UNIX — универсальная среда программирования

3.4.1. 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;

3.4.2 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%.8g\n", $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 %d\n", 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;
  double (*func);
 } builtins[] = {
  "sin", sin,
  "cos", cos,
  "atan", atan,
  "log", Log, /* checks argument */
  "log10", Log10, /* checks argument */
  "exp", Exp, /* checks argument */
  "sqrt", Sqrt, /* checks argument */
  "int", integer,
  "abs", fabs,
  0, 0
 };

 init /* install constants and built-ins in table */
 {
  int i;
  Symbol *s;

  for (i = 0; consts[i].name; i++)
  install(consts[i].name, VAR, consts[i].eval);