Книга: UNIX — универсальная среда программирования

3.2.1 hoc.y

3.2.1 hoc.y
%{
double mem[26]; /* memory for variables 'a'..'z' */
%}
%union { /* stack type */
 double val; /* actual value */
 int index; /* index into mem[] */
}
%token <val> NUMBER
%token <index> VAR
%type <val> expr
%right '='
%left '+' '-'
%left '*' '/'
%left UNARYMINUS
%%
list: /* nothing */
 | list 'n'
 | list expr 'n' { printf("t%.8gn $2); }
 | list error 'n' { yyerrok; }
 ;
expr: NUMBER
 | VAR { $$ = mem[$1]; }
 | VAR '=' expr { $$ = mem[$1] = $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 ')' { $$ = $2; }
 | '-' expr %prec UNARYMINUS { $$ = -$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) /* hoc2 */
 char *argv[];
{
 int fpecatch();
 progname = argv[0];
 setjmp(begin);
 signal(SIGFPE, fpecatch);
 yyparse();
}
yylex() /* hoc2 */
{
 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 (islower(c)) {
  yylval.index = c - 'a'; /* ASCII only */
  return VAR;
 }
 if (c == 'n')
  lineno++;
 return c;
}
yyerror(s) /* report compile-time error */
 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) /* print warning message */
 char *s, *t;
{
 fprintf(stderr. "%s: %s", progname, s);
 if (t && *t)
  fprintf(stderr, " %s , t);
 fprintf(stderr, " near line %dn", lineno);
}

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