1. 25 Feb, 2005 1 commit
  2. 18 Jan, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-01-18 12:18:11 by simonpj] · ac80e0de
      simonpj authored
      ------------------------
          Reorganisation of hi-boot files
        	------------------------
      
      The main point of this commit is to arrange that in the Compilation
      Manager's dependendency graph, hi-boot files are proper nodes. This
      is important to make sure that we compile everything in the right
      order.  It's a step towards hs-boot files.
      
      * The fundamental change is that CompManager.ModSummary has a new
        field, ms_boot :: IsBootInterface
      
        I also tided up CompManager a bit.  No change to the Basic Plan.
      
        ModSummary is now exported abstractly from CompManager (was concrete)
      
      * Hi-boot files now have import declarations.  The idea is they are
        compulsory, so that the dependency analyser can find them
      
      * I changed an invariant: the Compilation Manager used to ensure that
        hscMain was given a HomePackageTable only for the modules 'below' the
        one being compiled.  This was really only important for instances and
        rules, and it was a bit inconvenient.  So I moved the filter to the
        compiler itself: see HscTypes.hptInstances and hptRules.
      
      * Module Packages.hs now defines
          data PackageIdH
          = HomePackage 		-- The "home" package is the package
       				-- curently being compiled
          | ExtPackage PackageId	-- An "external" package is any other package
      
         It was just a Maybe type before, so this makes it a bit clearer.
      
      * I tried to add a bit better location info to the IfM monad, so that
        errors in interfaces come with a slightly more helpful error message.
        See the if_loc field in TcRnTypes --- and follow-on consequences
      
      * Changed Either to Maybes.MaybeErr in a couple of places (more perspicuous)
      ac80e0de
  3. 27 Dec, 2004 1 commit
  4. 24 Dec, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-12-24 16:14:36 by simonpj] · 339d5220
      simonpj authored
      ---------------------------
                Refactor the simplifier
        	---------------------------
      
      Driven by a GADT bug, I have refactored the simpifier, and the way GHC
      treats substitutions.  I hope I have gotten it right.  Be cautious about updating.
      
      * coreSyn/Subst.lhs has gone
      
      * coreSyn/CoreSubst replaces it, except that it's quite a bit simpler
      
      * simplCore/SimplEnv is added, and contains the simplifier-specific substitution
        stuff
      
      Previously Subst was trying to be all things to all men, and that was making
      it Too Complicated.
      
      There may be a little more code now, but it's much easier to understand.
      339d5220
  5. 26 Nov, 2004 1 commit
    • simonmar's avatar
      [project @ 2004-11-26 16:19:45 by simonmar] · ef5b4b14
      simonmar authored
      Further integration with the new package story.  GHC now supports
      pretty much everything in the package proposal.
      
        - GHC now works in terms of PackageIds (<pkg>-<version>) rather than
          just package names.  You can still specify package names without
          versions on the command line, as long as the name is unambiguous.
      
        - GHC understands hidden/exposed modules in a package, and will refuse
          to import a hidden module.  Also, the hidden/eposed status of packages
          is taken into account.
      
        - I had to remove the old package syntax from ghc-pkg, backwards
          compatibility isn't really practical.
      
        - All the package.conf.in files have been rewritten in the new syntax,
          and contain a complete list of modules in the package.  I've set all
          the versions to 1.0 for now - please check your package(s) and fix the
          version number & other info appropriately.
      
        - New options:
      
      	-hide-package P    sets the expose flag on package P to False
      	-ignore-package P  unregisters P for this compilation
      
      	For comparison, -package P sets the expose flag on package P
              to True, and also causes P to be linked in eagerly.
      
              -package-name is no longer officially supported.  Unofficially, it's
      	a synonym for -ignore-package, which has more or less the same effect
      	as -package-name used to.
      
      	Note that a package may be hidden and yet still be linked into
      	the program, by virtue of being a dependency of some other package.
      	To completely remove a package from the compiler's internal database,
              use -ignore-package.
      
      	The compiler will complain if any two packages in the
              transitive closure of exposed packages contain the same
              module.
      
      	You *must* use -ignore-package P when compiling modules for
              package P, if package P (or an older version of P) is already
              registered.  The compiler will helpfully complain if you don't.
      	The fptools build system does this.
      
         - Note: the Cabal library won't work yet.  It still thinks GHC uses
           the old package config syntax.
      
      Internal changes/cleanups:
      
         - The ModuleName type has gone away.  Modules are now just (a
           newtype of) FastStrings, and don't contain any package information.
           All the package-related knowledge is in DynFlags, which is passed
           down to where it is needed.
      
         - DynFlags manipulation has been cleaned up somewhat: there are no
           global variables holding DynFlags any more, instead the DynFlags
           are passed around properly.
      
         - There are a few less global variables in GHC.  Lots more are
           scheduled for removal.
      
         - -i is now a dynamic flag, as are all the package-related flags (but
           using them in {-# OPTIONS #-} is Officially Not Recommended).
      
         - make -j now appears to work under fptools/libraries/.  Probably
           wouldn't take much to get it working for a whole build.
      ef5b4b14
  6. 25 Nov, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-11-25 11:36:34 by simonpj] · 1f7da302
      simonpj authored
      ------------------------------------------
      	Keep-alive set and Template Haskell quotes
      	------------------------------------------
      
      a) Template Haskell quotes should be able to mention top-leve
         things without resorting to lifting.  Example
      
      	module Foo( foo ) where
      	  f x = x
      	  foo = [| f 4 |]
      
         Here the reference to 'f' is ok; no need to 'lift' it.
         The relevant changes are in TcExpr.tcId
      
      b) However, we must take care not to discard the binding for f,
         so we add it to the 'keep-alive' set for the module.  I've
         now made this into (another) mutable bucket, tcg_keep, 
         in the TcGblEnv
      
      c) That in turn led me to look at the handling of orphan rules;
         as a result I made IdCoreRule into its own data type, which
         has simle but non-local ramifications
      1f7da302
  7. 30 Sep, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-09-30 10:35:15 by simonpj] · 23f40f0e
      simonpj authored
      ------------------------------------
      	Add Generalised Algebraic Data Types
      	------------------------------------
      
      This rather big commit adds support for GADTs.  For example,
      
          data Term a where
       	  Lit :: Int -> Term Int
      	  App :: Term (a->b) -> Term a -> Term b
      	  If  :: Term Bool -> Term a -> Term a
      	  ..etc..
      
          eval :: Term a -> a
          eval (Lit i) = i
          eval (App a b) = eval a (eval b)
          eval (If p q r) | eval p    = eval q
          		    | otherwise = eval r
      
      
      Lots and lots of of related changes throughout the compiler to make
      this fit nicely.
      
