[GHC] #2647: Serious typo in IntMap.hs

[Malcolm Wallace]

> Someone has recently (since 6.8.3) taken a "style" pass over  
> `IntMap.hs`.
> Apparently they didn't like reusing identifiers in different scopes,

The reason someone made this change was to eliminate compiler warnings  
with -Wall, and as you rightly point out, the refactoring has  
introduced a new bug where there was no bug before (and there is no  
warning for this new bug).

I think this illustrates the danger of the belief that warnings are  
themselves signs of danger.  Sometimes a warning is simply an  
arbitrary style choice, and it is good practice to ignore it (or  
silence it) rather than change the code.

Regards,
     Malcolm