Parse.hs

module Parse where

import Text.ParserCombinators.Parsec (ParseError, many1, many, letter, char, string, between, (<|>), digit)
import qualified Text.Parsec


type Identifier = String

data Expression = BooleanLiteral Bool
                | IntegerLiteral Integer
                | Abstraction Identifier TypeExpression Expression
                | Application Expression Expression
                | Variable Identifier
                deriving (Eq, Show)

data TypeExpression = Boolean | Integer | TypeExpression :->: TypeExpression deriving (Eq, Show)

parse :: String -> Either ParseError Expression
parse = Text.Parsec.parse application "" where
    application = foldl Application <$> primary <*> many (char ' ' *> primary)
    primary     = abstraction <|> literal <|> parameter <|> between (char '(') (char ')') application
    abstraction = Abstraction <$> (char '\\' *> many1 letter) <*> (char ':' *> typ) <*> (char '.' *> application)
    typ         = (Boolean <$ string "Bool") <|> Integer <$ string "Int" <|> foldr (:->:) <$> typ <*> many (string "->" *> typ)
    literal     = boolLiteral <|> intLiteral
    boolLiteral = BooleanLiteral . read <$> (string "True" <|> string "False")
    intLiteral  = IntegerLiteral . read <$> many1 digit
    parameter   = Variable <$> many1 letter