      One important change, only loosely related to GADTs, is that skolem
      constants in the typechecker are genuinely immutable and constant, so
      we often get better error messages from the type checker.  See
      TcType.TcTyVarDetails.
      
      There's a new module types/Unify.lhs, which has purely-functional
      unification and matching for Type. This is used both in the typechecker
      (for type refinement of GADTs) and in Core Lint (also for type refinement).
      23f40f0e
  8. 21 Apr, 2004 2 commits
    • simonpj's avatar
      [project @ 2004-04-21 12:45:54 by simonpj] · 711ede5f
      simonpj authored
      Do a much better job of slurping RULES.  
      
      Now that stuff is slurped in lazily, as the simplifier pokes on it,
      we may not get the rules as early as we might wish.  In the current
      HEAD, no new rules are slurped in after the beginning of SimplCore,
      and that means we permanently miss many rules.
      
      This commit arranges that every time round the simplifier loop we
      slurp in any new rules, and put them into the in-scope set, where the
      simplifier can find them.
      
      It's still possible that a rule might be slurped in a little later than
      in earlier versions of GHC, leading to more simplifier iterations,
      but let's see if that turns out to be a problem in practice.
      711ede5f
    • simonpj's avatar
      [project @ 2004-04-21 12:36:24 by simonpj] · e791a226
      simonpj authored
      Comments only
      e791a226
  9. 02 Apr, 2004 1 commit
  10. 30 Dec, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-12-30 16:29:17 by simonpj] · f714e6b6
      simonpj authored
      ----------------------------
              Re-do kind inference (again)
      	----------------------------
      
         [WARNING: interface file binary representation has
         (as usual) changed slightly; recompile your libraries!]
      
      Inspired by the lambda-cube, for some time GHC has used
      	type Kind = Type
      That is, kinds were represented by the same data type as types.
      
      But GHC also supports unboxed types and unboxed tuples, and these
      complicate the kind system by requiring a sub-kind relationship.
      Notably, an unboxed tuple is acceptable as the *result* of a
      function but not as an *argument*.  So we have the following setup:
      
      		 ?
      		/ \
      	       /   \
      	      ??   (#)
      	     /  \
                  *   #
      
      where	*    [LiftedTypeKind]   means a lifted type
      	#    [UnliftedTypeKind] means an unlifted type
      	(#)  [UbxTupleKind]     means unboxed tuple
      	??   [ArgTypeKind]      is the lub of *,#
      	?    [OpenTypeKind]	means any type at all
      
      In particular:
      
        error :: forall a:?. String -> a
        (->)  :: ?? -> ? -> *
        (\(x::t) -> ...)	Here t::?? (i.e. not unboxed tuple)
      
      All this has beome rather difficult to accommodate with Kind=Type, so this
      commit splits the two.
      
        * Kind is a distinct type, defined in types/Kind.lhs
      
        * IfaceType.IfaceKind disappears: we just re-use Kind.Kind
      
        * TcUnify.unifyKind is a distinct unifier for kinds
      
        * TyCon no longer needs KindCon and SuperKindCon variants
      
        * TcUnify.zapExpectedType takes an expected Kind now, so that
          in TcPat.tcMonoPatBndr we can express that the bound variable
          must have an argTypeKind (??).
      
      The big change is really that kind inference is much more systematic and
      well behaved.  In particular, a kind variable can unify only with a
      "simple kind", which is built from * and (->).  This deals neatly
      with awkward questions about how we can combine sub-kinding with type
      inference.
      
      Lots of small consequential changes, especially to the kind-checking
      plumbing in TcTyClsDecls.  (We played a bit fast and loose before, and
      now we have to be more honest, in particular about how kind inference
      works for type synonyms.  They can have kinds like (* -> #), so
      
      This cures two long-standing SourceForge bugs
      
      * 753777 (tcfail115.hs), which used erroneously to pass,
        but crashed in the code generator
            type T a = Int -> (# Int, Int #)
            f :: T a -> T a
            f t = \x -> case t x of r -> r
      
      * 753780 (tc167.hs), which used erroneously to fail
            f :: (->) Int# Int#
      
      
      Still, the result is not entirely satisfactory.  In particular
      
      * The error message from tcfail115 is pretty obscure
      
      * SourceForge bug 807249 (Instance match failure on openTypeKind)
        is not fixed.  Alas.
      f714e6b6
  11. 29 Oct, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-10-29 18:14:27 by simonpj] · 7c3d4a1f
      simonpj authored
      Fix a bad consequence of the new story for the generic toT/fromT functions
      derived from data types declarations. The problem was that they were being
      generated and then discarded by the simplifier, because there was nothing
      keeping them alive.
      
      This commit
        * Adds a field tcg_keep to the TcGblEnv, which records things
          to be kept alive;
      
        * Makes the desugarer pin the keep-alive flag on each binding
          (it's actually a call to setIdLocalExported)
      
        * Removes that job from updateBinders in SimplCore
      
      
      It's somewhat tiresome, but not really difficult.
      7c3d4a1f
  12. 13 Oct, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-10-13 10:43:02 by simonpj] · 7e7c11b2
      simonpj authored
      Deal corectly with rules for Ids defined in this module,
      even when they are imported (as orphans) from other modules.
      
      The epicentre for this stuff is SimplCore.
      7e7c11b2
  13. 10 Oct, 2003 2 commits
  14. 09 Oct, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-10-09 11:58:39 by simonpj] · 98688c6e
      simonpj authored
      -------------------------
      		GHC heart/lung transplant
      		-------------------------
      
      This major commit changes the way that GHC deals with importing
      types and functions defined in other modules, during renaming and
      typechecking.  On the way I've changed or cleaned up numerous other
      things, including many that I probably fail to mention here.
      
