base package (Was: GHC 7.8 release?)

Ian Lynagh ian at
Wed Feb 20 18:12:10 CET 2013

On Fri, Feb 15, 2013 at 02:45:19PM +0000, Simon Marlow wrote:
> Remember that fingerprinting is not hashing.  For fingerprinting we
> need to have a realistic expectation of no collisions.  I don't
> think FNV is suitable.
> I'm sure it would be possible to replace the C md5 code with some
> Haskell.  Performance *is* important here though - Typeable is in
> the inner loop of certain generic programming libraries, like SYB.

We currently just compare
for equality, right? Could we instead compare
    (hash str, str)
? That would be even more correct, even if a bad/cheap hash function is
used, and would only be slower for the case where the types match
(unless you're unlucky and get a hash collision).

In fact, we may be able to arrange it so that in the equal case the
strings are normally exactly the same string, so we can do a cheap
pointer equality test (like ByteString already does) to make the equal
case fast too (falling back to actually checking the strings are equal,
if they aren't the same string).


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