On 28 July 2010 13:57, Sebastian Fischer
In my case, I don't want to put everything in a single module because I cannot know what other B-like modules people will implement.Are they bound to use `f` unspecialized for their types?
Yes. GHC might inline "f" into the call site and achieve specialisation that way, but AFAIK there is no way to force this.
Why?
SPECIALISE pragmas are not supported in any but the defining module because the Core for a function to specialise is not guaranteed to be available in any other module. I don't think there is any other barrier. It is possible to imagine implementing a remedy for this by using -fexpose-all-unfoldings and having GHC use the exposed Core to generate a specialisation in any importing module. You would probably also want some sort of mechanism to "common up" specialisations if several modules independently specialise one function to the same type (could do this in the linker or even earlier). You would probably also have to be prepared to emit warnings about stuff like this: """ module A where import B f :: Foo a => a -> a f = ... """ """ module B import {-# SOURCE #-} A newtype Bar = ... instance Foo Bar where {-# SPECIALISE f :: Bar -> Bar #-} """ Another nice-to-have along the same lines is something like this: """ map_unboxed :: [Int#] -> [Int#] map_unboxed = map (+# 1) """ i.e. allow polymorphic functions to be instantiated at types of a kind other than *. This would be a rather cool and useful feature :-). As far as I know noone is working on either of these features. Cheers, Max