      Major benefit: GHC should suck in many fewer interface files when
      compiling (esp with -O).  (You can see this with -ddump-rn-stats.)
      
      It's also some 1500 lines of code shorter than before.
      
      **	So expect bugs!  I can do a 3-stage bootstrap, and run
      **	the test suite, but you may be doing stuff I havn't tested.
      ** 	Don't update if you are relying on a working HEAD.
      
      
      In particular, (a) External Core and (b) GHCi are very little tested.
      
      	But please, please DO test this version!
      
      
      	------------------------
      		Big things
      	------------------------
      
      Interface files, version control, and importing declarations
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      * There is a totally new data type for stuff that lives in interface files:
      	Original names			IfaceType.IfaceExtName
      	Types				IfaceType.IfaceType
      	Declarations (type,class,id)	IfaceSyn.IfaceDecl
      	Unfoldings			IfaceSyn.IfaceExpr
        (Previously we used HsSyn for type/class decls, and UfExpr for unfoldings.)
        The new data types are in iface/IfaceType and iface/IfaceSyn.  They are
        all instances of Binary, so they can be written into interface files.
        Previous engronkulation concering the binary instance of RdrName has
        gone away -- RdrName is not an instance of Binary any more.  Nor does
        Binary.lhs need to know about the ``current module'' which it used to,
        which made it specialised to GHC.
      
        A good feature of this is that the type checker for source code doesn't
        need to worry about the possibility that we might be typechecking interface
        file stuff.  Nor does it need to do renaming; we can typecheck direct from
        IfaceSyn, saving a whole pass (module TcIface)
      
      * Stuff from interface files is sucked in *lazily*, rather than being eagerly
        sucked in by the renamer. Instead, we use unsafeInterleaveIO to capture
        a thunk for the unfolding of an imported function (say).  If that unfolding
        is every pulled on, TcIface will scramble over the unfolding, which may
        in turn pull in the interface files of things mentioned in the unfolding.
      
        The External Package State is held in a mutable variable so that it
        can be side-effected by this lazy-sucking-in process (which may happen
        way later, e.g. when the simplifier runs).   In effect, the EPS is a kind
        of lazy memo table, filled in as we suck things in.  Or you could think
        of it as a global symbol table, populated on demand.
      
      * This lazy sucking is very cool, but it can lead to truly awful bugs. The
        intent is that updates to the symbol table happen atomically, but very bad
        things happen if you read the variable for the table, and then force a
        thunk which updates the table.  Updates can get lost that way. I regret
        this subtlety.
      
        One example of the way it showed up is that the top level of TidyPgm
        (which updates the global name cache) to be much more disciplined about
        those updates, since TidyPgm may itself force thunks which allocate new
        names.
      
      * Version numbering in interface files has changed completely, fixing
        one major bug with ghc --make.  Previously, the version of A.f changed
        only if A.f's type and unfolding was textually different.  That missed
        changes to things that A.f's unfolding mentions; which was fixed by
        eagerly sucking in all of those things, and listing them in the module's
        usage list.  But that didn't work with --make, because they might have
        been already sucked in.
      
        Now, A.f's version changes if anything reachable from A.f (via interface
        files) changes.  A module with unchanged source code needs recompiling
        only if the versions of any of its free variables changes. [This isn't
        quite right for dictionary functions and rules, which aren't mentioned
        explicitly in the source.  There are extensive comments in module MkIface,
        where all version-handling stuff is done.]
      
      * We don't need equality on HsDecls any more (because they aren't used in
        interface files).  Instead we have a specialised equality for IfaceSyn
        (eqIfDecl etc), which uses IfaceEq instead of Bool as its result type.
        See notes in IfaceSyn.
      
      * The horrid bit of the renamer that tried to predict what instance decls
        would be needed has gone entirely.  Instead, the type checker simply
        sucks in whatever instance decls it needs, when it needs them.  Easy!
      
        Similarly, no need for 'implicitModuleFVs' and 'implicitTemplateHaskellFVs'
        etc.  Hooray!
      
      
      Types and type checking
      ~~~~~~~~~~~~~~~~~~~~~~~
      * Kind-checking of types is far far tidier (new module TcHsTypes replaces
        the badly-named TcMonoType).  Strangely, this was one of my
        original goals, because the kind check for types is the Right Place to
        do type splicing, but it just didn't fit there before.
      
      * There's a new representation for newtypes in TypeRep.lhs.  Previously
        they were represented using "SourceTypes" which was a funny compromise.
        Now they have their own constructor in the Type datatype.  SourceType
        has turned back into PredType, which is what it used to be.
      
      * Instance decl overlap checking done lazily.  Consider
      	instance C Int b
      	instance C a Int
        These were rejected before as overlapping, because when seeking
        (C Int Int) one couldn't tell which to use.  But there's no problem when
        seeking (C Bool Int); it can only be the second.
      
        So instead of checking for overlap when adding a new instance declaration,
        we check for overlap when looking up an Inst.  If we find more than one
        matching instance, we see if any of the candidates dominates the others
        (in the sense of being a substitution instance of all the others);
        and only if not do we report an error.
      
      
      
      	------------------------
      	     Medium things
      	------------------------
      
      * The TcRn monad is generalised a bit further.  It's now based on utils/IOEnv.lhs,
        the IO monad with an environment.  The desugarer uses the monad too,
        so that anything it needs can get faulted in nicely.
      
      * Reduce the number of wired-in things; in particular Word and Integer
        are no longer wired in.  The latter required HsLit.HsInteger to get a
        Type argument.  The 'derivable type classes' data types (:+:, :*: etc)
        are not wired in any more either (see stuff about derivable type classes
        below).
      
      * The PersistentComilerState is now held in a mutable variable
        in the HscEnv.  Previously (a) it was passed to and then returned by
        many top-level functions, which was painful; (b) it was invariably
        accompanied by the HscEnv.  This change tidies up top-level plumbing
        without changing anything important.
      
      * Derivable type classes are treated much more like 'deriving' clauses.
        Previously, the Ids for the to/from functions lived inside the TyCon,
        but now the TyCon simply records their existence (with a simple boolean).
        Anyone who wants to use them must look them up in the environment.
      
