UNIX — универсальная среда программирования - Керниган Брайан Уилсон

 ;

cond: '(' expr ')' { code(STOP); $$ = $2; }

 ;

while: WHILE { $$ = code3(whilecode, STOP, STOP); }

 ;

if: IF { $$=code(ifcode); code3(STOP, STOP, STOP); }

 ;

end: /* nothing */ { code(STOP); $$ = progp; }

 ;

stmtlist: /* nothing */ { $$ = progp; }

 | stmtlist 'n'

 | stmtlist stmt

 ;

expr: NUMBER { $$ = code2(constpush, (Inst)$1); }

 | VAR { $$ = code3(varpush, (Inst)$1, eval); }

 | asgn

 | BLTIN '(' expr ')'

  { $$ = $3; code2(bltin,(Inst)$1->u.ptr); }

 | '(' expr ')' { $$ = $2; }

 | expr '+' expr { code(add); }

 | expr '-' expr { code(sub); }

 | expr '*' expr { code(mul); }

 | expr '/' expr { code(div); }

 | expr '^' expr { code (power); }

 | '-' expr %prec UNARYMINUS { $$ = $2; code(negate); }

 | expr GT expr { code(gt); }

 | expr GE expr { code(ge); }

 | expr LT expr { code(lt); }

 | expr LE expr { code(le); }

 | expr EQ expr { code(eq); }

 | expr NE expr { code(ne); }

 | expr AND expr { code(and); }

 | expr OR expr { code(or); }

 | NOT expr { $$ = $2; code(not); }

 ;

%%

/* end of grammar */

#include <stdio.h>

#include <ctype.h>

char *progname;

int lineno = 1;

#include <signal.h>

#include <setjmp.h>

jmp_buf begin;

int defining;

int c; /* global for use by warning() */

yylex() /* hoc5 */

{

 while ((c=getchar()) == ' ' || c == '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 = '';

  if ((s=lookup(sbuf)) == 0)

   s = install(sbuf, UNDEF, 0.0);

  yylval.sym = s;

  return s->type == UNDEF ? VAR : s->type;

 }

 switch (c) {

 case '>': return follow('=', GE, GT);

 case '<': return follow('=', LE, LT);

 case '=': return follow('=', EQ, '=');

 case '!': return follow('=', NE, NOT);

 case '|': return follow('|', OR, '|');

 case '&': return follow('&', AND, '&');

 case 'n': lineno++; return 'n';

 default: return c;

 }

}

follow(expect, ifyes, ifno) /* look ahead for >=, etc. */

{

 int c = getchar();

 if (c == expect)

  return ifyes;

 ungetc(c, stdin);

 return ifno;

}

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);

}

main(argc, argv)

 char *argv[];

{