49 lines
1.1 KiB
Haskell
49 lines
1.1 KiB
Haskell
-- see https://markkarpov.com/tutorial/megaparsec.html
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{-# LANGUAGE ImportQualifiedPost #-}
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module Parser.Expr (parseExpr, ParseResult) where
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import Control.Monad.Combinators.Expr
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import Data.Functor.Identity qualified
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import Data.Void (Void)
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import Text.Megaparsec as MP
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import Text.Megaparsec.Char as C
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import Text.Megaparsec.Char.Lexer as L
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import Types.Expr
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type Parser = Parsec Void String
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lexemeParser :: Parser a -> Parser a
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lexemeParser = L.lexeme C.space
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symbolParser :: String -> Parser String
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symbolParser = L.symbol C.space
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intParser :: Parser Int
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intParser = lexemeParser L.decimal
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term :: Parser Expr
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term = Lit <$> intParser
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table :: [[Operator Parser Expr]]
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table =
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[ [ binaryOp "*" Mul
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-- binaryOp "/" Div
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],
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[ binaryOp "+" Add,
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binaryOp "-" Sub
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]
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]
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binaryOp :: String -> (a -> a -> a) -> Operator (ParsecT Void String Data.Functor.Identity.Identity) a
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binaryOp name f = InfixL (f <$ symbolParser name)
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expr :: Parser Expr
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expr = makeExprParser term table
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type ParseResult = Either (ParseErrorBundle String Void) Expr
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parseExpr :: String -> ParseResult
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parseExpr = MP.parse (C.space *> expr <* eof) ""
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-- parseE = parseExpr |