        This in turn makes it easy to generate the to/from functions (done
        in types/Generics) using HsSyn (like TcGenDeriv for ordinary derivings)
        instead of CoreSyn, which in turn means that (a) we don't have to figure
        out all the type arguments etc; and (b) it'll be type-checked for us.
        Generally, the task of generating the code has become easier, which is
        good for Manuel, who wants to make it more sophisticated.
      
      * A Name now says what its "parent" is. For example, the parent of a data
        constructor is its type constructor; the parent of a class op is its
        class.  This relationship corresponds exactly to the Avail data type;
        there may be other places we can exploit it.  (I made the change so that
        version comparison in interface files would be a bit easier; but in
        fact it tided up other things here and there (see calls to
        Name.nameParent).  For example, the declaration pool, of declararations
        read from interface files, but not yet used, is now keyed only by the 'main'
        name of the declaration, not the subordinate names.
      
      * New types OccEnv and OccSet, with the usual operations.
        OccNames can be efficiently compared, because they have uniques, thanks
        to the hashing implementation of FastStrings.
      
      * The GlobalRdrEnv is now keyed by OccName rather than RdrName.  Not only
        does this halve the size of the env (because we don't need both qualified
        and unqualified versions in the env), but it's also more efficient because
        we can use a UniqFM instead of a FiniteMap.
      
        Consequential changes to Provenance, which has moved to RdrName.
      
      * External Core remains a bit of a hack, as it was before, done with a mixture
        of HsDecls (so that recursiveness and argument variance is still inferred),
        and IfaceExprs (for value declarations).  It's not thoroughly tested.
      
      
      	------------------------
      	     Minor things
      	------------------------
      
      * DataCon fields dcWorkId, dcWrapId combined into a single field
        dcIds, that is explicit about whether the data con is a newtype or not.
        MkId.mkDataConWorkId and mkDataConWrapId are similarly combined into
        MkId.mkDataConIds
      
      * Choosing the boxing strategy is done for *source* type decls only, and
        hence is now in TcTyDecls, not DataCon.
      
      * WiredIn names are distinguished by their n_sort field, not by their location,
        which was rather strange
      
      * Define Maybes.mapCatMaybes :: (a -> Maybe b) -> [a] -> [b]
        and use it here and there
      
      * Much better pretty-printing of interface files (--show-iface)
      
      Many, many other small things.
      
      
      	------------------------
      	     File changes
      	------------------------
      * New iface/ subdirectory
      * Much of RnEnv has moved to iface/IfaceEnv
      * MkIface and BinIface have moved from main/ to iface/
      * types/Variance has been absorbed into typecheck/TcTyDecls
      * RnHiFiles and RnIfaces have vanished entirely.  Their
        work is done by iface/LoadIface
      * hsSyn/HsCore has gone, replaced by iface/IfaceSyn
      * typecheck/TcIfaceSig has gone, replaced by iface/TcIface
      * typecheck/TcMonoType has been renamed to typecheck/TcHsType
      * basicTypes/Var.hi-boot and basicTypes/Generics.hi-boot have gone altogether
      98688c6e
  15. 23 Sep, 2003 1 commit
    • simonmar's avatar
      [project @ 2003-09-23 14:32:57 by simonmar] · abbc5a0b
      simonmar authored
      - Convert many of the optimisation options into dynamic options (that is,
        they can be mentioned in {-# OPTIONS #-} pragmas).
      
      - Add a new way to specify constructor-field unboxing on a selective
        basis.  To tell the compiler to unbox a constructor field, do this:
      
            data T = T !!Int
      
        and GHC will store that field unboxed if possible.  If it isn't possible
        (say, because the field has a sum type) then the annotation is ignored.
      
        The -funbox-strict-fields flag is now a dynamic flag, and has the same
        effect as replacing all the '!' annotations with '!!'.
      abbc5a0b
  16. 02 Jul, 2003 1 commit
  17. 03 Mar, 2003 1 commit
    • simonmar's avatar
      [project @ 2003-03-03 12:43:31 by simonmar] · 19108ede
      simonmar authored
      A round of space-leak fixing.
      
        - re-instate zapping of the PersistentCompilerState at various
          points during the compilation cycle in HscMain.  This affects
          one-shot compilation only, since in this mode the information
          collected in the PCS is not required after creating the final
          interface file.
      
        - Unravel the recursive dependency between MkIface and
          CoreTidy/CoreToStg.  Previously the CafInfo for each binding was
          calculated by CoreToStg, and fed back into the IdInfo of the Ids
          generated by CoreTidy (an earlier pass).  MkIface then took this
          IdInfo and the bindings from CoreTidy to generate the interface;
          but it couldn't do this until *after* CoreToStg, because the CafInfo
          hadn't been calculated yet.  The result was that the CoreTidy
          output lived until after CoreToStg, and at the same time as the
          CorePrep and STG syntax, which is wasted space, not to mention
          the complexity and general ugliness in HscMain.
      
          So now we calculate CafInfo directly in CoreTidy.  The downside is
          that we have to predict what CorePrep is going to do to the
          bindings so we can tell what will turn into a CAF later, but it's
          no worse than before (it turned out that we were doing this
          prediction before in CoreToStg anyhow).
      
        - The typechecker lazilly typechecks unfoldings.  It turns out that
          this is a good idea from a performance perspective, but it also
          means that it must hang on to all the information it needs to
          do the typechecking.  Previously this meant holding on to the
          whole of the typechecker's environment, which includes all sorts
          of stuff which isn't necessary to typecheck unfoldings.  By paring
          down the environment captured by the lazy unfoldings, we can
          save quite a bit of space in the phases after typechecking.
      19108ede
  18. 07 Feb, 2003 1 commit
  19. 04 Feb, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-02-04 15:09:38 by simonpj] · 957bf375
      simonpj authored
      -------------------------------------
      	Remove all vestiges of usage analysis
      	-------------------------------------
      
      This commit removes a large blob of usage-analysis-related code, almost
      all of which was commented out.
      
      Sadly, it doesn't look as if Keith is going to have enough time to polish it
      up, and in any case the actual performance benefits (so far as we can measure
      them) turned out to be pretty modest (a few percent).
      
