UNIX — универсальная среда программирования

 #define NPROG 2000
 Inst prog[NPROG]; /* the machine */
 Inst *progp; /* next free spot for code generation */
 Inst *pc; /* program counter during execution */

 initcode /* initialize for code generation */
 {
  stackp = stack;
  progp = prog;
 }

 push(d) /* push d onto stack */
  Datum d;
 {
  if (stackp >= &stack[NSTACK])
  execerror("stack overflow", (char*)0);
  *stackp++ = d;
 }

 Datum pop /* pop and return top elem from stack */
 {
  if (stackp <= stack)
  execerror("stack underflow", (char*)0);
  return *--stackp;
 }

 constpush /* push constant onto stack */
 {
  Datum d;
  d.val = ((Symbol*)*pc++)->u.val;
  push(d);
 }

 varpush /* push variable onto stack */
 {
  Datum d;
  d.sym = (Symbol*)(*pc++);
  push(d);
 }

 bltin /* evaluate built-in on top of stack */
 {
  Datum d;
  d = pop;
  d.val = (*(double(*))(*pc++))(d.val);
  push(d);
 }

 eval /* evaluate variable on stack */
 {
  Datum d;
  d = pop ;
  if (d.sym->type == UNDEF)
  execerror("undefined variable", d.sym->name);
  d.val = d.sym->u.val;
  push(d);
 }

 add /* add top two elems on stack */
 {
  Datum d1, d2;
  d2 = pop;
  d1 = pop;
  d1.val += d2.val;
  push(d1);
 }

 sub /* subtract top of stack from next */
 {
  Datum d1, d2;
  d2 = pop;
  d1 = pop;
  d1.val -= d2.val;
  push(d1);
 }

 mul {
  Datum d1, d2;
  d2 = pop;
  d1 = pop;
  d1.val *= d2.val;
  push(d1);
 }

 div {
  Datum d1, d2;
  d2 = pop;
  if (d2.val == 0.0)
  execerror("division by zero", (char*)0);
  d1 = pop;
  d1.val /= d2.val;
  push(d1);
 }

 negate {
  Datum d;
  d = pop;
  d.val = -d.val;
  push(d);
 }

 power {
  Datum d1, d2;
  extern double Pow;
  d2 = pop;
  d1 = pop;
  d1.val = Pow(d1.val, d2.val);
  push(d1);
 }

 assign /* assign top value to next value */
 {
  Datum d1, d2;
  d1= pop;
  d2 = pop;
  if (d1.sym->type != VAR && d1.sym->type != UNDEF)
  execerror("assignment to non-variable", d1.sym->name);
  d1.sym->u.val = d2.val;
  d1.sym->type = VAR;
  push(d2);
 }

 print /* pop top value from stack, print it */
 {
  Datum d;
  d = pop;
  printf("\t%8g\n", d.val);
 }

 Inst *code(f) /* install one instruction or operand */
  Inst f;
 {
  Inst *oprogp = progp;
  if (progp >= &eprog[NPROG])
  execerror("program too big", (char*)0);
  *progp++ = f;
  return oprogp;
 }

 execute(p) /* run the machine */
  Inst *p;
 {
  for (pc = p; *pc != STOP; )
  (*(*pc++));
 }

3.5.2 hoc.h

 typedef struct Symbol { /* symbol table entry */
  char *name;
  short type; /* VAR, BLTIN, UNDEF */
  union {
  double val; /* if VAR */
  double (*ptr); /* if BLTIN */