[Haskell-beginners] Re: if statements

25 Jan 2010


      John Moore schrieb:
...
data Expression = Val Integer
                | Add Expression Expression
                | Subtract Expression Expression
                | Multiply Expression Expression
                | Divide Expression Expression
         deriving Show
After you've copied your code (several times) for the four cases
Add, Subtract, Multiply, and Divide, you may want to consider:

data Expression = Val Integer
   | OpExpr Op Expression Expression

data Op = Add | Subtract | Multiply | Divide

op2op :: Op -> Integer -> Integer -> Integer
op2op op = case op of
   Add -> (+)
   Subtract -> (-)
   Multiply -> (*)
   Divide -> div

(or: type Op = Integer -> Integer -> Integer)

Cheers Christian

[Haskell-beginners] Re: if statements

Christian Maeder