The "INLINABLE" pragma's name is misleading, it is more like "SPECIALISABLE". Consider the documentation for INLINABLE:

Top-level definitions can be marked INLINABLE.

myComplicatedFunction :: (Show a, Num a) => ...
myComplicatedFunction = ...

{-# INLINABLE myComplicatedFunction #-}

This causes exactly two things to happens.

  1. The function's (exact) definition is included in the interface file for the module.
  2. The function will be specialised at use sites -- even across modules.

Note that GHC is no more keen to inline an INLINABLE function than any other.

I propose that we deprecate "INLINABLE" over a number of years at the same time as introducing "SPECIALISABLE". This wouldn't cause breakages for a long time.