FP Laboratory 9

User defined data types and type classes

Consider following representation of expressions

data Expr = Num Int
          | Add Expr Expr
	  | Sub Expr Expr
	  | Mul Expr Expr
	  | Div Expr Expr
	  | Var Char
	  deriving (Eq)

• Create function eval that evaluates expresions.
• Create function showExpr that shows expression as a String.
• Extend class Show to be usable with our expressions.
• Create function derivation representing symbolic derivation of a given expression.