Am Dienstag 20 Oktober 2009 04:48:50 schrieb Michael Mossey:
Carl Cravens wrote:
Michael Mossey wrote:
Is there a nifty way to write
filter (\x -> x < 0.5 && x > -0.5) xs
without explicitly using x?
I'm pretty new to Haskell... are you looking for a *better* way to write this, or is this an exercise in exploring alternatives for the sake of understanding?
Hi Carl,
Either one.
Let me chime in with some observations from a few months of studying Haskell. (Brent and Apfelmus can probably elaborate on this.)
Eliminating variables and working with function combinations has benefits.
But it's not unconditionally a good thing. If you exaggerate it, it's pure obfuscation. Nevertheless, playing around with eliminating variables and using combinators even beyond the border of obfuscation is a good exercise. You gain understanding and a feeling of when it's better to stop by that.
The one suggestion I've seen here that seems to be right on the money is
liftM2 (&&) (< 0.5) (> -0.5)
May I offer (&&) <$> (< 0.5) <*> (> -0.5) ? It works on Applicative Functors (doesn't need the full force of Monads).
Although that might seem less clear to a beginner, it is actually _more_ clear than the lambda function in some ways. It's easier to work with proof at a more abstract level like this, and strange as it may seem, what I seem to observe in expert users of Haskell is that their brains will pick up what this is doing faster than the lambda function.
In this small example, both are immediately clear, you need more complicated lambda expressions to get a measurable difference :)