[Haskell-cafe] Hoogle? [Stacking monads]
andrewcoppin at btinternet.com
Fri Oct 3 14:09:28 EDT 2008
Andrew Coppin wrote:
> After much searching (Hoogle rather failed me here), I discover that...
I could probably elaborate on that point further.
Try doing a Hoogle search for "c1 (c2 x) -> c2 (c1 x)". Hoogle correctly
states that Data.Traversable.sequence will do it for you.
Now try doing "c1 k (c2 x) -> c2 (c1 k x)". The 'sequence' function will
also do this, but now Hoogle returns 0 results.
This is puzzling, since AFAIK, the above two type signatures are
"equvilent" in some sense. (Specifically, replace every type X with type
Y and you get from one to the other.) To me, this looks like a Hoogle
bug. (It goes without saying that Hoogle also failed to find anything
for the more specific type signature I was searching for, despite the
fact that 'sequence' unifies with it.)
Is this a known issue?
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