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module Parser (Parser, item, digit, run) where | |
import Data.Int (fromString) | |
import Data.Maybe (fromJust, Maybe(..)) | |
import Data.String.CodeUnits (charAt, drop, singleton) | |
import Data.Tuple (Tuple(..)) | |
import Partial.Unsafe (unsafePartial) | |
import Prelude | |
newtype Parser a = Parser (String -> Array (Tuple a String)) | |
item :: Parser Char | |
item = Parser $ case _ of | |
"" -> [] | |
string -> [Tuple (unsafePartial $ fromJust $ charAt 0 string) (drop 1 string)] | |
run :: forall a. Parser a -> String -> Array (Tuple a String) | |
run (Parser parse) string = parse string | |
instance functorParser :: Functor Parser where | |
map :: forall a b. (a -> b) -> Parser a -> Parser b | |
map f (Parser parse) = Parser $ \string -> | |
case parse string of | |
[Tuple a rest] -> [Tuple (f a) rest] | |
_ -> [] | |
instance applyParser :: Apply Parser where | |
apply :: forall a b. Parser (a -> b) -> Parser a -> Parser b | |
apply (Parser f) (Parser parse) = Parser $ \string -> | |
case f string of | |
[Tuple fn rest] -> case parse rest of | |
[Tuple b rest'] -> [Tuple (fn b) rest'] | |
_ -> [] | |
_ -> [] | |
instance monadParser :: Bind Parser where | |
bind :: forall a b. Parser a -> (a -> Parser b) -> Parser b | |
bind (Parser parse) f = Parser $ \string -> | |
case parse string of | |
[Tuple x remaining] -> case (f x) of | |
(Parser parse') -> case parse' remaining of | |
[Tuple x' remaining'] -> [Tuple x' remaining'] | |
_ -> [] | |
_ -> [] | |
success :: forall a. a -> Parser a | |
success a = Parser \string -> [Tuple a string] | |
fail :: forall a. Parser a | |
fail = Parser \string -> [] | |
digit :: Parser Int | |
digit = do | |
x <- item | |
case fromString $ singleton x of | |
Just num -> success num | |
Nothing -> fail |
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