Adding location information to derived code

Jan Stolarek jan.stolarek at
Wed Jun 10 13:12:19 UTC 2015

Hi devs,

say I have:

  class C a where
    type F a
    type F a = a

  instance C Int

During compilation of "instance C Int" GHC will derive a default associated type instance "F Int = 
Int". That instance has no location information and so any errors that it might cause will have a 
very uninformative source code location 1:1. I want to fix this but I'm not sure whether it is a 
good idea to add location information to automatically generated code. Do we make any assumptions 
that derived code should have no location information?


Politechnika Łódzka
Lodz University of Technology

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