[Haskell-cafe] Cyclic Inclusions

C.M.Brown cmb21 at kent.ac.uk
Tue Aug 12 13:38:11 EDT 2008

> The problem is not mutually recursive modules.  Plenty of statically
> typed languages support mutually recursive modules.
> The problem is that it's impossible in general to say what the
> "interface" of a module is by examining the module alone.  This is a
> very unusual property as real-world programming languages go.
> You could fix this by, for example, requiring that all symbols
> exported from a module have an explicit type annotation.  Or, if you
> think that's not lazy enough, it could be an error to use an imported
> symbol that doesn't have an explicit type annotation.  You could even
> formalise .hi-boot files if you were truly desperate.

I don't really see this as being any kind of real issue at all. Surely all
GHC needs to do is to concatenate all the modules together, alpha-reduce
the import/export relations and do a compile/type check over the
concatenated module.

> If the Haskell spec requires that multiple modules be analysed
> simultaneously (or multiple times to fixpoint), then that's a bug in
> the spec.  Separate compilation is too important.

Why is it a bug in the spec exactly? And why is separate compilation so


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