      So, with regret, I'm chopping it all out.  It's still there in the repository
      if anyone wants go hack on it.  And Tobias Gedell at Chalmers is implementing
      a different analysis, via External Core.
      957bf375
  20. 08 Nov, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-11-08 15:21:27 by simonpj] · 410e4850
      simonpj authored
      --------------------------------
      	Expression simplification for TH
      	--------------------------------
      
      Simplify expressions without any inlining in SimplCore.simplifyExpr.
      
      simplifyExpr is used to simplify a TH splice before running the code,
      and simplifyExpr was using (SimplPhase 0) which allows inlining.
      Unfortunately, when -O is on (which can happen when compiling a program
      with some splices with -O) some inlining can happen which then confuses
      the byte-code generator.  (Unboxed tuples.)
      410e4850
  21. 13 Sep, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-09-13 15:02:25 by simonpj] · 9af77fa4
      simonpj authored
      --------------------------------------
      	Make Template Haskell into the HEAD
      	--------------------------------------
      
      This massive commit transfers to the HEAD all the stuff that
      Simon and Tim have been doing on Template Haskell.  The
      meta-haskell-branch is no more!
      
      WARNING: make sure that you
      
        * Update your links if you are using link trees.
          Some modules have been added, some have gone away.
      
        * Do 'make clean' in all library trees.
          The interface file format has changed, and you can
          get strange panics (sadly) if GHC tries to read old interface files:
          e.g.  ghc-5.05: panic! (the `impossible' happened, GHC version 5.05):
      	  Binary.get(TyClDecl): ForeignType
      
        * You need to recompile the rts too; Linker.c has changed
      
      
      However the libraries are almost unaltered; just a tiny change in
      Base, and to the exports in Prelude.
      
      
      NOTE: so far as TH itself is concerned, expression splices work
      fine, but declaration splices are not complete.
      
      
      		---------------
      		The main change
      		---------------
      
      The main structural change: renaming and typechecking have to be
      interleaved, because we can't rename stuff after a declaration splice
      until after we've typechecked the stuff before (and the splice
      itself).
      
      * Combine the renamer and typecheker monads into one
      	(TcRnMonad, TcRnTypes)
        These two replace TcMonad and RnMonad
      
      * Give them a single 'driver' (TcRnDriver).  This driver
        replaces TcModule.lhs and Rename.lhs
      
      * The haskell-src library package has a module
      	Language/Haskell/THSyntax
        which defines the Haskell data type seen by the TH programmer.
      
      * New modules:
      	hsSyn/Convert.hs 	converts THSyntax -> HsSyn
      	deSugar/DsMeta.hs 	converts HsSyn -> THSyntax
      
      * New module typecheck/TcSplice type-checks Template Haskell splices.
      
      		-------------
      		Linking stuff
      		-------------
      
      * ByteCodeLink has been split into
      	ByteCodeLink	(which links)
      	ByteCodeAsm	(which assembles)
      
      * New module ghci/ObjLink is the object-code linker.
      
      * compMan/CmLink is removed entirely (was out of place)
        Ditto CmTypes (which was tiny)
      
      * Linker.c initialises the linker when it is first used (no need to call
        initLinker any more).  Template Haskell makes it harder to know when
        and whether to initialise the linker.
      
      
      	-------------------------------------
      	Gathering the LIE in the type checker
      	-------------------------------------
      
      * Instead of explicitly gathering constraints in the LIE
      	tcExpr :: RenamedExpr -> TcM (TypecheckedExpr, LIE)
        we now dump the constraints into a mutable varabiable carried
        by the monad, so we get
      	tcExpr :: RenamedExpr -> TcM TypecheckedExpr
      
        Much less clutter in the code, and more efficient too.
        (Originally suggested by Mark Shields.)
      
      
      		-----------------
      		Remove "SysNames"
      		-----------------
      
      Because the renamer and the type checker were entirely separate,
      we had to carry some rather tiresome implicit binders (or "SysNames")
      along inside some of the HsDecl data structures.  They were both
      tiresome and fragile.
      
      Now that the typechecker and renamer are more intimately coupled,
      we can eliminate SysNames (well, mostly... default methods still
      carry something similar).
      
      		-------------
      		Clean up HsPat
      		-------------
      
      One big clean up is this: instead of having two HsPat types (InPat and
      OutPat), they are now combined into one.  This is more consistent with
      the way that HsExpr etc is handled; there are some 'Out' constructors
      for the type checker output.
      
      So:
      	HsPat.InPat	--> HsPat.Pat
      	HsPat.OutPat	--> HsPat.Pat
      	No 'pat' type parameter in HsExpr, HsBinds, etc
      
      	Constructor patterns are nicer now: they use
      		HsPat.HsConDetails
      	for the three cases of constructor patterns:
      		prefix, infix, and record-bindings
      
      	The *same* data type HsConDetails is used in the type
      	declaration of the data type (HsDecls.TyData)
      
      Lots of associated clean-up operations here and there.  Less code.
      Everything is wonderful.
      9af77fa4
  22. 22 Apr, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-04-22 16:06:35 by simonpj] · dbfe93e6
      simonpj authored
      CPR control
      
      1.  Remove -fno-cpr, add -fcpr-off which is a simple static flag
          for switching the new CPR analysis off altogether.
          (The "-fno" machinery is rather complicated.)
      
      2.  Rejig SimplCore a little so that the "old strictness analyser"
          runs both the old strictness analyser and the old CPR analyser,
          which makes it more like the new strictness/CPR analyser.
      
          (How much longer we keep the old strictness/CPR analyser in the
          compiler at all I don't know.  It's just for comparision purposes
          when we write the paper.)
      dbfe93e6
  23. 15 Mar, 2002 1 commit
  24. 11 Feb, 2002 1 commit
    • chak's avatar
      [project @ 2002-02-11 08:20:38 by chak] · 10fcd78c
      chak authored
      *******************************
      		       * Merging from ghc-ndp-branch *
      		       *******************************
      
      This commit merges the current state of the "parallel array extension" and
      includes the following:
      
      * (Almost) completed Milestone 1:
        - The option `-fparr' activates the H98 extension for parallel arrays.
        - These changes have a high likelihood of conflicting (in the CVS sense)
          with other changes to GHC and are the reason for merging now.
        - ToDo: There are still some (less often used) functions not implemented in
      	  `PrelPArr' and a mechanism is needed to automatically import
      	  `PrelPArr' iff `-fparr' is given.  Documentation that should go into
      	  the Commentary is currently in `ghc/compiler/ndpFlatten/TODO'.
      
