Make Eq type class single method

[Joachim Breitner]

Hi,

Am Mittwoch, dem 20.10.2021 um 16:08 +0100 schrieb Tom Ellis:
> Since (/=) is an Eq class method it can be implemented on (Int, Int)
> as
> 
>   (x1, x2) /= (y1, y2) = (x1 /= y1) || (x2 /= y2)
> 
> If it were not a class method it would have to be implemented as,
> after inlining
> 
>   (x1, x2) /= (y1, y2) = not ((x1 == y1) && (x2 == y2))
> 
> Might not the latter be less efficient, because of the extra `not`?

maybe. I think I’ll simply try it out, and see if for example GHC
itself speeds up if (/=) is not a class method.

Note that if the inner Eq is using the default implementation, then
there will be _two_ not there.

I’d expect that not will quickly inline, and the cost of an inlined not
might be small compared to the cost of projecting (/=) out of the class
dictionary (in polymorphic code). And in other cases, the (/=) might
inline and the not might be fused with the surrounding code via case-
of-case. 

Cheers,
Joachim
-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/