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@joachim-breitner.de http://www.joachim-breitner.de/