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|
module Operators (
primitives
) where
import Control.Monad.Except
import Error (LispError (..), LispResult (..))
import Parser
primitives :: [(String, [Expr] -> LispResult Expr)]
primitives =
[
("+", arithmetic (+))
, ("-", arithmetic (-))
, ("*", arithmetic (*))
, ("/", arithmetic (/))
, (">", comparator (>))
, ("<", comparator (<))
, (">=", comparator (>=))
, ("<=", comparator (<=))
, ("=", comparator (==))
, ("!=", comparator (/=))
]
data LispNumber = I Integer
| F Double
deriving (Eq, Ord)
instance Num LispNumber where
-- TODO:
-- float op anything = float
-- int op int = int
-- int op float = float
(I a) + (I b) = I $ a + b
(F a) + (F b) = F $ a + b
(I a) - (I b) = I $ a - b
(F a) - (F b) = F $ a - b
(I a) * (I b) = I $ a * b
(F a) * (F b) = F $ a * b
instance Fractional LispNumber where
(I a) / (I b) = I $ a `div` b
(F a) / (F b) = F $ a / b
arithmetic :: (LispNumber -> LispNumber -> LispNumber) -> [Expr] -> LispResult Expr
arithmetic op args
| length args < 2 = throwError $ ArgCount 2 args
| otherwise = do
as <- mapM unwrapNum args
return . wrapNum $ foldl1 op as
comparator :: (LispNumber -> LispNumber -> Bool) -> [Expr] -> LispResult Expr
comparator op args
| length args < 2 = throwError $ ArgCount 2 args
| otherwise = do
as <- mapM unwrapNum args
return . BoolLiteral . all (== True) $ zipWith op as (tail as)
unwrapNum :: Expr -> LispResult LispNumber
unwrapNum (IntLiteral n) = return $ I n
unwrapNum (FloatLiteral n) = return $ F n
unwrapNum x = throwError $ TypeMismatch "number" x
wrapNum :: LispNumber -> Expr
wrapNum (I n) = IntLiteral n
wrapNum (F n) = FloatLiteral n
|
