wiki:ImportShadowing

Version 1 (modified by simonpj@…, 6 years ago) (diff)

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Brief explanation

Suppose we have

module M where
      import Data.List
      nub x = x
      foo y = nub y

The program is rejected because the occurrence of nub in foo is ambiguous. This is sometimes tiresome: a new import can force you to add extra M.nub qualifiers.

An obvious alternative is that local declarations shadow imports, so an unqualified name means the locally-defined one. (A warning flag could tell you if you were using this ability.) This is entirely consistent with shadowing in expressions -- except that you can still access at the imported thing with a qualified name.

It's not a big thing, but unless I've missed something, it seems to me that this would make the language more consistent (by treating shadowing consistently), more convenient; and of course it's completely backward compatible.

Proposal

Local declarations shadow imports.

Remarks

This is a modest change. But it is a change, so only worth making if there is significant support (rather than merely absence of opposition).