Hi All,

 

I'm trying to work out how to show the steps in evaluating "How the function is calculated". In other words I want this program to actually print out the steps. For e.g. eval (Multiply(Add(Val 10) (Val 20)) (Val 3)    Which is add 10+20 and multiply by 3 = 90

 

The program then produces( Prints out) something like

 

working: eval (Multiply(Add(Val 10) (Val 20)) (Val 3)  

working Add(Val10) (Val 20)

answer 1 Val 30

answer 2 Val 90

 

This is what I have so far but it wont even do the calculations. Any help appreciated.

 

data Expression = Val Float
                | Add Expression Expression
                | Subtract Expression Expression
                | Multiply Expression Expression
                | Divide Expression Expression
         deriving Show

eval :: Expression -> Float
eval (Val x) = x
eval (Add x y) = eval x + eval y
eval (Multiply x y) = eval x * eval y
eval (Subtract x y) = eval x - eval y
eval (Divide x y) = eval x / eval y

 

 

 

John