Andrew J Bromage
G'day all.
On Wed, Feb 05, 2003 at 08:05:56PM -0600, Jon Cast wrote:
I'm not sure I follow this. If you change the type of a value exported from a given module, that's a public change, no? And if you don't, why should re-compilation be needed?
Consider this:
<< module A where
import B
{- use B.b -}
<< module B (b) where
import C
b = C.c
<< module C (c) where
c :: Int
Changing the type of c requires recompiling module A.
You would expect that changing c's type forces a recompilation of B, since you changed C's public interface. However, this also changes B's public interface even though you did not touch the text of module B. The reason is that B's public interface is partly based on modules which it _privately_ imports, even if it does not re-export any symbols from those modules.
I think I see what you're saying. I still maintain, however, that, since you've changed the type of B.b (admittedly implicitly), and B.b is exported from B, that you've changed B's interface. There is a reason make is designed to re-build B /and/ (potentially) A when C changes, after all.
One fix is to require all exported symbols to have explicit type declarations. Since this is good practice anyway, I would be in favour of making it a language requirement in Haskell 2.
Cheers, Andrew Bromage
Jon Cast