UNIX — универсальная среда программирования - Керниган Брайан Уилсон

 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();

3.4.2 hoc.y

%{

#include "hoc.h"

extern double Pow();

%}

%union {

 double val; /* actual value */

 Symbol *sym; /* symbol table pointer */

}

%token <val> NUMBER

%token <sym> VAR BLTIN UNDEF

%type <val> expr asgn

%right '='

%left '+' '-'

%left '*' '/'

%left UNARYMINUS

%right '^' /* exponentiation */

%%

list: /* nothing */

 | list 'n'

 | list asgn 'n'

 | list expr 'n' { printf("t%.8gn", $2); }

 | list error 'n' { yyerrok; }

 ;

asgn: VAR '=' expr { $$=$1->u.val=$3; $1->type = VAR; }

 ;

expr: NUMBER

 | VAR {

  if ($1->type == UNDEF)

   execerror("undefined variable", $1->name);

  $$ = $1->u.val;

 }

 | asgn

 | BLTIN '(' expr ')' { $$ = (*($1->u.ptr))($3); }

 | expr '+' expr { $$ = $1 + $3; }

 | expr '+' expr { $$ = $1 - $3; }

 | expr '*' expr { $$ = $1 * $3; }

 | expr '/' expr {

  if ($3 == 0.0)

   execerror("division by zero", "");

  $$ = $1 / $3;

 }

 | expr '^' expr { $$ = Pow($1, $3); }

 | '(' expr ')' { $$ = $2; }

 | '-' expr %prec UNARYMINUS { $$ = -$2; }

 ;

%%

/* end of grammar */

#include <stdio.h>

#include <ctype.h>

char *progname;

int lineno = 1;

#include <setjmp.h>

jmp_buf begin;

main(argc, argv) /* hoc3 */

 char *argv[];

{

 progname = argv[0];

 init();

 setjmp(begin);

 yyparse();

}

yyerror(s)

 char *s;

{

 warning(s, (char *)0);

}

execerror(s, t)

 char *s, *t;

{

 warning(s, t);

 longjmp(begin, 0);

}

warning(s, t)

 char *s, *t;

{

 fprintf (stderr, "%s: %s", progname, s);

 if (t && *t)

  fprintf(stderr, " %s", t);

 fprintf(stderr, " near line %dn", lineno);

}

3.4.3 init.c

#include "hoc.h"

#include "y.tab.h"

#include <math.h>

extern double Log(), Log10(), Exp(), Sqrt(), integer();

static struct { /* Constants */

 char *name;

 double eval;

} consts [] = {

 "PI",    3.14159265358979323846,

 "E",     2.71828182845904523536,

 "GAMMA", 0.57721566490153286060, /* Euler */

 "DEG",  57.29577951308232087680, /* deg/radian */

 "PHI",   1.61803398874989484820, /* golden ratio */

 0,       0

};

static struct { /* Built-ins */

 char *name;