我是Haskell的新手,我正在努力調試我的代碼。 修復錯誤導致其他錯誤...由於使用`/'而沒有出現(Fractional Int)實例
這是我的代碼。
import Data.Maybe
data Op = Add | Sub | Mul | Div | And | Or | Not | Eq | Less | Great
deriving (Eq, Show)
data Exp = Literal Value
| Primitive Op [Exp]
| Variable String
| If Exp Exp Exp
| Let [(String, Exp)] Exp
deriving (Show, Eq)
data Value = Number Int
| Bool Bool
| String String
deriving (Eq, Show)
type Env = [(String, Value)]
eval :: Env -> Exp -> Value
eval e (Literal v) = v
eval e (Variable x) = fromJust (lookup x e) --22
prim :: Op -> [Value] -> Value
prim Add [Number a, Number b] = Number (a + b)
prim And [Bool a, Bool b] = Bool (a && b)
prim Sub [Number a, Nuamber b] = Number (a - b) -- No instance for (Fractional Int) arising from a use of `/'
prim Mul [Number a, Number b] = Number (a * b)
prim Div [Number a, Number b] = Number (a/b)
prim Or [Bool a, Bool b] = Bool (a || b)
prim Not [Bool a] = Bool (not a)
prim Eq [Number a, Number b] = Bool (a == b)
prim Eq [String a, String b] = Bool (a == b)
prim Less [Number a, Number b] = Bool (a < b)
prim Less [String a, String b] = Bool (a < b)
prim Great [Number a, Number b] = Bool (a > b)
prim Great [String a, String b] = Bool (a > b) --37
main = do
eval [("y", (Number 40))] (Let [("x", (Literal (Number 2)))] (prim Add [(Variable "x"), (Variable "y")])) -- Couldn't match expected type `Exp' with actual type `Value'
我現在收到了兩條我在評論中寫到的錯誤。 如果您知道我的代碼有什麼問題,請分享您的想法並節省我的時間...
非常感謝。
你是不是指'Number(div a b)'或者它的中綴版本? –