{
module Main where
import Char
}


%name myparser
%tokentype { Token }

%token 
       '+'             { TokenPlus }
       '*'             { TokenTimes }
       'a'             { TokenA }
       '('             { TokenOB }
       ')'             { TokenCB }
       
%left '+'
%left '*'       
       
%%

Exp   : Exp  '+' Exp           { Plus $1 $3 }
      | Exp  '*' Exp           { Times $1 $3 }
      | '(' Exp ')'            { Brack $2 }    
      | 'a'                    { Id }



{


happyError :: [Token] -> a
happyError inp = error ("Parse error " ++ concatMap show inp)

       
data Exp  
       = Plus Exp  Exp 
       | Times Exp Exp
       | Brack Exp
       | Id       
       deriving Show


data Token
       = TokenA 
       | TokenPlus
       | TokenTimes
       | TokenOB
       | TokenCB
       deriving Show
  
lexer :: String -> [Token]
lexer [] = []
lexer (c:cs) 
       | isSpace c = lexer cs
lexer ('a':cs) = TokenA : lexer cs
lexer ('+':cs) = TokenPlus : lexer cs
lexer ('*':cs) = TokenTimes : lexer cs
lexer ('(':cs) = TokenOB : lexer cs
lexer (')':cs) = TokenCB : lexer cs



test = myparser . lexer
}