70 lines
1.6 KiB
Agda
70 lines
1.6 KiB
Agda
module Parser
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import Prelude
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import Aoc
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Parser : U → U
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Parser a = List Char → Either String (a × List Char)
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instance Monad Parser where
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pure a = \ cs => Right (a, cs)
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bind ma mab = \ cs => ma cs >>= uncurry mab
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instance Alternative Parser where
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pa <|> pb = \ cs => case pa cs of
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Left msg => pb cs
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res => res
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instance Functor Parser where
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map f pa = \ cs => case pa cs of
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Left msg => Left msg
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Right (a, cs) => Right (f a, cs)
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instance Applicative Parser where
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return a = pure a
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pa <*> pb = pa >>= (\ f => map f pb)
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fail : ∀ a. String -> Parser a
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fail msg = \ cs => Left msg
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-- TODO, case builder isn't expanding Parser Unit to count lambdas
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eof : Parser Unit
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eof = \ cs => case cs of
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Nil => Right (MkUnit, Nil)
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_ => Left "expected eof"
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satisfy : (Char → Bool) → Parser Char
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satisfy pred = λ cs => case cs of
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Nil => Left "unexpected EOF"
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(c :: cs) => if pred c then Right (c, cs) else Left ("did not expect " ++ show c)
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match : Char → Parser Char
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match d = satisfy (_==_ d)
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any : Parser Char
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any = satisfy (λ _ => True)
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some many : ∀ a. Parser a → Parser (List a)
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many p = some p <|> pure Nil
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some p = do
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v <- p
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vs <- many p
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pure (v :: vs)
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string : String → Parser Unit
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string str = go (unpack str)
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where
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go : List Char → Parser Unit
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go Nil = pure MkUnit
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go (c :: cs) = match c >> go cs
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number : Parser Int
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number = stringToInt ∘ pack <$> some (satisfy isDigit)
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-- do
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-- digs <- some (satisfy isDigit)
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-- pure $ stringToInt $ pack digs
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ws : Parser Unit
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ws = many (match ' ') >> pure MkUnit
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