      * Partial Milestone 2:
        - The option `-fflatten' activates the flattening transformation and `-ndp'
          selects the "ndp" way (where all libraries have to be compiled with
          flattening).  The way option `-ndp' automagically turns on `-fparr' and
          `-fflatten'.
        - Almost all changes are in the new directory `ndpFlatten' and shouldn't
          affect the rest of the compiler.  The only exception are the options and
          the points in `HscMain' where the flattening phase is called when
          `-fflatten' is given.
        - This isn't usable yet, but already implements function lifting,
          vectorisation, and a new analysis that determines which parts of a module
          have to undergo the flattening transformation.  Missing are data structure
          and function specialisation, the unboxed array library (including fusion
          rules), and lots of testing.
      
      I have just run the regression tests on the thing without any problems.  So,
      it seems, as if we haven't broken anything crucial.
      10fcd78c
  25. 05 Feb, 2002 1 commit
  26. 10 Dec, 2001 1 commit
    • simonmar's avatar
      [project @ 2001-12-10 14:07:30 by simonmar] · 973539a8
      simonmar authored
      Make the inclusion of the old strictness analyser, CPR analyser, and
      the relevant IdInfo components, conditional on DEBUG.  This makes
      IdInfo smaller by three fields in a non-DEBUG compiler, and reduces
      the risk that the unused fields could harbour space leaks.
      
      Eventually these passes will go away altogether.
      973539a8
  27. 18 Oct, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-10-18 16:29:12 by simonpj] · 685e04e4
      simonpj authored
      ----------------------------------------------
      	The CoreTidy/CorePrep/CoreToStg saga continues
      	[actually, this commit mostly completes the job]
      	----------------------------------------------
      
      			DO NOT MERGE!
      
      * CorePrep injects implicit bindings, not the type checker,
        nor CgConTbls.   (This way, all the code generators see
        them, so no need to fiddle with the byte code generator.)
      
        As a result, all bindings in the module are for LocalIds,
        at least until CoreTidy.   This is a Big Win.
      
        Hence remove nasty isImplicitId test in update_bndr in
        SimplCore and DmdAnal
      
      * hasNoBinding is no longer true of a dataConId (worker).
        There's an implicit curried binding for it.
      
      * Remove yukky test in exprIsTrivial that did not regard
        a hasNoBinding Id as trivial; similarly in SimplUtils.tryEtaReduce
      
      * In CoreTidy, get the names to avoid from the type env.
        That way it includes implicit bindings too.
      
      * CoreTidy set the Arity of a top-level Id permanently;
        it's up to the rest of the compiler to respect it.
        Notably, CorePrep uses etaExpand to make the manifest arity
        match the claimed arity.
      
      * As a result, nuke CgArity, so that CgInfo now contains only
        CafInfo.  The CafInfo is knot-tied as before.
      
      
      Other things
      
      * In Simplify.simplLazyBind, be a bit keener to float bindings
        out if it's a top-level binding.
      685e04e4
  28. 01 Oct, 2001 1 commit
  29. 26 Sep, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-09-26 16:19:28 by simonpj] · 6858f7c1
      simonpj authored
      ------------------
      		Simon's big commit
      		------------------
      	[ These files seem to have been left out for some reason ]
      
      
      This commit, which I don't think I can sensibly do piecemeal, consists
      of the things I've been doing recently, mainly directed at making
      Manuel, George, and Marcin happier with RULES.
      
      
      Reogranise the simplifier
      ~~~~~~~~~~~~~~~~~~~~~~~~~
      1. The simplifier's environment is now an explicit parameter.  This
      makes it a bit easier to figure out where it is going.
      
      2. Constructor arguments can now be arbitrary expressions, except
      when the application is the RHS of a let(rec).  This makes it much
      easier to match rules like
      
      	RULES
      	    "foo"  f (h x, g y) = f' x y
      
      In the simplifier, it's Simplify.mkAtomicArgs that ANF-ises a
      constructor application where necessary.  In the occurrence analyser,
      there's a new piece of context info (OccEncl) to say whether a
      constructor app is in a place where it should be in ANF.  (Unless
      it knows this it'll give occurrence info which will inline the
      argument back into the constructor app.)
      
      3. I'm experimenting with doing the "float-past big lambda" transformation
      in the full laziness pass, rather than mixed in with the simplifier (was
      tryRhsTyLam).
      
      4.  Arrange that
      	case (coerce (S,T) (x,y)) of ...
      will simplify.  Previous it didn't.
      A local change to CoreUtils.exprIsConApp_maybe.
      
      5. Do a better job in CoreUtils.exprEtaExpandArity when there's an
      error function in one branch.
      
      
      Phase numbers, RULES, and INLINE pragmas
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      1.  Phase numbers decrease from N towards zero (instead of increasing).
      This makes it easier to add new earlier phases, which is what users want
      to do.
      
      2.  RULES get their own phase number, N, and are disabled in phases before N.
      
      e.g. 	{-# RULES "foo" [2] forall x y.  f (x,y) = f' x y #-}
      
      Note the [2], which says "only active in phase 2 and later".
      
      3.  INLINE and NOINLINE pragmas have a phase number to.  This is now treated
      in just the same way as the phase number on RULE; that is, the Id is not inlined
      in phases earlier than N.  In phase N and later the Id *may* be inlined, and
      here is where INLINE and NOINLINE differ: INLNE makes the RHS look small, so
      as soon as it *may* be inlined it probably *will* be inlined.
      
      The syntax of the phase number on an INLINE/NOINLINE pragma has changed to be
      like the RULES case (i.e. in square brackets).  This should also make sure
      you examine all such phase numbers; many will need to change now the numbering
      is reversed.
      
      Inlining Ids is no longer affected at all by whether the Id appears on the
      LHS of a rule.  Now it's up to the programmer to put a suitable INLINE/NOINLINE
      pragma to stop it being inlined too early.
      
      
      Implementation notes:
      
      *  A new data type, BasicTypes.Activation says when a rule or inline pragma
      is active.   Functions isAlwaysActive, isNeverActive, isActive, do the
      obvious thing (all in BasicTypes).
      
