At 9:20 PM -0500 10/22/03, Pratik Bhadra wrote:
Hi
I have a data type Expr for handling Expressions
data Expr = Lit1 Int | Lit2 Bool | Var String | BinOp Op Expr Expr
As you can see, I am trying to have an Expression have both Int and Bool values so that I can work with both arithmetic (+,-,*,/) and logical(and,or,<,<=,>,>=) operators.
That makes sense.
What I am aiming at is to parse a line which contains an expression, evaluate it and return the result. I am facing some problems in this regard. When I write the evaluate function, the Haskell compiler refuses to compile my code as it says, instance of Num Expr required. Any ideas what I am supposed to do to fix that?
I think that's the same question I answered in my previous email. Right? It's saying that Expr needs to be an instance of Num, because (+), or some other numeric operation, is being applied to an Expr. --HR -- ------------------------------------------------------------------ Hamilton Richards, PhD Department of Computer Sciences Senior Lecturer The University of Texas at Austin 512-471-9525 1 University Station C0500 Taylor Hall 5.138 Austin, Texas 78712-1188 ham@cs.utexas.edu hrichrds@swbell.net ------------------------------------------------------------------