Why don't we put "fix" into another library, and let MonadRec Arrow, etc. import it? Fixed-point operators show up quite often to deserve a library of their own: If all I care about is "fix", I shouldn't be forced to "import MonadRec". This new library can include various flavors of fix:
fix :: (a -> a) -> a -- usual fixed-points fix f = let a = f a in a
nthApprox :: Integer -> (a -> a) -> a -- approximations to fix nthApprox n f = (iterate f undefined) !! n
trace :: ((a, u) -> (b, u)) -> (a, b) -- traces trace f a = let (b, u) in f (a, u) in b
pFix :: ((a, u) -> u) -> (a -> u) -- parameterized fix pFix f a = let (a, u) = f u in u
Then MonadRec, Arrow, or whoever just needs fixed-point operators can import it from there..
This sounds fine to me. It should probably go in Control.Fix. Levent: would you like to suggest a full contents for this library? Cheers, Simon