[Haskell-cafe] Class-like features for explicit arguments
Ertugrul Söylemez
ertesx at gmx.de
Sat Apr 25 18:12:22 UTC 2015
> Likewise, to what extent aside from syntactic nicety does implicit
> parameters and the punning extensions not suffice?
At the definition and instantiation sites I mostly miss defaults. At
the application sites I would love to have specialisation for certain
arguments. For example I would like to be able to tell GHC that I would
like to have a version of my function `f` with a certain argument
inlined. Note that I don't want to inline `f` itself. Rather I'd like
to preapply certain arguments:
f :: X -> Y -> Z
{-# SPECIALISE f SomeX #-}
{-# SPECIALISE f SomeOtherX #-}
This would generate two specialised versions of `f` with exactly the
given arguments inlined. That way I can get a very efficient `f`
without having to inline it at the application sites. And as long as
`f` is INLINABLE I can put those pragmas pretty much everywhere. I
believe this is exactly what happens for type class dictionaries.
This can (and probably should) be a separate feature though. For some
of my applications I need to inline a huge chunk of code multiple times
to compensate for the lack of this feature.
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