Haskell-book/11/Hutton.hs


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module Hutton where

data Expr
    = Lit Integer
    | Add Expr Expr

eval :: Expr -> Integer
eval (Lit x)   = x
eval (Add x y) = (eval x) + (eval y)

printExpr :: Expr -> String
printExpr (Lit x) = show x
printExpr (Add x y) = (printExpr x) ++ " + " ++ (printExpr y)