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 document.
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. jcc