[Haskell-cafe] Things to avoid (Was: Top 20 ``things'' to know
lemming at henning-thielemann.de
Fri Feb 11 05:14:40 EST 2005
On Fri, 11 Feb 2005, Remi Turk wrote:
> 1) It's talking about the compiler having difficulty with some
> warnings when using guards.
> f x | odd x = ...
> | even x = ...
> GHC does complain. I would also call it Bad Code,
> but if it's what you mean, _this_ example should be in the
Yes, your example is better.
> 2) foo xs | length xs == 1 = bar (head xs)
> As already said in "Don't ask for the length of a list, if you
> don't need it", this usage of length is bad in itself, and
> doesn't really help the argument against patterns IMO.
I have seen it similarly in the example I give below at that page. So I
found it worth noting that some guards can nicely be replaced by simple
patterns. More examples are welcome. May be we should replace it by
foo xs | not (null xs) = bar (head xs)
foo (x:_) = bar x
This example might be useful, too:
foo x | x == 0 = blub
x /= 0 = bla
foo 0 = blub
foo _ = bla
> 3) the pattern guards extension.
> I have two objections against this one. First, I don't think
> it's a good idea to talk about a non-standard extension like
> pattern guards in a wiki about newbie-problems.
It was given to me as a good example why Guards are invaluable:
> P.P.S. Does a piece about "Avoid explicit lambda's" stand any
> chance of not being removed?
> (Basically about "\x y -> x + y" vs "(+)", and "when it
> gets more complicated it probably deserves a name.")
More information about the Haskell-Cafe