Hi

   I'm trying to get a if statement to work but not sure if this is the right approach, what I want to do in simple english is to evaluate  one expression at a time for example. (3+2)+(4+5) I want it to return 5 + (4+5) then 5+9.

 

data Expression = Val Integer
                | Add Expression Expression
                | Subtract Expression Expression
                | Multiply Expression Expression
                | Divide Expression Expression
         deriving Show
evalStep :: Expression ->  Expression
evalStep (Val x)=  (Val x) 

evalStep (Add x y) = do
              
  if x = isDigit
           then if y isDigit
             else evalStep x,y

 

I thinking about using recursion down a tree left then right but that seems very complicated.

Any thoughts welcome!

John