[分享] zForth
https://github.com/zevv/zForth
zForth: tiny, embeddable, flexible, compact Forth scripting language
for embedded systems
之前想找一個易於修改的 VM 做為我的遊戲核心，發現這套系統易於了解和修改。
特別的地方是內建 bytecode 的 trace 功能。
: square dup * ;
: test 5 square . ;
test
test
r>0
[test/0326]
0326 0001 ｜ (lit) >5
0328 031c ｜ square/031c r>810
031c 000b ｜ ｜ (dup) <5 >5 >5
031d 0007 ｜ ｜ (*) <5 <5 >25
031e 0000 ｜ ｜ (exit) r<810
032a 0133 ｜ ./0133 r>812
0133 0001 ｜ ｜ (lit) >1
0135 0019 ｜ ｜ (sys) <1 <25
0136 0000 ｜ ｜ (exit) r<812
032c 0000 ｜ (exit) r<0 25
https://github.com/zevv/zForth/blob/master/src/zforth/zforth.c
Forth 的 compiler 實作很簡單，查表再執行即可。
定義函式用 ":" 開頭 ";" 結束。
":" (PRIM_COL) "main" "1" "2" "3" "+" "+" ";" (PRIM_SEMICOL)
/*
* Find word in dictionary, returning address and execution token
*/
static int find_word(const char *name, zf_addr *word, zf_addr *code)
{
zf_addr w = LATEST;
size_t namelen = strlen(name);
while(w) {
zf_cell link, d;
zf_addr p = w;
size_t len;
p += dict_get_cell(p, &d);
p += dict_get_cell(p, &link);
len = ZF_FLAG_LEN((int)d);
if(len == namelen) {
const char *name2 = (const char *)&dict[p];
if(memcmp(name, name2, len) == 0) {
*word = w;
*code = p + len;
return 1;
}
}
w = link;
}
return 0;
}
static void do_prim(zf_prim op, const char *input)
{
zf_cell d1, d2, d3;
zf_addr addr, len;
trace("(%s) ", op_name(op));
switch(op) {
case PRIM_COL:
if(input == NULL) {
input_state = ZF_INPUT_PASS_WORD;
} else {
create(input, 0);
COMPILING = 1;
}
break;
case PRIM_LTZ:
zf_push(zf_pop() < 0);
break;
case PRIM_SEMICOL:
dict_add_op(PRIM_EXIT);
trace("\n===");
COMPILING = 0;
break;
...
/*
* Create new word, adjusting HERE and LATEST accordingly
*/
static void create(const char *name, int flags)
{
zf_addr here_prev;
trace("\n=== create '%s'", name);
here_prev = HERE;
dict_add_cell((strlen(name)) | flags);
dict_add_cell(LATEST);
dict_add_str(name);
LATEST = here_prev;
trace("\n===");
}
--
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