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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 div)
]
arithmetic :: (Integer -> Integer -> Integer) -> [Expr] -> LispResult Expr
arithmetic op args
| length args < 2 = throwError $ ArgCount 2 args
| otherwise = do
as <- mapM unwrapNum args
return . IntLiteral $ foldl1 op as
unwrapNum :: Expr -> LispResult Integer
unwrapNum (IntLiteral n) = return n
unwrapNum x = throwError $ TypeMismatch "number" x
|
