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Parser1.y
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Parser1.y
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{
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE PartialTypeSignatures #-}
module Language.Arith.Parser (
parseAexpr
, parseTokens
) where
import Language.Arith.Lexer
import Language.Arith.Types hiding (Arith (..))
import Control.Monad.Except
import Control.Exception
}
-- Entry point
%name aexpr
-- Lexer structure
%tokentype { Token }
-- Parser monad
%monad { Except String } { (>>=) } { return }
%error { parseError }
-- Token Names
%token
TNUM { NUM _ $$ }
ID { ID _ $$ }
'+' { PLUS _ }
'-' { MINUS _ }
'*' { MUL _ }
'/' { DIV _ }
'(' { LPAREN _ }
')' { RPAREN _ }
-- Operators
%left '+' '-'
%left '*' '/'
%%
Aexpr : BinExp { $1 }
| TNUM { AConst $1 }
| ID { AVar $1 }
| '(' Aexpr ')' { $2 }
BinExp : Aexpr '+' Aexpr { APlus $1 $3 }
| Aexpr '-' Aexpr { AMinus $1 $3 }
| Aexpr '*' Aexpr { AMul $1 $3 }
| Aexpr '/' Aexpr { ADiv $1 $3 }
{
parseError :: [Token] -> Except String a
parseError (l:ls) = throwError (show l)
parseError [] = throwError "Unexpected end of Input"
parseAexpr :: String -> Aexpr
parseAexpr s = case parseAexpr' s of
Left msg -> throw (Error ("parse error:" ++ msg))
Right e -> e
parseAexpr' input = runExcept $ do
tokenStream <- scanTokens input
aexpr tokenStream
parseTokens :: String -> Either String [Token]
parseTokens = runExcept . scanTokens
}