UNIX — универсальная среда программирования

 clean:
  rm -f $(OBJS) y.tab.[ch]

3.3.2 hoc.h

 typedef struct Symbol { /* symbol table entry */
  char *name;
  short type; /* VAR, BLTIN, UNDEF */
  union {
  double val; /* if VAR */
  double (*ptr); /* if BLTIN */
  } u;
  struct Symbol *next; /* to link to another */
 } Symbol;
 Symbol *install, *lookup;

3.3.3 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%.8g\n", $2); }
  | list error '\n' { yyerrok; }
  ;
 asgn: VAR '=' expr { $$=$1->u.val=$3; $1->type = VAR; }
  ;
 expr: NUMBER
  | VAR { if ($l->type == UNDEF)
  execerror("undefined variable", $1->name);
  $$ = $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 <signal.h>
 #include <setjmp.h>

 jmp_buf begin;

 main(argc, argv) /* hoc3 */
  char *argv[];
 {
  int fpecatch;
  progname = argv[0];
  init;
  setjmp(begin);
  signal(SIGFPE, fpecatch);
  yyparse;
 }

 yylex /* hoc3 */
 {
  int c;

  while ((c=getchar) == ' ' || c == '\t')
  ;
  if (c == EOF)
  return 0;
  if (c == '.' || isdigit(c)) {
  /* number */
  ungetc(c, stdin);
  scanf("%lf", &yylval.val);
  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);
 }

3.3.4 init.c

 #include "hoc.h"
 #include "y.tab.h"