UNIX — универсальная среда программирования

  } 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[];
 extern eval, add, sub, mul, div, negate, power;
 extern assign, bltin, varpush, constpush, print;

3.5.3 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 VAR BLTIN UNDEF
 %right '='
 %left '+' '-'
 %left '*' '/'
 %left UNARYMINUS
 %right '^' /* exponentiation */
 %%
 list: /* nothing */
  | list '\n'
  | list asgn '\n' { code2(pop, STOP); return 1; }
  | list expr '\n' { code2(print, STOP); return 1; }
  | list error '\n' { yyerrok; }
  ;
 asgn: VAR '=' expr { code3(varpush,(Inst)$1.assign); }
  ;
 expr: NUMBER { code2(constpush, (Inst)$1); }
  | VAR { code3(varpush, (Inst)$1, eval); }
  | asgn
  | BLTIN '(' expr ')' { code2(bltin, (Inst)$1->u.ptr); }
  | '(' expr ')'
  | expr '+' expr { code(add); }
  | expr '-' expr { code(sub); }
  | expr '*' expr { code(mul); }
  | expr '/' expr { code(div); }
  | expr '^' expr { code(power); }
  | '-' expr %prec UNARYMINUS { code(negate); }
  ;
 %%
 /* end of grammar */
 #include <stdio.h>
 #include <ctype.h>
 char *progname;
 int lineno = 1;
 #include <signal.h>
 #include <setjmp.h>
 jmp_buf begin;

 main(argc, argv) /* hoc4 */
  char *argv[];
 {
  int fpecatch;
  progname = argv[0];
  init;
  setjmp(begin);
  signal(SIGFPE, fpecatch);
  for (initcode; yyparse; initcode)
  execute(prog);
  return 0;
 }

 static int c; /* global for use by warning */

 yylex /* hoc4 */
 {
while ((c=getchar) == ' ' || с == '\t')
  ;
  if (c == EOF)
  return 0;
  if (c == '.' || isdigit(c)) { /* number */
  double d;
  ungetc(c, stdin);
  scanf ("%lf", &d);
  yylval.sym = install("", NUMBER, d);
  return NUMBER;
  }
  if (isalpha(c)) {
  Symbol *s;
  char sbuf[100], *p = sbuf;
  do {
  *p++ = c;
  } while ((c=getchar) != EOF && isalnum(c));
  ungetc(c, stdin);
  *p = '\0';
  if ((s=lookup(sbuf)) == 0)
  s = install(sbuf, UNDEF, 0.0);
  yylval.sym = s;
  return s->type == UNDEF ? VAR : s->type;
  }
  if (c == '\n')
  lineno++;
  return c;
 }

 yyerror(s)
  char *s;
 {
  warning(s, (char *)0);
 }

 execerror(s, t) /* recover from run-time error */
  char *s, *t;
 {
  warning(s, t);
  longjmp(begin, 0);
 }

 fpecatch /* catch floating point exceptions */
 {
  execerror("floating point exception", (char*)0);
 }

 warning(s, t)
  char *s, *t;
 {
  fprintf(stderr, "%s: %s", progname, s);
  if (t && *t)
  fprintf(stderr, " %s", t);
  fprintf(stderr, " near line %d\n", lineno);
  while (c != '\n' && с != EOF)