CODEWITHSUNDEEP
haskell
Nayana
Nayana

Reputation: 1549

Haskell, parse error

Everyone. I am fairly new to Haskell.

I am getting this indentation error, but I have no idea why I am getting it. I indicated from which line I am getting this error by a comment.

And if you could help me correct my "func" and "call", I'd greatly appreciate it. 

import Data.Maybe 

data Operator = Add | Sub | Mul | Div | And | Or | Not | Eq | Less | Great
  deriving (Eq, Show)
data Expression = Literal Val
            | Prim Operator [Expression]
            | Variable String
            | If Expression Expression Expression
            | Let [(String, Expression)] Expression
        | Func [String] Expression
        | Call Expression [Expression]
  deriving (Show, Eq)

data Val = Num Int
           | Bool Bool
       | Closure [String] Expression Environment
  deriving (Eq, Show)

type Environment = [(String, Val)]
--20
primitive :: Operator -> [Val] -> Val
primitive Add [Num a, Num b] = Num (a+b)
primitive Mul [Num a, Num b] = Num (a*b)
primitive Sub [Num a, Num b] = Num (a-b)
primitive Div [Num a, Num b] = Num (a `div` b)
primitive And [Bool a, Bool b] = Bool (a && b)
primitive Or [Bool a, Bool b] = Bool (a || b)
primitive Not [Bool a] = Bool (not a)
primitive Eq [a, b] = Bool (a == b)
primitive Less [Num a, Num b] = Bool (a < b)
primitive Great [Num a, Num b] = Bool (a > b)
--32
evaluate :: Environment -> Expression -> Val
evaluate e (Literal v)  = v
evaluate e (Prim op as) = primitive op (map (evaluate e) as)
evaluate e (Variable x) = fromJust (lookup x e)
evaluate e (If a b c)   = evaluate e (if fromBool (evaluate e a) then b else c)
evaluate e (Let bp b)   = evaluate ([(x, evaluate e d) | (x,d) <- bp ] ++ e) b

evaluate e (Func str ex) = str ex e
evaluate e (Call ex exl) = [[a, b, c ++ (map (evaluate e) exl)] | (a, b, c)<-(evaluate e ex)] --41
--42
fromBool (Bool b) = b

main = do
   let x = Variable "x"
       func1 = x*2 -- this is where I am getting a "parse error (possibly incorrect indentation)"
       func2 = x*5
    in print(evaluate [("r",Num 7)] (Call (If (Bool True) func1 func2) [Num 5]))

Upvotes: 1

Views: 922

Answers (1)

Mihai Maruseac
Mihai Maruseac

Reputation: 21425

You have several problems with your code. First, the let Int x is wrong. The syntax of let is let value = expression in expression (or a list of value = expression). Your Int x doesn't match this syntax. This is what confuses the compiler making it report indentation error.

Also, you have used fun1 and fun2 in the last line, even though they are not in scope.

Upvotes: 3

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