DWC is an extremely minimal Forth system that can run stand-alone or be embedded into another program.
DWC has 32 base primitives, 13 system primitives.
DWC is implemented in 3 files: (dwc-vm.c, dwc-vm.h, system.c).
The VM itself is 250 lines of code.
On Windows, a 32-bit Release build compiles to a 17k 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 (44), then it is a primitive.
- Else, if >= LIT_BITS ($3FFFFFFF), then it is a literal anded with LIT_BITS.
- 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.
An INLINE word is somewhat similar to a macro in other languages.
When a word is INLINE, its definition is copied to the target.
When not INLINE, a call is made to the word instead.
Words 't0' through 't9' are transient and are not added to the dictionary.
They help with factoring code and and keep the dictionary uncluttered.
They are case sensitive: 't0' is a transient word, 'T0' is not.
| Primitive | Word | Stack | Action |
|---|---|---|---|
| --- DWC primitives --- | |||
| 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 | (n--) | If (TOS==0) then PC = code[PC] else PC = PC+1. Discard TOS. |
| 4 | jmpnz | (n--) | If (TOS!=0) then PC = code[PC] else PC = PC+1. Discard TOS. |
| 5 | njmpz | (n--n) | If (TOS==0) then PC = code[PC] else PC = PC+1. |
| 6 | njmpnz | (n--n) | If (TOS!=0) then PC = code[PC] else PC = PC+1. |
| 7 | dup | (n--n n) | Push TOS. |
| 8 | drop | (n--) | Discard TOS. |
| 9 | swap | (a b--b a) | Swap TOS and NOS. |
| 10 | over | (a b--a b a) | Push NOS. |
| 11 | ! | (n a--) | CELL store NOS through TOS. Discard TOS and NOS. |
| 12 | @ | (a--n) | CELL fetch TOS through TOS. |
| 13 | c! | (b a--) | BYTE store NOS through TOS. Discard TOS and NOS. |
| 14 | c@ | (a--b) | BYTE fetch TOS through TOS. |
| 15 | >r | (n--) | Push TOS onto the return stack. Discard TOS. |
| 16 | r@ | (--n) | Push RTOS. |
| 17 | r> | (--n) | Push RTOS. Discard RTOS. |
| 18 | * | (a b--c) | TOS = NOS*TOS. Discard NOS. |
| 19 | + | (a b--c) | TOS = NOS+TOS. Discard NOS. |
| 20 | - | (a b--c) | TOS = NOS-TOS. Discard NOS. |
| 21 | /mod | (a b--r q) | TOS = NOS/TOS. NOS = NOS modulo TOS. |
| 22 | < | (a b--f) | If (NOS<TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 23 | = | (a b--f) | If (NOS=TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 24 | > | (a b--f) | If (NOS<TOS) then TOS = 1 else TOS = 0. Discard NOS. |
| 25 | +! | (n a--) | Add NOS to the cell at TOS. Discard TOS and NOS. |
| 26 | ' | (--a) | Push the address of the next word from the dictionary. |
| 27 | for | (n--) | Start a FOR loop. |
| 28 | next | (--) | End the current FOR loop. |
| 29 | and | (a b--c) | TOS = NOS and TOS. Discard NOS. |
| 30 | or | (a b--c) | TOS = NOS or TOS. Discard NOS. |
| 31 | xor | (a b--c) | TOS = NOS xor TOS. Discard NOS. |
| --- System primitives --- | |||
| 32 | key | (--n) | Push the next keypress. Wait until one is available. |
| 33 | ?key | (--n) | Push 1 if a keypress is available, else 0. |
| 34 | emit | (n--) | Output char TOS. Discard TOS. |
| 35 | ztype | (a--) | Output null-terminated string TOS. Discard TOS. |
| 36 | fopen | (nm md--h) | Open file NOS using mode TOS (h=0 if error). |
| 37 | fclose | (h--) | Close file TOS. Discard TOS. |
| 38 | fread | (a sz h--n) | Read NOS chars from file TOS to a. |
| 39 | fwrite | (a sz h--n) | Write NOS chars from file TOS from a. |
| 40 | ms | (n--) | Wait/sleep for TOS milliseconds |
| 41 | timer | (--n) | Push the current system time. |
| 42 | add-word | (--) | Add the next word to the dictionary. |
| 43 | outer | (a--) | Run the outer interpreter on TOS. Discard TOS. |
| 44 | system | (a--) | Execute system(TOS). Discard TOS. |
See system.c. It embeds the DWC VM into a C program.