Proposal: Add "fma" to the RealFloat class

Carter Schonwald carter.schonwald at
Sat May 2 02:47:06 UTC 2015

well said brandon.  FMA support is absolutely a mathematical accuracy and
 performance engineering thing (except when it hinder performance ).  It is
worth noting that most modern CPUS support several *different* versions of
the FMA operation, but thats beyond the scope / goal of this proposal I

but yeah, for all of Num's warts, probably the right place to put it, with
a default implementation in terms of * and + (and compiler supplied primops
for applicable prelude types)

On Fri, May 1, 2015 at 2:11 PM, Brandon Allbery <allbery.b at> wrote:

> On Fri, May 1, 2015 at 5:52 PM, David Feuer <david.feuer at> wrote:
>> I'm somewhat opposed to the Num class in general, and very much opposed
>> to calling floating point representations "numbers" in particular. How are
>> they numbers when they don't obey associative or distributive laws, let
>> alone cancellation, commutativity, ....? I know Carter
> TBH I think Num is a lost cause. If you want mathematical numbers, set up
> a parallel class instead of trying to force a class designed for numbers
> "in the wild" to be a pure theory class.
> This operation in particular is *all about* numbers in the wild --- it has
> no place in theory, it's an optimization for hardware implementations.
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at
> ballbery at
> unix, openafs, kerberos, infrastructure, xmonad
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