Changes between Version 3 and Version 4 of Commentary/Packages/MultiInstances


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Timestamp:
Mar 22, 2012 2:13:58 PM (2 years ago)
Author:
simonmar
Comment:

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  • Commentary/Packages/MultiInstances

    v3 v4  
    1212 
    1313 * GHC: discard conflicting instances during its shadowing phase 
     14   ** SDM: GHC will currently do *something* here, but it might end up with a result that the user didn't want/expect.  One way to improve things is to prioritise packages that were installed more recently. 
     15   ** Andres suggests that GHC should be much cleverer, and look at the actual dependencies of the modules being compiled before deciding which packages to enable.  This would almost certainly result in more things working and possibly less surprising behaviour sometimes, but Simon thinks that (a) it is too hard, (b) if users need this, they should use Cabal and its dependency resolver, which will do a good job, (c) you can often resolve problems by adding `-package X`, and (d) eventually we will want a system where users manage separate sessions, so they can set up an environment in which the packages they want are available.  This has a lot in common with `cabal-dev` and sandboxes, so the mechanisms (and concepts) should be shared. 
    1416 
    1517 * GHC: allow specifying a package instance in the -package flags 
     18   ** SDM: already done 
    1619 
    1720 * instances of packages must install in a different location 
    1821   * install directory includes hash? 
     22   * SDM: not done yet.  One problem is that we don't know the hash until the package is built, but we need to know the install locations earlier because we bake them into `Paths_foo.hs`. 
    1923 
    2024 * ghc-pkg cleanup: remove old/unused instances of packages 
    2125   * how can we tell when something is unnecessary? 
     26 
     27== Next step: dealing with ways == 
    2228 
    2329 * Add the "way" to InstalledPackageInfo, include the way in the hash