Re: [Haskell-cafe] why doesn't ghc give you a type signature that works ?

(Re-CC-ing the list) On 18 May 2011 15:16, wrote:

On Wed, 18 May 2011 13:52:46 +1000 Ivan Lazar Miljenovic wrote:

...

What's happening is that the type involves the FFTWReal class. However, this isn't immediately visible to ghci as it isn't in scope, but it can figure out that it's found in Math.FFT.Base.  As such, you need to import that module as well (as opposed to just the Math.FFT class you have already imported).

Well now, that makes perfect sense doesn't it ?

I think my problem is that I think if I import the top-level module then the sub-modules should also be visible, provided I use the full name, or in the case of a qualified name, something link FFT.Base.FFTWReal.

Clearly this is not the case, but why not ?  Is it just the convention that haskell chose, or is there a reason for it ?

Consider Data.ByteString vs Data.ByteString.Lazy; the have the exact same API but for completely different types. Also, it's quite often for package foo to have module Data.Foo, and then module bar extends it with module Data.Foo.Bar; should importing Data.Foo also bring in Data.Foo.Bar? What happens if bar isn't installed? -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com