Re: [Haskell-beginners] How to avoid evaluating the second (undefined) argument of a Boolean AND operation?

On Wed, Jun 22, 2011 at 8:07 PM, Jack Henahan wrote:

Use

   myAND F _ = F

instead of using x.

Actually that doesn't change anything and both definitions are the same thing. The problem here is that "type checking is not lazy" =). The second argument of myAND in "myAND F (1/0)" isn't being evaluated at all; actually your code isn't running at all. What is being reported is a type error, not a runtime error. Try one of these instead: myAND F undefined myAND F (error "foo") myAND F (let x = x in x) myAND F (unsafePerformIO $ launchMissiles) Cheers! =) -- Felipe.