"Neil Mitchell" <[EMAIL PROTECTED]> writes: > Hi > > Haskell is great for equational reasoning. > > > blah the_v_in_scope blah > > where (the_v_in_scope:_) = [ v | (n,v) <- env, n==target ] > > This piece of code isn't.
Strange. It's semantically the same, isn't it? Indeed, the definition of head gets you to it. > If you used head then you could trivially inline > the_v_in_scope, this way is a lot harder. I don't follow that at all. I don't do inlining, the compiler does. Or are you talking about the inlining that was originally there and my version explicitly removed? > You might spot a pointfree pattern and lift it up. You > might move code around more freely. Lots of patterns like > this breaks the equational reasoning in the style that > most people are used to. To convince me of that, you'd have to convince me that (head []) doesn't break the equational reasoning. > > and it doesn't seem /that/ great an imposition. > > I disagree, this is a massive imposition, and requires > lots of refactoring, "lots" is in the eye of the beholder. You only have to do this where you would have used head -- and if you can already /prove/ that head won't fail, there's no reason to replace it. So it's only necessary in cases where the proof is absent. > and is just a little bit ugly. Sure, I don't dispute that. I was merely suggesting that one can already do this for the uncertain cases, rather than have to invoke a whole other set of new machinery just to get a line number in the error message. Your headNote is a good approach, but it strikes me that it's a bit redundant. Instead of “headNote "foo"” just use “headDef (error "foo")”. It's a wee bit longer, but having the “error” out there in the open seems more honest somehow, and there would be fewer function names to remember. -- Jón Fairbairn [EMAIL PROTECTED] _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
