1. 08 Aug, 2006 2 commits
    • simonpj@microsoft.com's avatar
      Fix pre-subsumption and pre-matching · 3098d214
      simonpj@microsoft.com authored
      The pre-subsuption and pre-matching functions should NEVER make bogus
      bindings of type variables, although they are free to bale out and make
      too few bindings.
      
      I hadn't been thiking carefully enough about this, and there were two
      separate bugs.  
      
      - Firstly, in pre-subsumption we must ignore the 'theta'
        part of any overloaded type.  
      
      - Second, in pre-matching, we must return the empty subustition 
        on a mis-match, rather than returning the substitution so far.
      
      This bug showed up when compiling Data.Generics.Schemes.hs, and is
      imortalised in test tc206
      3098d214
    • simonpj@microsoft.com's avatar
      Improve error message · d2b27dcd
      simonpj@microsoft.com authored
      Improve a little-used error message.  Given
      	f :: a -> a
      	f x y = e
      the error says 
      
      	The equations for f have two arguments
      	but its type `a -> a' has only one
      
      (Before, it said "its type `a' has only one" which is bogus.
      d2b27dcd
  2. 10 Jul, 2006 2 commits
  3. 09 Jul, 2006 2 commits
  4. 07 Aug, 2006 2 commits
    • simonpj@microsoft.com's avatar
      Add -fextended-default-rules and -fmono-pat-binds · 6e0c3f50
      simonpj@microsoft.com authored
      Add -fextended-deafult-rules (in response to Don Stewart's message below),
      and document them.
      
      Also doucument -fmono-pat-binds/-fno-mono-pat-binds, which has been in 
      GHC a few weeks now. 
      
      (The two are in one patch because the diffs were so close together
      that Darcs combined them.)
      
      Simon
      
      
      From: Donald Bruce Stewart [mailto:dons@cse.unsw.edu.au] 
      Sent: 07 August 2006 10:52
      
      While we're thinking about defaulting, I have a question..
      
      ghci uses an extended defaulting system, to allow things like:
              Prelude> reverse []
              []
      to work, and to have the right instance of Show found. The manual says:
      
          "..it is tiresome for the user to have to specify the type, so GHCi extends
          Haskell's type-defaulting rules (Section 4.3.4 of the Haskell 98 Report
          (Revised)) as follows. If the expression yields a set of type constraints
          that are all from standard classes (Num, Eq etc.), and at least one is
          either a numeric class or the Show, Eq, or Ord class, GHCi will try to use
          one of the default types, just as described in the Report. The standard
          defaulting rules require that one of the classes is numeric; the difference
          here is that defaulting is also triggered at least one is Show, Eq, or Ord."
      
      Currently, there is no way to get at this "extended" defaulting for compiled
      modules. However, I have a use case for in fact doing this.
      
      With runtime evaluated Haskell, embedding 'interpreters' (over hs-plugins) is
      easy. lambdabot, for example, implements a sandboxed haskell eval system. But
      it doesn't have access to the defaulting mechanism of ghci, so we have:
      
          dons:: > reverse []
          lambdabot:: Add a type signature
          dons:: > reverse [] :: [()]
          lambdabot:: []
      
      Which is annoying -- newbies wonder why they have to add these extra
      constraints to get a Show instance.
      
      I'm wondering, since the extended defaulting mechanisms are already
      implemented, could they be made available to compiled modules as well,
      perhaps using a flag, -fextended-defaulting? 
      6e0c3f50
    • Simon Marlow's avatar
      add a comment · 25adfa02
      Simon Marlow authored
      25adfa02
  5. 04 Aug, 2006 1 commit
    • simonpj@microsoft.com's avatar
      Do pre-subsumption in the main subsumption check · af20907a
      simonpj@microsoft.com authored
      This patch improves the subsumption check (in TcUnify.tc_sub) so that
      it does pre-subsumption first.  The key code is in the case with
      guard (isSigmaTy actual_ty); note the new call to preSubType.
      
      Shorn of details, the question is this.  Should this hold?
      
      	forall a. a->a   <=   Int -> (forall b. Int)
      
      Really, it should; just instantiate 'a' to Int.  This is just what
      the pre-subsumption phase (which used in function applications),
      will do.
      
      I did a bit of refactoring to achieve this.
      
      Fixes Trac #821.  Test tc205 tests.
      af20907a
  6. 01 Aug, 2006 1 commit
    • simonpj@microsoft.com's avatar
      Make unification robust to a boxy type variable meeting itself · 6493f9d3
      simonpj@microsoft.com authored
      Previously, the implicit assumption in unification is that a boxy
      type variable could never occur on both sides of the unification,
      so that we'd never find 
      	bx5 :=: bx5
      
      But the pre-subsumption stuff really means that the same variable
      can occur on both sides.  Consider
      	forall a. a->Int <= bx5->Int
      Then pre-subumption will find a->bx5; and the full subsumption step 
      will find bx5:=bx5.
      
