}
Inst *code(f) /* install one instruction or operand */
Inst f;
{
Inst *oprogp = progp;
if (progp >= &prog[NPROG])
execerror("expression too complicated", (char*)0);
*progp++ = f;
return oprogp;
}
execute(p)
Inst *p;
{
for (pc = p; *pc != STOP; ) (*(*pc++))();
}
3.6.2
fib
{
a=0
b=1
while(b<1000) {
c=b
b=a+b
a=c
print(c)
}
}
3.6.3
fib2
{
n=0
a=0
b=1
while(b<10000000){
n=n+1
c=b
b=a+b
a=c
print(b)
}
print(n)
}
3.6.4
hoc.h
typedef struct Symbol { /* symbol table entry */
char *name;
short type; /* VAR, BLTIN, UNDEF */
union {
double val; /* if VAR */
double (*ptr)(); /* if BLTIN */
} u;
struct Symbol *next; /* to link to another */
} Symbol;
Symbol *install(), *lookup();
typedef union Datum { /* interpreter stack type */
double val;
Symbol *sym;
} Datum;
extern Datum pop();
typedef int (*Inst)(); /* machine instruction */
#define STOP (Inst)0
extern Inst prog[], *progp, *code();
extern eval(), add(), sub(), mul(), div(), negate(), power();
extern assign(), bltin(), varpush(), constpush(), print();
extern prexpr();
extern gt(), lt(), eq(), ge(), le(), ne(), and(), or(), not();
extern ifcode(), whilecode();
3.6.5
hoc.y
%{
#include "hoc.h"
#define code2(c1,c2) code(c1); code(c2)
#define code3(c1,c2,c3) code(c1); code(c2); code(c3)
%}
%union {
Symbol *sym; /* symbol table pointer */
Inst *inst; /* machine instruction */
}
%token <sym> NUMBER PRINT VAR BLTIN UNDEF WHILE IF ELSE
%type <inst> stmt asgn expr stmtlist cond while if end
%right '='
%left OR
%left AND
%left GT GE LT LE EQ NE
%left '+' '-'
%left '*' '/'
%left UNARYMINUS NOT
%right
%%
list: /* nothing */
| list '\n'
| list asgn '\n' { code2(pop, STOP); return 1; }
| list stmt '\n' { code(STOP); return 1; }
| list expr '\n' { code2(print, STOP); return 1; }
| list error '\n' { yyerrok; }
;
asgn: VAR '=' expr { $$=$3; code3(varpush,(Inst)$1.assign); }
;
stmt: expr { code(pop); }
| PRINT expr { code(prexpr); $$ = $2; }
| while cond stmt end {
($1)[1] = (Inst)$3; /* body of loop */
($1)[2] = (Inst)$4;
} /* end, if cond fails */
| if cond stmt end { /* else-less if */
($1)[1] = (Inst)$3; /* thenpart */
($1)[2] = (Inst)$4;
} /* end, if cond fails */
| if cond stmt end ELSE stmt end { /* if with else */
($1)[1] = (Inst)$3; /* thenpart */
($1)[2] = (Inst)$6; /* elsepart */
($1)[3] = (Inst)$7;
} /* end, if cond fails */
| '{' stmtlist '}' { $$ = $2; }
