buggy.elm

typeSignature =
    lazy <| \() ->
        sepBy (whitespace *> string "->" *> whitespace) nonFunctionType
        |> andThen (
            reducer TArrow
            >> Maybe.map succeed
            >> Maybe.withDefault (fail "expected type, got nothing")
        )

reducer : (a -> a -> a) -> List a -> Maybe a
reducer f list =
    case list of
        last :: [] ->
            Just last
        head :: tail ->
            reducer f tail
            |> Maybe.map (f head)
        [] ->
            Nothing

nonFunctionType : Parser s Type
nonFunctionType =
    let
        withArguments =
            TUnion
            <$> uppercaseName
            <*> (many onePartType)
    in
        or withArguments onePartType

onePartType : Parser s Type
onePartType =
    choice
        [ typeName
        , typeVar
        , parentheses
        --, tuple
        --, record
        ]

typeName : Parser s Type
typeName =
    (flip TUnion <| []) <$> uppercaseName

-- TODO: properly assign type variables
typeVar : Parser s Type
typeVar =
    always (TAny 1) <$> lowercaseName

parentheses : Parser s Type
parentheses =
    parens typeSignature