Created
May 14, 2017 09:59
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| module Parser where | |
| import Control.Applicative | |
| import Control.Monad | |
| import Control.Monad.Trans.State | |
| import Data.Char | |
| type Parser a = StateT String Maybe a | |
| runParse :: Parser a -> String -> Maybe a | |
| runParse p s = do (a,b) <- runStateT p s | |
| guard (null b) | |
| return a | |
| item :: Parser Char | |
| item = do s <- get | |
| guard (not (null s)) | |
| put (tail s) | |
| return (head s) | |
| test :: Parser a -> (a -> Bool) -> Parser a | |
| test m p = do a <- m | |
| guard (p a) | |
| return a | |
| sat :: (Char -> Bool) -> Parser Char | |
| sat = test item | |
| char :: Char -> Parser Char | |
| char = sat . (==) | |
| letter :: Parser String | |
| letter = some (sat isAlpha) | |
| int :: Parser Int | |
| int = do sign <- (char '-' >> pure negate) <|> pure id | |
| num <- read <$> some (sat isDigit) | |
| return (sign num) | |
| oneOf :: String -> Parser Char | |
| oneOf = sat . flip elem | |
| notIn :: String -> Parser Char | |
| notIn = sat . flip notElem | |
| token :: Parser a -> Parser a | |
| token = (>>) spaces | |
| where spaces = many $ sat isSpace | |
| type Env = Map.Map String Expr | |
| type Fun = [Expr] -> Expr | |
| data Expr = Symbol String | |
| | String String | |
| | Number Int | |
| | Bool Bool | |
| | List [Expr] | |
| | Closure Env Expr | |
| deriving (Show) | |
| nil :: Expr | |
| nil = List [] | |
| symbol :: Parser Expr | |
| symbol = Symbol <$> s | |
| where s = some $ notIn " \r\n\"\'#()" | |
| string :: Parser Expr | |
| string = String <$> (char '"' *> letter <* char '"') | |
| number :: Parser Expr | |
| number = Number <$> int | |
| bool :: Parser Expr | |
| bool = Bool <$> (char '#' *> (t <|> f)) | |
| where t = char 't' >> pure True | |
| f = char 'f' >> pure False | |
| list :: Parser Expr | |
| list = List <$> (char '(' *> x <* char ')') | |
| where x = many $ token expr | |
| expr :: Parser Expr | |
| expr = string <|> bool <|> number <|> symbol <|> list | |
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