~~
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## Unsupported
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ANS, FIG, and other models have many words that I don't use or
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can't support directly in RETRO without changing the design of
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my system. The lists below are not exhaustive, but should be
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helpful in identifying things that may make porting code more
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difficult.
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The following words are not supported due to design choices in RETRO.
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-------- -------- -------- -------- -------- --------
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# #> #S ' ( ."
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['] : >IN [CHAR] ABORT" CONSTANT
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CREATE EXIT POSTPONE S" SOURCE VARIABLE
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WORD
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-------- -------- -------- -------- -------- --------
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The following are not supported due to limitations of the VM.
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-------- -------- -------- -------- -------- --------
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U. U< UM* UM/MOD
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-------- -------- -------- -------- -------- --------
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The following I do not plan to implement.
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-------- -------- -------- -------- -------- --------
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<# >BODY ABORT BASE ENVIRONMENT?
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FM/MOD QUIT SM/REM [ ]
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-------- -------- -------- -------- -------- --------
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