[Haskell-cafe] Haskell Cheat Sheet?
jcast at ou.edu
Wed Sep 26 11:39:22 EDT 2007
On Tue, 2007-09-25 at 17:19 -0700, Dan Weston wrote:
> One suggestion:
> Section 3.6 defines a function "fix":
> fix :: Eq x => (x -> x) -> x -> x
> fix f x = if x == x' then x else fix f x'
> where x' = f x
> This confusingly differs in both type and meaning from the traditional
> function Control.Monad.Fix.fix and is not even used elsewhere in the
> I suggest that it be removed and the real Control.Monad.Fix.fix function
> be defined in its own section, with an side-by-side comparison with a
> named recursive function. This would be useful because the type
> fix :: (a -> a) -> a
> is highly confusing, suggesting to newcomers a usage like:
> f = fix (+1)
> which is undefined (and seems to be "missing an argument"), when
> invariably its type is in practice restricted to:
> fix :: ((a -> b) -> (a -> b)) -> (a -> b)
> which is much more suggestive (but nowhere to be found in the docs).
Not invariably. I frequently use fix at monadic types, sometimes with
an argument but not always.
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