language start pieces

lang.l

%option noyywrap yylineno

%{
#include "lang.tab.h"
%}

DIGIT ([0-9])
LETTER ([a-zA-Z])

%%
"-" |
"(" |
"," |
"=" |
")" { return yytext[0]; }
"if"        { return IF; }
"then"      { return THEN; }
"else"      { return ELSE; }
"let"       { return LET;}
"in"        { return IN;}
"zero?"     { return ZERO;}
{LETTER}({DIGIT}|{LETTER}|"_"|"-"|"?")*  { yylval.str = yytext; return VAR; }

[+-]?{DIGIT}{DIGIT}* { yylval.i = atoi(yytext); return NUMBER; }

"%".*   /*ignored*/
[ \t\r\n]   /*ignored*/
%%

lang.y

%{
#include <stdio.h>
#include "let.h"
%}
%union {
struct ast *a;
struct boolexp *b;
char *str;
int i;
}

%token <i> NUMBER
%token <str> VAR
%token IF THEN ELSE LET IN ZERO
%token EOL

%type <a> exp
%type <b> boolexp 

%%

prog:   stmt prog
    |   
    ;

stmt:   exp     { 
        struct ast *a = $1;
        printf("exp = %d\n", eval(a));
        freeAll(a);
    }
    ;

exp:    NUMBER  { $$ = new_num($1); }
   |    VAR     { printf("var %s\n", $1); $$=0; }
   |    '-' '(' exp ',' exp ')' {
        $$ = new_diff_exp($3, $5);
   }
   |    IF boolexp THEN exp ELSE exp {
        $$ = new_if_exp($2, $4, $6);
   }
   |    LET VAR '=' exp IN exp {
        printf("let var = exp in exp\n");
   }
   ;

boolexp:    ZERO '(' exp ')' { $$ = new_boolexp($3); }
       ;

%%