parser.ypp

Lexx Bison programm Lexx Bison Lexx Bison

%{
  /*
    bison spec
   */
#include <stdio.h>
#include <iostream>
#include <string>
#include <map>
  double variableTable[26];

class symbol
{
	std::string id;
	double value;
	double (*action)(double);
};

std::map<std::string, symbol> symbolTable;

int yyerror(char *s);
extern int yylex();
extern int yyget_lineno();
%}

%union {
  double doubleValue;
  int variableNumber;
}

%token IF ELSE ELSEIF ENDIF opSet opEqual 
%token WHILE ENDWHILE 
%token <variableNumber> ID 
%token <doubleValue> NUMBER

%left "=="
%left '+' '-'
%left '*' '/'

%type <doubleValue> expr

%%

program : program block | /* empty */  { printf("program:\n"); }
block : instructions | if_block | while_block;
if_block: IF '(' expr ')' block else_block ENDIF  { printf("if\n"); }
else_block: /*empty*/ | ELSE block | ELSEIF '(' expr ')' block;
while_block: WHILE '(' expr ')' block ENDWHILE  { printf("while\n"); }

expr : ID { $$ = variableTable[$1]; printf("variable\n"); }
| NUMBER { $$ = $1; }
| expr '+' expr { $$ = $1 + $3; }
| expr '-' expr { $$ = $1 - $3; }
| expr '*' expr { $$ = $1 * $3; }
| expr '/' expr { 
if ($3 == 0) 
  yyerror("divide by zero");
 else 
   $$ = $1 / $3; 
}
| expr opEqual expr { $$ = ($1 == $3); printf("equal\n"); }

instructions: instruction | instructions instruction;
instruction: ID opSet expr ';'  { variableTable[$1]=$3; }

%%
      /* skip */

int yyerror(char *s) 
{
  printf("error: %s, line %d\n",s, yyget_lineno());
}