But what should the following kind of report translate to?
Error when renaming:: Constructor OK used at 117:30, 103:15, 98:21, 72:13, 35:5 is not defined. Identifier splitWhile used at 110:13, 106:8, 102:8, 91:13 is not defined. Identifier digit used at 272:52, 259:52 is not defined.
Do you want a separate line for each?
IMHO something like the following would be close to perfect: Error when renaming:: file.hs:35:5: Constructor OK is not defined (4 other uses) file.hs:91:13: Identifier splitWhile is not defined (3 other uses) file.hs:259:52: Identifier digit is not defined (1 other use) etc. This allows one to automatically get to the _first_ occurrence. Once the editor's cursor is there, the locations of the rest can be discovered by searching, if one really wants to see them (one often doesn't). With a really fast compiler one often saves time by making one fix and trying again, rather than by deciphering and using information from very involved diagnostics.
And how about this one:
Error after type deriving/checking: Type error type clash between Prelude.Int and Main.Foo when trying to apply function at 4:17 to its 1:st argument at 4:8.
How about: file1.hs:4:8: Error after type deriving/checking: Type error type clash between Prelude.Int and Main.Foo when trying to apply function to its 1:st argument file2.hs:4:17: (the function is defined here). This would allow one to make Emacs put the cursor first in the offending place, and then - if one wishes - at the definition. Regards, -- Feliks