forth/README.md

Forth
=====

This is a new implementation of Forth 2012 in C. 

Building & use
--------------

Use cmake or `build.sh`. It probably needs GCC with `--std=gnu99`.

You get a binary with the forth runtime. Run it to get a prompt. Use `-h` for help.

Goals
-----

- Comfy to use and extend
- No dynamic allocation where possible
- Compact and embeddable so it can be ported to ARM-CortexM or similar later
- Implement the CORE and CORE-EXT word sets, for a start
- Pass the [Forth2012 test suite](https://github.com/gerryjackson/forth2012-test-suite), at least for the word sets that are implemented
- Maybe eventually have some terminal-based implementation of (a subset of) the Facility word set, like AT-XY and keyboard input
- Try to keep added custom words and quirks at a minimum
- Comment stuff, maybe

Non-Goals
---------

- I don't really care about implementing some of the word sets
- Performance is not so critical for a hobby Forth like this
- Probably won't accept merge requests, this is my Forth
- I also don't care about someone telling me to add a license file

Custom words
------------
- `.\"` - like `."` but allows escaping, this is essentially `S\" blah" TYPE`, but without allocation (unless compiled)
- `??` - debug dump of the stacks
- `reset` - everything should become like if you restarted the program
- `debug ( flag -- )` - enable or disable verbose logging

For debug, there is `see ( "word" -- )` that lets you inspect and disassemble dictionary entries.

Implementation status
---------------------

*(this section may be outdated)*

Implemented (some may be wrong, like `FM/MOD`):

```
CORE:
! ' ( * */ */MOD + +! +LOOP , - . ." / /mod 0< 0= 1+ 1- 2! 2* 2/ 2@ 2DROP 2DUP 2OVER 2SWAP
: ; < = > >IN >R ?DUP @ ABORT ABS ALIGN ALIGNED ALLOT AND BASE BEGIN BL C! C, C@ CELL CELL+ CELLS CHAR CHAR+
CHARS CONSTANT COUNT CR CREATE DECIMAL DEPTH DO DOES> DROP DUP ELSE EMIT ENVIRONMENT? EXECUTE EXIT FM/MOD FIND
HERE I IF IMMEDIATE INVERT J LEAVE LITERAL LOOP LSHIFT M* MAX MIN MOD NEGATE OR OVER POSTPONE QUIT R> R@ RECURSE
REPEAT ROT RSHIFT S>D S" SM/REM SOURCE SPACE STATE SWAP THEN TYPE U< UNTIL UM* UM/MOD UNLOOP VARIABLE WHILE WORD XOR [ ['] [CHAR] ] 

CORE-EXT:
.( :NONAME 0<> 0> 2>R 2R> 2R@ <> ?DO AGAIN FALSE HEX NIP PAD PICK ROLL S\" TO TRUE TUCK U.R U> UNUSED VALUE
\

Other sets:
FORGET SEE BYE
```

Missing:

basically, CASE-OF, pictured numbers, keyboard input, some weirder metaprogramming things, manipulating the input buffer.

```
CORE:
# #> #S <# >BODY >NUMBER ABORT" ACCEPT EVALUATE FILL HOLD KEY MOVE SIGN SPACES U.

CORE-EXT:
.R ACTION-OF BUFFER: C" CASE COMPILE, DEFER DEFER! DEFER@ ENDCASE ENDOF ERASE HOLDS IS
MARKER OF PARSE PARSE-NAME REFILL RESTORE-INPUT SAVE-INPUT SOURCE-ID WITHIN [COMPILE]
```

.