      * Slight change in the SimplifierSwitch data type, which led to a lot of
      simplifier-specific code moving from CmdLineOpts to SimplMonad; a Good Thing.
      
      * The InlinePragma in the IdInfo of an Id is now simply an Activation saying
      when the Id can be inlined.  (It used to be a rather bizarre pair of a
      Bool and a (Maybe Phase), so this is much much easier to understand.)
      
      * The simplifier has a "mode" environment switch, replacing the old
      black list.  Unfortunately the data type decl has to be in
      CmdLineOpts, because it's an argument to the CoreDoSimplify switch
      
          data SimplifierMode = SimplGently | SimplPhase Int
      
      Here "gently" means "no rules, no inlining".   All the crucial
      inlining decisions are now collected together in SimplMonad
      (preInlineUnconditionally, postInlineUnconditionally, activeInline,
      activeRule).
      
      
      Specialisation
      ~~~~~~~~~~~~~~
      1.  Only dictionary *functions* are made INLINE, not dictionaries that
      have no parameters.  (This inline-dictionary-function thing is Marcin's
      idea and I'm still not sure whether it's a good idea.  But it's definitely
      a Bad Idea when there are no arguments.)
      
      2.  Be prepared to specialise an INLINE function: an easy fix in
      Specialise.lhs
      
      But there is still a problem, which is that the INLINE wins
      at the call site, so we don't use the specialised version anyway.
      I'm still unsure whether it makes sense to SPECIALISE something
      you want to INLINE.
      
      
      
      
      
      Random smaller things
      ~~~~~~~~~~~~~~~~~~~~~~
      
      * builtinRules (there was only one, but may be more) in PrelRules are now
        incorporated.   They were being ignored before...
      
      * OrdList.foldOL -->  OrdList.foldrOL, OrdList.foldlOL
      
      * Some tidying up of the tidyOpenTyVar, tidyTyVar functions.  I've
        forgotten exactly what!
      6858f7c1
  30. 14 Sep, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-09-14 15:51:41 by simonpj] · 5ab261bb
      simonpj authored
      --------------------------
      	Add a rule-check pass
      	(special request by Manuel)
      	--------------------------
      
      	DO NOT merge with stable
      
      The flag
      
      	-frule-check foo
      
      will report all sites at which RULES whose name starts with "foo.."
      might apply, but in fact the arguments don't match so the rule
      doesn't apply.
      
      The pass is run right after all the core-to-core passes.  (Next thing
      to do: make the core-to-core script external, so you can fiddle with
      it.  Meanwhile, the core-to-core script is in
      	DriverState.builCoreToDo
      so you can move the CoreDoRuleCheck line around if you want.
      
      The format of the report is experimental: Manuel, feel free to fiddle
      with it.
      
      Most of the code is in specialise/Rules.lhs
      
      
      Incidental changes
      ~~~~~~~~~~~~~~~~~~
      Change BuiltinRule so that the rule name is accessible
      without actually successfully applying the rule.  This
      change affects quite a few files in a trivial way.
      5ab261bb
  31. 07 Sep, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-09-07 12:44:30 by simonpj] · 991a868b
      simonpj authored
      ----------------------------------------
      	Make dict funs and default methods
      	into LocalIds only at their binding site
      	----------------------------------------
              [part of 3 related commits]
      
      There's a long comment about this with MkId.mkDefaultMethodId,
      which I reproduce below.
      
      While I was at it, I renamed setIdNoDiscard to setIdLocalExported.
      Which is hardly an improvement, I'm afraid.  This renaming touches
      	Var.lhs, Id.lhs, SimplCore.lhs
      in a trivial way.
      
      	---------------------
      
      Dict funs and default methods are *not* ImplicitIds.  Their definition
      involves user-written code, so we can't figure out their strictness etc
      based on fixed info, as we can for constructors and record selectors (say).
      
      We build them as GlobalIds, but when in the module where they are
      bound, we turn the Id at the *binding site* into an exported LocalId.
      This ensures that they are taken to account by free-variable finding
      and dependency analysis (e.g. CoreFVs.exprFreeVars).   The simplifier
      will propagate the LocalId to all occurrence sites.
      
      Why shouldn't they be bound as GlobalIds?  Because, in particular, if
      they are globals, the specialiser floats dict uses above their defns,
      which prevents good simplifications happening.  Also the strictness
      analyser treats a occurrence of a GlobalId as imported and assumes it
      contains strictness in its IdInfo, which isn't true if the thing is
      bound in the same module as the occurrence.
      
      It's OK for dfuns to be LocalIds, because we form the instance-env to
      pass on to the next module (md_insts) in CoreTidy, afer tidying
      and globalising the top-level Ids.
      
      BUT make sure they are *exported* LocalIds (setIdLocalExported) so
      that they aren't discarded by the occurrence analyser.
      991a868b
  32. 17 Jul, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-07-17 15:28:30 by simonpj] · fdc83001
      simonpj authored
      --------------------------------
      	First cut at the demand analyser
      	--------------------------------
      
      This demand analyser is intended to replace the strictness/absence
      analyser, and the CPR analyser.
      
      This commit adds it to the compiler, but in an entirely non-invasive
      way.
      
      	If you build the compiler without -DDEBUG,
      	you won't get it at all.
      
      	If you build the compiler with -DDEBUG,
      	you'll get the demand analyser, but the existing
      	strictness analyser etc are still there.  All the
      	demand analyser does is to compare its output with
      	the existing stuff and report differences.
      
      There's no cross-module stuff for demand info yet.
      
      The strictness/demand info is put the IdInfo as
      	newStrictnessInfo
      	newDemandInfo
      
      Eventually we'll remove the old ones.
      
      Simon
      fdc83001
  33. 09 May, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-05-09 13:28:11 by simonpj] · f11dacd8
      simonpj authored
      ****	MERGE WITH 5.00 BRANCH     ********
      
      	-------------------------------
      	Fix a rather obscure rule bogon
      	-------------------------------
      
      The problem was that there was
      
      	class Foo a where
      	  op :: a -> a
      
      	{-# RULES "op" op x = x #-}
      
      or something like that.  We attach locally defined rules, like this one,
      to the local binding, in SimplCore.prepareRules.  Alas op doesn't reply
      "True" to isLocalId, because it's a class selector (so it's a GlobalId
      throughout).   Result: we treated the rule as an imported rule, and
      therefore gave 'op' a fresh unique (becuase it looked as if it was
      already in scope).  This only blew up in ghc --make or --interactive.
      