      However, I think there is still no possiblity of a full occurs-check
      failure; that is, 
      	bx5 :=: Tree bx5
      Although I can't quite see how to prove it!  So I've added a
      DEBUG test in uMetaVar to check for this case.
      6493f9d3
  7. 03 Aug, 2006 1 commit
  8. 28 Jul, 2006 3 commits
  9. 27 Jul, 2006 6 commits
  10. 26 Jul, 2006 4 commits
  11. 25 Jul, 2006 5 commits
    • Simon Marlow's avatar
      Unbox the Unique stored in a Name · ddb04482
      Simon Marlow authored
      I measured that this makes the comiler allocate a bit more, but it
      might also make it faster and reduce residency.  The extra allocation
      is probably just because we're not inlining enough somewhere, so I
      think this change is a step in the right direction.
      ddb04482
    • Simon Marlow's avatar
      optimisations to newUnique · bb3dcf39
      Simon Marlow authored
      It turned out that newUnique was wasting one node of the splittable
      uniq supply per invocation: it took the current supply, split it, used
      the unique from one half and stored the other half in the monad.  In
      other words, the unique in the supply stored in the monad was never
      used.  
      
      This optimisation fixes that and adds a bit of strictness, which
      together lead to small reduction in allocations by the compiler, and
      possibly an improvement in residency (hard to tell for sure when GCs
      move around).
      bb3dcf39
    • Simon Marlow's avatar
      tiny bit of extra strictness · 6e2cffab
      Simon Marlow authored
      6e2cffab
    • Simon Marlow's avatar
      Make a SplitUniqSupply contain an Int# rather than an Int · 39a2bccc
      Simon Marlow authored
      The I# constructor is always removed when we make a unique later
      anyway, so this just saves a bit of time and allocation.
      39a2bccc
    • Simon Marlow's avatar
      Generalise Package Support · 61d2625a
      Simon Marlow authored
      This patch pushes through one fundamental change: a module is now
      identified by the pair of its package and module name, whereas
      previously it was identified by its module name alone.  This means
      that now a program can contain multiple modules with the same name, as
      long as they belong to different packages.
      
      This is a language change - the Haskell report says nothing about
      packages, but it is now necessary to understand packages in order to
      understand GHC's module system.  For example, a type T from module M
      in package P is different from a type T from module M in package Q.
      Previously this wasn't an issue because there could only be a single
      module M in the program.
      
      The "module restriction" on combining packages has therefore been
      lifted, and a program can contain multiple versions of the same
      package.
      
      Note that none of the proposed syntax changes have yet been
      implemented, but the architecture is geared towards supporting import
      declarations qualified by package name, and that is probably the next
      step.
      
      It is now necessary to specify the package name when compiling a
      package, using the -package-name flag (which has been un-deprecated).
      Fortunately Cabal still uses -package-name.
      
      Certain packages are "wired in".  Currently the wired-in packages are:
      base, haskell98, template-haskell and rts, and are always referred to
      by these versionless names.  Other packages are referred to with full
      package IDs (eg. "network-1.0").  This is because the compiler needs
      to refer to entities in the wired-in packages, and we didn't want to
      bake the version of these packages into the comiler.  It's conceivable
      that someone might want to upgrade the base package independently of
      GHC.
      
      Internal changes:
      
        - There are two module-related types:
      
              ModuleName      just a FastString, the name of a module
              Module          a pair of a PackageId and ModuleName
      
          A mapping from ModuleName can be a UniqFM, but a mapping from Module
          must be a FiniteMap (we provide it as ModuleEnv).
      
        - The "HomeModules" type that was passed around the compiler is now
          gone, replaced in most cases by the current package name which is
          contained in DynFlags.  We can tell whether a Module comes from the
          current package by comparing its package name against the current
          package.
      
        - While I was here, I changed PrintUnqual to be a little more useful:
          it now returns the ModuleName that the identifier should be qualified
          with according to the current scope, rather than its original
          module.  Also, PrintUnqual tells whether to qualify module names with
          package names (currently unused).
      
      Docs to follow.
      61d2625a
  12. 06 Jul, 2006 2 commits
  13. 04 Jul, 2006 7 commits
  14. 24 Jul, 2006 1 commit
  15. 22 Jul, 2006 1 commit
    • simonpj@microsoft.com's avatar
      Add -fmono-pat-binds, and make it the default · 10ffe4f7
      simonpj@microsoft.com authored
      In Haskell 98, pattern bindings are generalised.  Thus in
      	(f,g) = (\x->x, \y->y)
      both f and g will get polymorphic types.  I have become convinced
      that generalisation for pattern-bound variables is just a bridge
      toof far. It is (I claim) almost never needed, and it adds significant
      complication.  (All the more so if we add bang patterns.)
      
      So the flag -fmono-pat-binds switches off generalisation for pattern
      bindings.  (A single variable is treated as a degnerate funtction
      binding.)  
      
      Furthremore, as an experiment, I'm making it the default.  I want
      to see how many progarms fail with monomorphic pattern bindings.
      
      You can recover the standard behaviour with -fno-mono-pa-binds.
      10ffe4f7