[commit: base] master: Implement "TypeLevelReasoning" proposal at wiki:TypeLevelReasoning (365b9d8)

[Simon Peyton-Jones]

Hs-boot files tend to get in the way of optimisation. Moreover, sometimes they are truly necessary, and if there are un-necessary ones that can greatly complicate adding necessary ones.   There are already LOTS of data types declared as instances of Typeable at the place that Typeable class is defined; no harm in one more.

So I'd really prefer the re-jig if that's ok

Simon

|  -----Original Message-----
|  From: Richard Eisenberg [mailto:eir at cis.upenn.edu]
|  Sent: 24 July 2013 22:37
|  To: Simon Peyton-Jones
|  Cc: ghc-devs at haskell.org
|  Subject: Re: [commit: base] master: Implement "TypeLevelReasoning" proposal
|  at wiki:TypeLevelReasoning (365b9d8)
|  
|  I agree that hs-boot files are a little inelegant, but is there a bigger problem with
|  them? I consider instances to be more tied to a datatype definition than the class
|  definition. It may be possible (I think it is) to avoid the Proxy.hs-boot and
|  Equality.hs-boot files if we scatter their instances across the modules. But, then
|  the "definition" of these types would be spread across a large surface area. To me,
|  that makes the types harder to update and perhaps harder to understand (though
|  haddock does a nice job of collecting all the instance declarations together).
|  
|  So, my thought is that the mechanism of hs-boot files may be a little ugly, but it
|  makes the code (that is, the collection of instances) easier to consider as a whole
|  and easier to update. That tradeoff seems worthwhile.
|  
|  That all said, if you (or others) feel strongly about it, I can rejigger it.
|  
|  Richard
|  
|  On Jul 24, 2013, at 3:14 PM, Simon Peyton-Jones wrote:
|  
|  > Richard I am deeply suspicious of all these hs-boot files.
|  >
|  > Instances should preferably go EITHER with the data type declaration OR with
|  the class declaration.
|  >
|  > In the case of Proxy, for example, why can't the Typeable instance for Proxy go
|  in Data.Typeable.Internals?   (And perhaps similarly for other instances.)
|  >
|  > Simon
|  >
|  > |  -----Original Message-----
|  > |  From: ghc-commits [mailto:ghc-commits-bounces at haskell.org] On Behalf Of
|  > |  Richard Eisenberg
|  > |  Sent: 24 July 2013 12:41
|  > |  To: ghc-commits at haskell.org
|  > |  Subject: [commit: base] master: Implement "TypeLevelReasoning" proposal
|  at
|  > |  wiki:TypeLevelReasoning (365b9d8)
|  > |
|  > |  Repository : http://darcs.haskell.org/ghc.git/
|  > |
|  > |  On branch  : master
|  > |
|  > |
|  http://hackage.haskell.org/trac/ghc/changeset/365b9d86d195dc483610a68836b4
|  > |  063656602244
|  > |
|  > |  >---------------------------------------------------------------
|  > |
|  > |  commit 365b9d86d195dc483610a68836b4063656602244
|  > |  Author: Richard Eisenberg <eir at cis.upenn.edu>
|  > |  Date:   Wed Jul 24 12:38:50 2013 +0100
|  > |
|  > |      Implement "TypeLevelReasoning" proposal at wiki:TypeLevelReasoning
|  > |
|  > |      This commit includes a propositional equality (:=:) in Data.Type.Equality,
|  > |      a Proxy type in Data.Proxy, and has updates to Typeable.
|  > |
|  > |      There is an unfortunate number of hs-boot files necessary, but that
|  > |      seems cleaner than moving Typeable instances around willy-nilly.
|  > |
|  > |   Data/Data.hs                   |    2 +-
|  > |   Data/Proxy.hs                  |  129
|  > |  ++++++++++++++++++++++++++++++++++++++++
|  > |   Data/Proxy.hs-boot             |    5 ++
|  > |   Data/Type/Equality.hs          |   99
|  > |  ++++++++++++++++++++++++++++++
|  > |   Data/Type/Equality.hs-boot     |    6 ++
|  > |   Data/Typeable.hs               |   42 +++++++------
|  > |   Data/Typeable/Internal.hs      |    5 +-
|  > |   Data/Typeable/Internal.hs-boot |    3 +-
|  > |   base.cabal                     |    2 +
|  > |   9 files changed, 269 insertions(+), 24 deletions(-)
|  > |
|  > |
|  > |  Diff suppressed because of size. To see it, use:
|  > |
|  > |      git show 365b9d86d195dc483610a68836b4063656602244
|  > |
|  > |  _______________________________________________
|  > |  ghc-commits mailing list
|  > |  ghc-commits at haskell.org
|  > |  http://www.haskell.org/mailman/listinfo/ghc-commits
|  >
|  >
|  >
|