      The handling of local vs global rules is rather unsatisfactory.
      Something to muse on.
      f11dacd8
  34. 13 Mar, 2001 1 commit
    • simonmar's avatar
      [project @ 2001-03-13 12:50:29 by simonmar] · 10cbc75d
      simonmar authored
      Some rearrangements that Simon & I have been working on recently:
      
          - CoreSat is now CorePrep, and is a general "prepare-for-code-
            generation" pass.  It does cloning, saturation of constructors &
            primops, A-normal form, and a couple of other minor fiddlings.
      
          - CoreTidy no longer does cloning, and minor fiddlings.  It doesn't
            need the unique supply any more, so that's removed.
      
          - CoreToStg now collects CafInfo and the list of CafRefs for each
            binding.  The SRT pass is much simpler now.
      
          - IdInfo now has a CgInfo field for "code generator info".  It currently
            contains arity (the actual code gen arity which affects the calling
            convention as opposed to the ArityInfo which is a measure of how
            many arguments the Id can be applied to before it does any work), and
            CafInfo.
      
            Previously we overloaded the ArityInfo field to contain both
            codegen arity and simplifier arity.  Things are cleaner now.
      
          - CgInfo is collected by CoreToStg, and passed back into CoreTidy in
            a loop.  The compiler will complain rather than going into a black
            hole if the CgInfo is pulled on too early.
      
          - Worker info in an interface file now comes with arity info attached.
            Previously the main arity info was overloaded for this purpose, but
            it lead to a few hacks in the compiler, this tidies things up somewhat.
      
      Bottom line: we removed several fragilities, and tidied up a number of
      things.  Code size should be smaller, but we'll see...
      10cbc75d
  35. 08 Mar, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-03-08 12:07:38 by simonpj] · 51a571c0
      simonpj authored
      --------------------
      	A major hygiene pass
      	--------------------
      
      1. The main change here is to
      
      	Move what was the "IdFlavour" out of IdInfo,
      	and into the varDetails field of a Var
      
         It was a mess before, because the flavour was a permanent attribute
         of an Id, whereas the rest of the IdInfo was ephemeral.  It's
         all much tidier now.
      
         Main places to look:
      
      	   Var.lhs	Defn of VarDetails
      	   IdInfo.lhs	Defn of GlobalIdDetails
      
         The main remaining infelicity is that SpecPragmaIds are right down
         in Var.lhs, which seems unduly built-in for such an ephemeral thing.
         But that is no worse than before.
      
      
      2. Tidy up the HscMain story a little.  Move mkModDetails from MkIface
         into CoreTidy (where it belongs more nicely)
      
         This was partly forced by (1) above, because I didn't want to make
         DictFun Ids into a separate kind of Id (which is how it was before).
         Not having them separate means we have to keep a list of them right
         through, rather than pull them out of the bindings at the end.
      
      3. Add NameEnv as a separate module (to join NameSet).
      
      4. Remove unnecessary {-# SOURCE #-} imports from FieldLabel.
      51a571c0
  36. 05 Mar, 2001 1 commit
  37. 28 Feb, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-02-28 11:48:34 by simonpj] · 12e6a9a5
      simonpj authored
      Add most of the code for constructor specialisation.  The comment
      below is reproduced from specialise/SpecConstr.lhs.
      
      It doesn't quite work properly yet, because we need to have 
      rules in scope in a recursive function's own RHS, and that
      entails a bit of fiddling I havn't yet completed.  But SpecConstr
      itself is a nice neat 250 lines of code.
      
      -----------------------------------------------------
      			Game plan
      -----------------------------------------------------
      
      Consider
      	drop n []     = []
      	drop 0 xs     = []
      	drop n (x:xs) = drop (n-1) xs
      
      After the first time round, we could pass n unboxed.  This happens in
      numerical code too.  Here's what it looks like in Core:
      
      	drop n xs = case xs of
      		      []     -> []
      		      (y:ys) -> case n of 
      				  I# n# -> case n# of
      					     0 -> []
      					     _ -> drop (I# (n# -# 1#)) xs
      
      Notice that the recursive call has an explicit constructor as argument.
      Noticing this, we can make a specialised version of drop
      	
      	RULE: drop (I# n#) xs ==> drop' n# xs
      
      	drop' n# xs = let n = I# n# in ...orig RHS...
      
      Now the simplifier will apply the specialisation in the rhs of drop', giving
      
      	drop' n# xs = case xs of
      		      []     -> []
      		      (y:ys) -> case n# of
      				  0 -> []
      				  _ -> drop (n# -# 1#) xs
      
      Much better!  
      
      We'd also like to catch cases where a parameter is carried along unchanged,
      but evaluated each time round the loop:
      
      	f i n = if i>0 || i>n then i else f (i*2) n
      
      Here f isn't strict in n, but we'd like to avoid evaluating it each iteration.
      In Core, by the time we've w/wd (f is strict in i) we get
      
      	f i# n = case i# ># 0 of
      		   False -> I# i#
      		   True  -> case n of n' { I# n# ->
      			    case i# ># n# of
      				False -> I# i#
      				True  -> f (i# *# 2#) n'
      
      At the call to f, we see that the argument, n is know to be (I# n#),
      and n is evaluated elsewhere in the body of f, so we can play the same
      trick as above.  However we don't want to do that if the boxed version
      of n is needed (else we'd avoid the eval but pay more for re-boxing n).
      So in this case we want that the *only* uses of n are in case statements.
      
      
      So we look for
      
      * A self-recursive function.  Ignore mutual recursion for now, 
        because it's less common, and the code is simpler for self-recursion.
      
      * EITHER
      
         a) At a recursive call, one or more parameters is an explicit 
            constructor application
      	AND
            That same parameter is scrutinised by a case somewhere in 
            the RHS of the function
      
        OR
      
          b) At a recursive call, one or more parameters has an unfolding
             that is an explicit constructor application
      	AND
            That same parameter is scrutinised by a case somewhere in 
            the RHS of the function
      	AND
            Those are the only uses of the parameter
      12e6a9a5
  38. 27 Feb, 2001 1 commit