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module Parser ( parseLispValue
, Expr(..)
, parseString
, parseInt
, parseFloat
, parseId
, parseQuote
) where
import Control.Applicative ((<$>))
import Control.Monad (liftM)
import Text.ParserCombinators.Parsec
-- TODO: use LispNumber (src/Operators.hs) here instead of IntLiteral and FloatLiteral
-- TODO: add character literals: \#a \#b \#c \#space \#newline
-- TODO: add support for complex numbers, oct and hex numbers
data Expr = List [Expr]
| DottedList [Expr] Expr
| StringLiteral String
| IntLiteral Integer
| FloatLiteral Double
| BoolLiteral Bool
| Id String
deriving (Eq)
-- backslash double quote escapes a quote inside strings
quotedChar = noneOf ['\"'] <|> try (string "\\\"" >> return '"')
parseString :: Parser Expr
parseString = do
char '"'
innards <- many quotedChar
char '"'
return (StringLiteral innards)
parseSign :: Parser (Maybe Char)
parseSign = do
sign <- optionMaybe (oneOf "+-")
return $ case sign of
Just '+' -> Nothing
s -> s
parseInt :: Parser Expr
parseInt = do
sign <- parseSign
val <- many1 digit
return $ (IntLiteral . read) $ maybe val (:val) sign
parseFloat :: Parser Expr
parseFloat = do
sign <- parseSign
characteristic <- many1 digit
char '.'
mantissa <- many1 digit
let fval = characteristic ++ "." ++ mantissa
return $ (FloatLiteral . read) $ maybe fval (:fval) sign
symbol :: Parser Char
symbol = oneOf "!#$%&|*+:/-=<?>@^_~"
parseId :: Parser Expr
parseId = do
first <- letter <|> symbol
rest <- many (letter <|> symbol <|> digit)
let atom = first:rest
return $ case atom of
"#t" -> BoolLiteral True
"#f" -> BoolLiteral False
_ -> Id atom
whiteSpace :: Parser ()
whiteSpace = skipMany1 space
type Alias = String
parseModifier :: Char -> Alias -> Parser Expr
parseModifier c alias = do
char c
x <- parseLispValue
return $ List [Id alias, x]
parseQuote = parseModifier '\'' "quote"
parseQuasiquote = parseModifier '`' "quasiquote"
parseUnquote = parseModifier ',' "unquote"
-- TODO: add modifier for unquote splicing: ,@
parseLispValue :: Parser Expr
parseLispValue =
parseString
<|> try parseFloat
<|> try parseInt
<|> try parseId
<|> parseQuote
<|> parseQuasiquote
<|> parseUnquote
-- handles lists and dotted lists
<|> do
char '(' >> spaces
x <- sepEndBy parseLispValue whiteSpace
spaces
t <- optionMaybe $ space >> char '.' >> space >> parseLispValue
spaces >> char ')'
return $ maybe (List x) (DottedList x) t
<?> "lisp value"
showLispList :: [Expr] -> String
showLispList = unwords . map show
instance Show Expr where
show (DottedList xs x) = "(" ++ showLispList xs ++ " . " ++ show x ++ ")"
show (List xs) = "(" ++ showLispList xs ++ ")"
show (StringLiteral s) = "\"" ++ s ++ "\""
show (IntLiteral n) = show n
show (FloatLiteral n) = show n
show (BoolLiteral True) = "#t"
show (BoolLiteral False) = "#f"
show (Id i) = i
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