Scherrer, Chad wrote:
module Main where import A import B main = A.f >> B.f
module A where f = ...
module B where f = ...
in a single file. This example is straight from chapter 5 of the Report, and no mention is made (that I could find) about modules needing to be in separate files. But this won't load in ghci! (Even if ... is changed to putStr "hi"). Eventually I figured out that it works fine if it's split over three separate files.
The report says that they make up a single program, so that does not imply that they are in a single file. But, you are right: it's a good idea to be explicit about this.
So here's what I'm trying to figure out: If every file corresponds to exactly one module (is that true?), then why must the module name be given again in the text of the file? When I'm using ghci, I have lots of modules that I sometimes want to load "as Main", and sometimes I only want them loaded as a dependency from another module. Currently, I have to go into each file to change the "module Foo where" line to do this.
Section 9.5 of the report seems to show that <module> stands for the compilation unit and it defines a single module. I suppose the standard allows you to name your module freely no matter your filesystem allows, but ghc requires (afaik) that module M exist in M.hs or M.lhs. Why not do this: name none of those modules Main.hs, and have an empty module Main.hs with only "import MainDeJour" and "main = MainDeJour.main" so you can just edit just that file. Cheers, Koray