Aliasing current module qualifier

Herbert Valerio Riedel hvr at
Mon Sep 29 08:19:04 UTC 2014

Hello *,

Here's a situation I've encountered recently, which mades me wish to be
able to define a local alias (in order to avoid CPP use). Consider the
following stupid module:

    module AnnoyinglyLongModuleName
       ( AnnoyinglyLongModuleName.length
       , AnnoyinglyLongModuleName.null
       ) where
    length :: a -> Int
    length _ = 0
    null :: a -> Bool
    null = (== 0) . AnnoyinglyLongModuleName.length

Now it'd be great if I could do the following instead:

    module AnnoyinglyLongModuleName (M.length, M.null) where
    import AnnoyinglyLongModuleName as M -- <- does not work
    length :: a -> Int
    length _ = 0
    null :: a -> Bool
    null = (== 0) . M.length

However, if I try to compile this, GHC complains about

       Bad interface file: AnnoyinglyLongModuleName.hi
           AnnoyinglyLongModuleName.hi: openBinaryFile: does not exist (No such file or directory)

while GHCi tells me:

    Module imports form a cycle:
      module ‘AnnoyinglyLongModuleName’ (AnnoyinglyLongModuleName.hs) imports itself

Is there some other way (without CPP) to create a local alias for the
current module-name? If not, is there a reason GHC couldn't support this
special case of self-aliasing the current module name?

PS: Alternatively, this could be done as a language extension but that'd
    require extending the Haskell grammar:

    module AnnoyinglyLongModuleName as M (M.length, M.null) where


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