DWC is an extremely minimal single-file Forth system that can run stand-alone or be embedded into another program.
DWC is implemented in a single file, 275 lines, 32 primitives.
On Windows, a 32-bit Release build compiles to a 16k executable.
On a Linux box, it is about 24k.
DWC stands for "dword-code". This is inspired by Tachyon.
In a DWC program, each instruction is a DWORD.
- If <= the last primitive (31), then it is a primitive.
- Else, if <= NUM_BITS ($3FFFFFFF), then it is a literal.
- Else, it is the XT (code address) of a word in the dictionary.
DWC supports control chars in the whitespace to change the state.
DWC has 4 states: COMPILE, DEFINE, INTERPRET, and COMMENT.
This gives the operator more flexibility.
| Ascii | State |
|---|---|
| 1 | COMPILE |
| 2 | DEFINE |
| 3 | INTERPRET |
| 4 | COMMENT |
| Word | Action |
|---|---|
| : | Change state to DEFINE. |
| ; | Compile EXIT and change state to INTERPRET. |
| [ | Change state to INTERPRET. |
| ] | Change state to COMPILE. |
| ( | Change state to COMMENT. |
| ) | Change state to COMPILE. |
| (( | Change state to COMMENT. |
| )) | Change state to INTERPRET. |
| State | Behavior |
|---|---|
| COMPILE | Compile the current word/number. |
| DEFINE | Add the current word to the dictionary, change to COMPILE. |
| INTERPRET | Execute the current word. |
| COMMENT | Ignore the current word if it is not ')' or '))'. |
NOTE: When in the COMMENT state, only ')' or '))' changes the state.
| Primitive | Word | Action |
|---|---|---|
| 0 | exit | PC = RTOS. Discard RTOS. If (PC=0) then stop. |
| 1 | (lit) | Push code[PC]. Increment PC. |
| 2 | (jmp) | PC = code[PC]. |
| 3 | (jmpz) | If (TOS=0) then PC = code[PC] else PC = PC+1. Discard TOS. |
| 4 | (jmpnz) | If (TOS!=0) then PC = code[PC] else PC = PC+1. Discard TOS. |
| 5 | 1+ | Increment TOS. |
| 6 | dup | Push TOS. |
| 7 | drop | Discard TOS. |
| 8 | swap | Swap TOS and NOS. |
| 9 | ! | CELL store NOS through TOS. Discard TOS and NOS. |
| 10 | @ | CELL fetch TOS through TOS. |
| 11 | c! | BYTE store NOS through TOS. Discard TOS and NOS. |
| 12 | c@ | BYTE fetch TOS through TOS. |
| 13 | >r | Push TOS onto the return stack. Discard TOS. |
| 14 | r@ | Push RTOS. |
| 15 | r> | Push RTOS. Discard RTOS. |
| 16 | timer | Push clock(). |
| 17 | * | TOS = NOS*TOS. Discard NOS. |
| 18 | + | TOS = NOS+TOS. Discard NOS. |
| 19 | - | TOS = NOS-TOS. Discard NOS. |
| 20 | /mod | TOS = NOS/TOS. NOS = NOS%TOS. |
| 21 | < | If (NOS<TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 22 | = | If (NOS=TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 23 | > | If (NOS<TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 24 | emit | Output char TOS to STDOUT. Discard TOS. |
| 25 | ztype | Output null-terminated string TOS to STDOUT. Discard TOS. |
| 26 | add-word | Add the next word to the dictionary. |
| 27 | for | Start a FOR loop. |
| 28 | next | End the current FOR loop. |
| 29 | and | TOS = NOS and TOS. Discard NOS. |
| 30 | or | TOS = NOS or TOS. Discard NOS. |
| 31 | xor | TOS = NOS xor TOS. Discard NOS. |
- Include dwc.c in your project.
- Rename the main() to dwc_init().
- Tweak the renamed function to suit your needs.
- Add additional primitives to PRIMS macro to suit your needs.
- Call dwc_init() to initialize the VM.
- Pass Forth code to outer().
- The stack is dstk[].
- The stack pointer is dsp. Set it to 0 to clear the stack.
- The top of the stack is dstk[dsp].