| I am looking for some advice on | where to place specialize-pragmas for ghc | (to optimize speed - and heap usage) | | Typically I have some module A (containing polymorphic functions A.f, ..) | and a module B uses this. The interesting case is | when I want to specialize A.f (which is NOT exported) | to some types that are only defined in B | (but normally A should not know about B). | | Is there some kind of `deep specialisation' where one would say, | `specialize ALL the functions that are reachable from here'? - | or how can one get a similar effect? There are two questions here a) If module B defines a type B.T, and imports function A.f from module A can we specialise f at type B.T? b) If we specialise f at T, and f calls g, how can we specialise g at T? Unfortunately, GHC has no good way to do (a). It only specialises functions in the module being compiled, so it can't specialise f when compiling A because it can't see B.T it can't specialise f when compiling B because it can't see (all of) f It's not obvious how best to address this. Putting all of A's code in its interface file (not only f, but the things f calls), so that B can specialise it, seems a bit brutal; and f might then be specialised to the same type many times. But we can't specialise it in module A, because A can't see T. Maybe the Right Thing is some kind of whole-program specialisation, but GHC isn't set up to do that. The only workaround is to define T early, import it into A, and specialise A.f there. Relating to (b), GHC automatically does this specialisation propagation within one module, but if A.f calls A2.g (where A imports A2), then A2.g won't get automatically specialised; you'll have to add your own specialisation pragma in A2. Again this is far from ideal. One possible plan (totally unimplemented) is this: when compiling a module, dump specialisation guidance of the form A.f needs A2.g @ T or, more generally something like A.f @ t needs A2.g at [t] Now do a global analysis of all the specialization guidance info to generate SPECIALISE pragamas. Now recompile everything Simon