38 lines
1.1 KiB
Haskell
38 lines
1.1 KiB
Haskell
module LambdaCalculus.Parser (parseExpression) where
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import Control.Applicative ((*>))
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import Control.Monad (void)
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import LambdaCalculus.Expression (Expression (Variable, Application, Abstraction))
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import Text.Parsec hiding (spaces)
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import Text.Parsec.String
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spaces :: Parser ()
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spaces = void $ many1 space
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variableName :: Parser String
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variableName = many1 letter
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variable :: Parser Expression
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variable = Variable <$> variableName
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application :: Parser Expression
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application = foldl1 Application <$> sepBy1 applicationTerm spaces
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where applicationTerm :: Parser Expression
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applicationTerm = variable <|> abstraction <|> grouping
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where grouping :: Parser Expression
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grouping = between (char '(') (char ')') expression
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abstraction :: Parser Expression
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abstraction = do
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char '^'
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names <- sepBy1 variableName spaces
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char '.'
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body <- expression
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pure $ foldr Abstraction body names
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expression :: Parser Expression
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expression = abstraction <|> application <|> variable
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parseExpression :: String -> Either ParseError Expression
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parseExpression = parse (expression <* eof) "input"
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