[Haskell-beginners] \x -> x < 0.5 && x > -0.5
mpm at alumni.caltech.edu
Mon Oct 19 22:48:50 EDT 2009
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
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.
The one suggestion I've seen here that seems to be right on the money is
liftM2 (&&) (< 0.5) (> -0.5)
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.
Or maybe this example is too small to be meaningful, but this kind of
abstraction is the direction I want to move in, for there are benefits
waiting for me when I arrive.
The Parsec library is an example of how concise and elegant code can get
when you choose your abstractions carefully.
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