[Haskell] Re: sizeFM type

ajb at spamcop.net ajb at spamcop.net
Mon Apr 26 22:06:29 EDT 2004

G'day all.

Quoting "S. Alexander Jacobson" <alex at i2x.com>:

> I'll cite that hoary Hoare quotation here.
> "Premature optimization is the root of all evil."

Agreed!  In particular, functions meant for general use, especially in
the standard library, should not optimise for a specific case and
pessimise for all other cases.  Much evil has budded from library
implementors who thought they knew better than application programmers
about what performance models were appropriate.  (If you don't believe
me, ask a C++ developer about reference-counted strings and multi-
threading some time.)

Making sizeFM return Integer optimises the operation for cases where the
FiniteMaps are extremely huge and pessimises it for all cases where the
FiniteMaps are not extremely huge.  Not only is this premature optimisation,
it's optimising for the empirically LEAST likely case.

Now that I think of it, it would make far more sense for the type to be
completely general:

    sizeFM :: (Ord key, Integral size) => FiniteMap key elt -> size

This way, sizeFM can optimise itself for the situation at hand.

Andrew Bromage

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