-- An example demonstrating how to connect a Happy parser to an Alex lexer.

{

import Tokens_posn

}

%name calc

%tokentype { Token }

%token  let		{ Let _     }

	in		{ In  _     }

	int		{ Int _ $$  }

	var		{ Var _ $$  }

	'='		{ Sym _ '=' }

	'+'		{ Sym _ '+' }

	'-'		{ Sym _ '-' }

	'*'		{ Sym _ '*' }

	'/'		{ Sym _ '/' }

	'('		{ Sym _ '(' }

	')'		{ Sym _ ')' }

%%

Exp :: { Exp }

Exp : let var '=' Exp in Exp	{ LetE $2 $4 $6 }

    | Exp1			{ $1            }

Exp1 : Exp1 '+' Term		{ PlusE  $1 $3  }

     | Exp1 '-' Term		{ MinusE $1 $3  }

     | Term			{ $1            }

Term : Term '*' Factor		{ TimesE $1 $3  }

     | Term '/' Factor		{ DivE $1 $3    }

     | Factor			{ $1            }

Factor : '-' Atom		{ NegE $2	}

       | Atom			{ $1		}

Atom : int			{ IntE $1       }

       | var			{ VarE $1       }

       | '(' Exp ')'		{ $2            }

{

data Exp =

	LetE   String Exp Exp |

	PlusE  Exp Exp        |

	MinusE Exp Exp        |

	TimesE Exp Exp        |

	DivE   Exp Exp        |

	NegE   Exp	      |

	IntE   Int            |

	VarE   String

	deriving Show

main:: IO ()

main = interact (show.runCalc)

runCalc :: String -> Exp

runCalc = calc . alexScanTokens

happyError :: [Token] -> a

happyError tks = error ("Parse error at " ++ lcn ++ "\n")

	where

	lcn = 	case tks of

		  [] -> "end of file"

		  tk:_ -> "line " ++ show l ++ ", column " ++ show c

			where

			AlexPn _ l c = token_posn tk

}