[GHC] #10622: Rename Backpack packages to units

[GHC]

#10622: Rename Backpack packages to units
-------------------------------------+-------------------------------------
        Reporter:  ezyang            |                   Owner:  ezyang
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:  backpack
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:  Phab:D1057
-------------------------------------+-------------------------------------

Comment (by simonpj):

 This sounds plausible to me, though as usual with cabal/backpack I am not
 100% sure of my ground.

 I think of it like this:
  * Cabal concerns itself with Cabal packages (units of distribution and
 versioning), including choosing version numbers, downloading them, and
 figuring out if that particular package (instantiated with its transitive
 dependencies) is already installed.

  * GHC concerns itself with Backpack units.

 Both share a single "installed package database".

 But they use it in a different way.  For GHC at least, it's just a cache:
 a place to record the result of previous work (including typechecking
 indefinite packages), so that we don't need to repeat it.  There is no
 harm in repeating it, but it's a waste of time.

 So Cabal need never see the previously-compiled indefinite packages; they
 are just a way for GHC to save time.  Maybe that is what you are saying.

 Another way to attack this is to ask "what questions does Cabal ask the
 installed package database?" and "what questions does GHC ask?".  I think
 the two are different.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10622#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler