1. 25 Jan, 2006 1 commit
    • simonpj@microsoft.com's avatar
      Simon's big boxy-type commit · ac10f840
      simonpj@microsoft.com authored
      This very large commit adds impredicativity to GHC, plus
      numerous other small things.
        
      *** WARNING: I have compiled all the libraries, and
      ***	     a stage-2 compiler, and everything seems
      ***	     fine.  But don't grab this patch if you 
      ***	     can't tolerate a hiccup if something is
      ***	     broken.
        
      The big picture is this:
      
      a) GHC handles impredicative polymorphism, as described in the
         "Boxy types: type inference for higher-rank types and
         impredicativity" paper
      
      b) GHC handles GADTs in the new simplified (and very sligtly less
         epxrssive) way described in the
         "Simple unification-based type inference for GADTs" paper
      
        
      But there are lots of smaller changes, and since it was pre-Darcs
      they are not individually recorded.
        
      Some things to watch out for:
        
      c)   The story on lexically-scoped type variables has changed, as per
           my email.  I append the story below for completeness, but I 
           am still not happy with it, and it may change again.  In particular,
           the new story does not allow a pattern-bound scoped type variable
           to be wobbly, so (\(x::[a]) -> ...) is usually rejected.  This is
           more restrictive than before, and we might loosen up again.
        
      d)   A consequence of adding impredicativity is that GHC is a bit less
           gung ho about converting automatically between
        	(ty1 -> forall a. ty2)    and    (forall a. ty1 -> ty2)
           In particular, you may need to eta-expand some functions to make
           typechecking work again.
         
           Furthermore, functions are now invariant in their argument types,
           rather than being contravariant.  Again, the main consequence is
           that you may occasionally need to eta-expand function arguments when
           using higher-rank polymorphism.
        
      
      Please test, and let me know of any hiccups
      
      
      Scoped type variables in GHC
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      	January 2006
      
      0) Terminology.
         
         A *pattern binding* is of the form
      	pat = rhs
      
         A *function binding* is of the form
      	f pat1 .. patn = rhs
      
         A binding of the formm
      	var = rhs
         is treated as a (degenerate) *function binding*.
      
      
         A *declaration type signature* is a separate type signature for a
         let-bound or where-bound variable:
      	f :: Int -> Int
      
         A *pattern type signature* is a signature in a pattern: 
      	\(x::a) -> x
      	f (x::a) = x
      
         A *result type signature* is a signature on the result of a
         function definition:
      	f :: forall a. [a] -> a
      	head (x:xs) :: a = x
      
         The form
      	x :: a = rhs
         is treated as a (degnerate) function binding with a result
         type signature, not as a pattern binding.
      
      1) The main invariants:
      
           A) A lexically-scoped type variable always names a (rigid)
       	type variable (not an arbitrary type).  THIS IS A CHANGE.
              Previously, a scoped type variable named an arbitrary *type*.
      
           B) A type signature always describes a rigid type (since
      	its free (scoped) type variables name rigid type variables).
      	This is also a change, a consequence of (A).
      
           C) Distinct lexically-scoped type variables name distinct
      	rigid type variables.  This choice is open; 
      
      2) Scoping
      
      2(a) If a declaration type signature has an explicit forall, those type
         variables are brought into scope in the right hand side of the 
         corresponding binding (plus, for function bindings, the patterns on
         the LHS).  
      	f :: forall a. a -> [a]
      	f (x::a) = [x :: a, x]
         Both occurences of 'a' in the second line are bound by 
         the 'forall a' in the first line
      
         A declaration type signature *without* an explicit top-level forall
         is implicitly quantified over all the type variables that are
         mentioned in the type but not already in scope.  GHC's current
         rule is that this implicit quantification does *not* bring into scope
         any new scoped type variables.
      	f :: a -> a
      	f x = ...('a' is not in scope here)...
         This gives compatibility with Haskell 98
      
      2(b) A pattern type signature implicitly brings into scope any type
         variables mentioned in the type that are not already into scope.
         These are called *pattern-bound type variables*.
      	g :: a -> a -> [a]
      	g (x::a) (y::a) = [y :: a, x]
         The pattern type signature (x::a) brings 'a' into scope.
         The 'a' in the pattern (y::a) is bound, as is the occurrence on 
         the RHS.  
      
         A pattern type siganture is the only way you can bring existentials 
         into scope.
      	data T where
      	  MkT :: forall a. a -> (a->Int) -> T
      
      	f x = case x of
      		MkT (x::a) f -> f (x::a)
      
      2a) QUESTION
      	class C a where
      	  op :: forall b. b->a->a
      
      	instance C (T p q) where
      	  op = <rhs>
          Clearly p,q are in scope in <rhs>, but is 'b'?  Not at the moment.
          Nor can you add a type signature for op in the instance decl.
          You'd have to say this:
      	instance C (T p q) where
      	  op = let op' :: forall b. ...
      	           op' = <rhs>
      	       in op'
      
      3) A pattern-bound type variable is allowed only if the pattern's
         expected type is rigid.  Otherwise we don't know exactly *which*
         skolem the scoped type variable should be bound to, and that means
         we can't do GADT refinement.  This is invariant (A), and it is a 
         big change from the current situation.
      
      	f (x::a) = x	-- NO; pattern type is wobbly
      	
      	g1 :: b -> b
      	g1 (x::b) = x	-- YES, because the pattern type is rigid
      
      	g2 :: b -> b
      	g2 (x::c) = x	-- YES, same reason
      
      	h :: forall b. b -> b
      	h (x::b) = x	-- YES, but the inner b is bound
      
      	k :: forall b. b -> b
      	k (x::c) = x	-- NO, it can't be both b and c
      
      3a) You cannot give different names for the same type variable in the same scope
          (Invariant (C)):
      
      	f1 :: p -> p -> p		-- NO; because 'a' and 'b' would be
      	f1 (x::a) (y::b) = (x::a)	--     bound to the same type variable
      
      	f2 :: p -> p -> p		-- OK; 'a' is bound to the type variable
      	f2 (x::a) (y::a) = (x::a)	--     over which f2 is quantified
      					-- NB: 'p' is not lexically scoped
      
      	f3 :: forall p. p -> p -> p	-- NO: 'p' is now scoped, and is bound to
      	f3 (x::a) (y::a) = (x::a)	--     to the same type varialble as 'a'
      
      	f4 :: forall p. p -> p -> p	-- OK: 'p' is now scoped, and its occurences
      	f4 (x::p) (y::p) = (x::p)	--     in the patterns are bound by the forall
      
      
      3b) You can give a different name to the same type variable in different
          disjoint scopes, just as you can (if you want) give diferent names to 
          the same value parameter
      
      	g :: a -> Bool -> Maybe a
      	g (x::p) True  = Just x  :: Maybe p
      	g (y::q) False = Nothing :: Maybe q
      
      3c) Scoped type variables respect alpha renaming. For example, 
          function f2 from (3a) above could also be written:
      	f2' :: p -> p -> p
      	f2' (x::b) (y::b) = x::b
         where the scoped type variable is called 'b' instead of 'a'.
      
      
      4) Result type signatures obey the same rules as pattern types signatures.
         In particular, they can bind a type variable only if the result type is rigid
      
      	f x :: a = x	-- NO
      
      	g :: b -> b
      	g x :: b = x	-- YES; binds b in rhs
      
      5) A *pattern type signature* in a *pattern binding* cannot bind a 
         scoped type variable
      
      	(x::a, y) = ...		-- Legal only if 'a' is already in scope
      
         Reason: in type checking, the "expected type" of the LHS pattern is
         always wobbly, so we can't bind a rigid type variable.  (The exception
         would be for an existential type variable, but existentials are not
         allowed in pattern bindings either.)
       
         Even this is illegal
      	f :: forall a. a -> a
      	f x = let ((y::b)::a, z) = ... 
      	      in 
         Here it looks as if 'b' might get a rigid binding; but you can't bind
         it to the same skolem as a.
      
      6) Explicitly-forall'd type variables in the *declaration type signature(s)*
         for a *pattern binding* do not scope AT ALL.
      
      	x :: forall a. a->a	  -- NO; the forall a does 
      	Just (x::a->a) = Just id  --     not scope at all
      
      	y :: forall a. a->a
      	Just y = Just (id :: a->a)  -- NO; same reason
      
         THIS IS A CHANGE, but one I bet that very few people will notice.
         Here's why:
      
      	strange :: forall b. (b->b,b->b)
      	strange = (id,id)
      
      	x1 :: forall a. a->a
      	y1 :: forall b. b->b
      	(x1,y1) = strange
      
          This is legal Haskell 98 (modulo the forall). If both 'a' and 'b'
          both scoped over the RHS, they'd get unified and so cannot stand
          for distinct type variables. One could *imagine* allowing this:
         
      	x2 :: forall a. a->a
      	y2 :: forall a. a->a
      	(x2,y2) = strange
      
          using the very same type variable 'a' in both signatures, so that
          a single 'a' scopes over the RHS.  That seems defensible, but odd,
          because though there are two type signatures, they introduce just
          *one* scoped type variable, a.
      
      7) Possible extension.  We might consider allowing
      	\(x :: [ _ ]) -> <expr>
          where "_" is a wild card, to mean "x has type list of something", without
          naming the something.
      ac10f840
  2. 11 Jan, 2006 1 commit
  3. 06 Jan, 2006 1 commit
    • simonmar's avatar
      [project @ 2006-01-06 16:30:17 by simonmar] · 9d7da331
      simonmar authored
      Add support for UTF-8 source files
      
      GHC finally has support for full Unicode in source files.  Source
      files are now assumed to be UTF-8 encoded, and the full range of
      Unicode characters can be used, with classifications recognised using
      the implementation from Data.Char.  This incedentally means that only
      the stage2 compiler will recognise Unicode in source files, because I
      was too lazy to port the unicode classifier code into libcompat.
      
      Additionally, the following synonyms for keywords are now recognised:
      
        forall symbol 	(U+2200)	forall
        right arrow   	(U+2192)	->
        left arrow   		(U+2190)	<-
        horizontal ellipsis 	(U+22EF)	..
      
      there are probably more things we could add here.
      
      This will break some source files if Latin-1 characters are being used.
      In most cases this should result in a UTF-8 decoding error.  Later on
      if we want to support more encodings (perhaps with a pragma to specify
      the encoding), I plan to do it by recoding into UTF-8 before parsing.
      
      Internally, there were some pretty big changes:
      
        - FastStrings are now stored in UTF-8
      
        - Z-encoding has been moved right to the back end.  Previously we
          used to Z-encode every identifier on the way in for simplicity,
          and only decode when we needed to show something to the user.
          Instead, we now keep every string in its UTF-8 encoding, and
          Z-encode right before printing it out.  To avoid Z-encoding the
          same string multiple times, the Z-encoding is cached inside the
          FastString the first time it is requested.
      
          This speeds up the compiler - I've measured some definite
          improvement in parsing at least, and I expect compilations overall
          to be faster too.  It also cleans up a lot of cruft from the
          OccName interface.  Z-encoding is nicely hidden inside the
          Outputable instance for Names & OccNames now.
      
        - StringBuffers are UTF-8 too, and are now represented as
          ForeignPtrs.
      
        - I've put together some test cases, not by any means exhaustive,
          but there are some interesting UTF-8 decoding error cases that
          aren't obvious.  Also, take a look at unicode001.hs for a demo.
      9d7da331
  4. 04 Apr, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-04-04 11:55:11 by simonpj] · d551dbfe
      simonpj authored
      This commit combines three overlapping things:
      
      1.  Make rebindable syntax work for do-notation. The idea
          here is that, in particular, (>>=) can have a type that
          has class constraints on its argument types, e.g.
             (>>=) :: (Foo m, Baz a) => m a -> (a -> m b) -> m b
          The consequence is that a BindStmt and ExprStmt must have
          individual evidence attached -- previously it was one
          batch of evidence for the entire Do
          
          Sadly, we can't do this for MDo, because we use bind at
          a polymorphic type (to tie the knot), so we still use one
          blob of evidence (now in the HsStmtContext) for MDo.
          
          For arrow syntax, the evidence is in the HsCmd.
          
          For list comprehensions, it's all built-in anyway.
          
          So the evidence on a BindStmt is only used for ordinary
          do-notation.
      
      2.  Tidy up HsSyn.  In particular:
      
      	- Eliminate a few "Out" forms, which we can manage
      	without (e.g. 
      
      	- It ought to be the case that the type checker only
      	decorates the syntax tree, but doesn't change one
      	construct into another.  That wasn't true for NPat,
      	LitPat, NPlusKPat, so I've fixed that.
      
      	- Eliminate ResultStmts from Stmt.  They always had
      	to be the last Stmt, which led to awkward pattern
      	matching in some places; and the benefits didn't seem
      	to outweigh the costs.  Now each construct that uses
      	[Stmt] has a result expression too (e.g. GRHS).
      
      
      3.  Make 'deriving( Ix )' generate a binding for unsafeIndex,
          rather than for index.  This is loads more efficient.
      
          (This item only affects TcGenDeriv, but some of point (2)
          also affects TcGenDeriv, so it has to be in one commit.)
      d551dbfe
  5. 31 Mar, 2005 1 commit
    • simonmar's avatar
      [project @ 2005-03-31 10:16:33 by simonmar] · 853e20a3
      simonmar authored
      Tweaks to get the GHC sources through Haddock.  Doesn't quite work
      yet, because Haddock complains about the recursive modules.  Haddock
      needs to understand SOURCE imports (it can probably just ignore them
      as a first attempt).
      853e20a3
  6. 01 Mar, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-03-01 05:49:43 by simonpj] · 6d36af4a
      simonpj authored
      Make desugaring of pattern-matching much more civilised.
      
      Before this change we wrapped new bindings around the
      right hand side; but that meant they ended up wrapped
      in reverse order.  Now we accumulate the bindings
      separately, in the eqn_wrap field of an EqnInfo.
      
      This cures a desugaring bug encountered by Akos Korosmezey
      immortalised as ds055
      6d36af4a
  7. 27 Jan, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-01-27 10:44:00 by simonpj] · 508a505e
      simonpj authored
      --------------------------------------------
                Replace hi-boot files with hs-boot files
        	--------------------------------------------
      
      This major commit completely re-organises the way that recursive modules
      are dealt with.
      
        * It should have NO EFFECT if you do not use recursive modules
      
        * It is a BREAKING CHANGE if you do
      
      ====== Warning: .hi-file format has changed, so if you are
      ======		updating into an existing HEAD build, you'll
      ======		need to make clean and re-make
      
      
      The details:  [documentation still to be done]
      
      * Recursive loops are now broken with Foo.hs-boot (or Foo.lhs-boot),
        not Foo.hi-boot
      
      * An hs-boot files is a proper source file.  It is compiled just like
        a regular Haskell source file:
      	ghc Foo.hs		generates Foo.hi, Foo.o
      	ghc Foo.hs-boot		generates Foo.hi-boot, Foo.o-boot
      
      * hs-boot files are precisely a subset of Haskell. In particular:
      	- they have the same import, export, and scoping rules
      	- errors (such as kind errors) in hs-boot files are checked
        You do *not* need to mention the "original" name of something in
        an hs-boot file, any more than you do in any other Haskell module.
      
      * The Foo.hi-boot file generated by compiling Foo.hs-boot is a machine-
        generated interface file, in precisely the same format as Foo.hi
      
      * When compiling Foo.hs, its exports are checked for compatibility with
        Foo.hi-boot (previously generated by compiling Foo.hs-boot)
      
      * The dependency analyser (ghc -M) knows about Foo.hs-boot files, and
        generates appropriate dependencies.  For regular source files it
        generates
      	Foo.o : Foo.hs
      	Foo.o : Baz.hi		-- Foo.hs imports Baz
      	Foo.o : Bog.hi-boot	-- Foo.hs source-imports Bog
      
        For a hs-boot file it generates similar dependencies
      	Bog.o-boot : Bog.hs-boot
      	Bog.o-boot : Nib.hi	-- Bog.hs-boto imports Nib
      
      * ghc -M is also enhanced to use the compilation manager dependency
        chasing, so that
      	ghc -M Main
        will usually do the job.  No need to enumerate all the source files.
      
      * The -c flag is no longer a "compiler mode". It simply means "omit the
        link step", and synonymous with -no-link.
      508a505e
  8. 22 Dec, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-12-22 12:06:13 by simonpj] · d7c402a3
      simonpj authored
      ----------------------------------------
           New Core invariant: keep case alternatives in sorted order
      	----------------------------------------
      
      We now keep the alternatives of a Case in the Core language in sorted
      order.  Sorted, that is,
      	by constructor tag	for DataAlt
      	by literal		for LitAlt
      
      The main reason is that it makes matching and equality testing more robust.
      But in fact some lines of code vanished from SimplUtils.mkAlts.
      
      
      WARNING: no change to interface file formats, but you'll need to recompile
      your libraries so that they generate interface files that respect the
      invariant.
      d7c402a3
  9. 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
  10. 06 Apr, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-04-06 09:29:49 by simonpj] · 3f885dcb
      simonpj authored
      The "rebindable-syntax" stuff wasn't dealing with the new location
      information correctly.  This commit fixes the problem, and thereby
      makes mdofail004 work right.  Maybe others too.
      3f885dcb
  11. 10 Dec, 2003 1 commit
    • simonmar's avatar
      [project @ 2003-12-10 14:15:16 by simonmar] · 55042138
      simonmar authored
      Add accurate source location annotations to HsSyn
      -------------------------------------------------
      
      Every syntactic entity in HsSyn is now annotated with a SrcSpan, which
      details the exact beginning and end points of that entity in the
      original source file.  All honest compilers should do this, and it was
      about time GHC did the right thing.
      
      The most obvious benefit is that we now have much more accurate error
      messages; when running GHC inside emacs for example, the cursor will
      jump to the exact location of an error, not just a line somewhere
      nearby.  We haven't put a huge amount of effort into making sure all
      the error messages are accurate yet, so there could be some tweaking
      still needed, although the majority of messages I've seen have been
      spot-on.
      
      Error messages now contain a column number in addition to the line
      number, eg.
      
         read001.hs:25:10: Variable not in scope: `+#'
      
      To get the full text span info, use the new option -ferror-spans.  eg.
      
         read001.hs:25:10-11: Variable not in scope: `+#'
      
      I'm not sure whether we should do this by default.  Emacs won't
      understand the new error format, for one thing.
      
      In a more elaborate editor setting (eg. Visual Studio), we can arrange
      to actually highlight the subexpression containing an error.  Eventually
      this information will be used so we can find elements in the abstract
      syntax corresponding to text locations, for performing high-level editor
      functions (eg. "tell me the type of this expression I just highlighted").
      
      Performance of the compiler doesn't seem to be adversely affected.
      Parsing is still quicker than in 6.0.1, for example.
      
      Implementation:
      
      This was an excrutiatingly painful change to make: both Simon P.J. and
      myself have been working on it for the last three weeks or so.  The
      basic changes are:
      
       - a new datatype SrcSpan, which represents a beginning and end position
         in a source file.
      
       - To reduce the pain as much as possible, we also defined:
      
            data Located e = L SrcSpan e
      
       - Every datatype in HsSyn has an equivalent Located version.  eg.
      
            type LHsExpr id = Located (HsExpr id)
      
         and pretty much everywhere we used to use HsExpr we now use
         LHsExpr.  Believe me, we thought about this long and hard, and
         all the other options were worse :-)
      
      
      Additional changes/cleanups we made at the same time:
      
        - The abstract syntax for bindings is now less arcane.  MonoBinds
          and HsBinds with their built-in list constructors have gone away,
          replaced by HsBindGroup and HsBind (see HsSyn/HsBinds.lhs).
      
        - The various HsSyn type synonyms have now gone away (eg. RdrNameHsExpr,
          RenamedHsExpr, and TypecheckedHsExpr are now HsExpr RdrName,
          HsExpr Name, and HsExpr Id respectively).
      
        - Utilities over HsSyn are now collected in a new module HsUtils.
          More stuff still needs to be moved in here.
      
        - MachChar now has a real Char instead of an Int.  All GHC versions that
          can compile GHC now support 32-bit Chars, so this was a simplification.
      55042138
  12. 17 Nov, 2003 1 commit
  13. 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
  14. 15 Jul, 2003 1 commit
  15. 24 Jun, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-06-24 07:58:18 by simonpj] · 16e4ce4c
      simonpj authored
      ----------------------------------------------
      	Add support for Ross Paterson's arrow notation
      	----------------------------------------------
      
      Ross Paterson's ICFP'01 paper described syntax to support John Hughes's
      "arrows", rather as do-notation supports monads.  Except that do-notation is
      relatively modest -- you can write monads by hand without much trouble --
      whereas arrow-notation is more-or-less essential for writing arrow programs.
      It desugars to a massive pile of tuple construction and selection!
      
      For some time, Ross has had a pre-processor for arrow notation, but the
      resulting type error messages (reported in terms of the desugared code)
      are impenetrable.  This commit integrates the syntax into GHC.  The
      type error messages almost certainly still require tuning, but they should
      be better than with the pre-processor.
      
      Main syntactic changes (enabled with -farrows)
      
         exp ::= ... | proc pat -> cmd
      
         cmd ::= exp1 -<  exp2   |  exp1 >-  exp2
      	|  exp1 -<< exp2   |  exp1 >>- exp2
      	| \ pat1 .. patn -> cmd
      	| let decls in cmd
      	| if exp then cmd1 else cmd2
      	| do { cstmt1 .. cstmtn ; cmd }
      	| (| exp |) cmd1 .. cmdn
      	| cmd1 qop cmd2
      	| case exp of { calts }
      
         cstmt :: = let decls
      	 |   pat <- cmd
      	 |   rec { cstmt1 .. cstmtn }
      	 |   cmd
      
      New keywords and symbols:
      	proc rec
      	-<   >-   -<<   >>-
      	(|  |)
      
      The do-notation in cmds was not described in Ross's ICFP'01 paper; instead
      it's in his chapter in The Fun of Programming (Plagrave 2003).
      
      The four arrow-tail forms (-<) etc cover
        (a) which order the pices come in (-<  vs  >-), and
        (b) whether the locally bound variables can be used in the
      		arrow part (-<  vs  -<<) .
      In previous presentations, the higher-order-ness (b) was inferred,
      but it makes a big difference to the typing required so it seems more
      consistent to be explicit.
      
      The 'rec' form is also available in do-notation:
        * you can use 'rec' in an ordinary do, with the obvious meaning
        * using 'mdo' just says "infer the minimal recs"
      
      
      Still to do
      ~~~~~~~~~~~
      Top priority is the user manual.
      
      The implementation still lacks an implementation of
      the case form of cmd.
      
      
      Implementation notes
      ~~~~~~~~~~~~~~~~~~~~
      Cmds are parsed, and indeed renamed, as expressions.  The type checker
      distinguishes the two.
      16e4ce4c
  16. 03 Jun, 2003 1 commit
  17. 02 Jun, 2003 3 commits
    • simonpj's avatar
      [project @ 2003-06-02 16:10:19 by simonpj] · 6d7921bb
      simonpj authored
      Wibbles to tuples
      6d7921bb
    • simonpj's avatar
      [project @ 2003-06-02 14:26:54 by simonpj] · eda83294
      simonpj authored
      Wibbles to nested tuples
      eda83294
    • simonpj's avatar
      [project @ 2003-06-02 13:28:08 by simonpj] · 663a01b2
      simonpj authored
      -------------------------------------
            Fix the big-tuple-from-desugaring problem
      	-------------------------------------
      
      The desugarer generates a tuple from
      	- mutually recursive bindings
      	- pattern bindings
      
      If either bind a lot of variables, GHC can generate a big
      tuple that isn't in the library, with subsequent disaster.
      
      This commit fixes the problem, by using nested tuples.  It
      does *not* fix the problem with big tuples written by the
      user. And there's still a potential desugarer problem with
      parallel list comprehensions that bind a lot of variables
      (and parallel array comprehensions) -- but I expect they are
      much much rarer.
      
      The fix isn't fully tested yet -- I'll try to do that today.
      663a01b2
  18. 07 Nov, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-11-07 11:42:48 by simonpj] · 06fa575f
      simonpj authored
      ------------------
      	Fix an obscure bug in implicit parameters,
      	interacting with lazy pattern matching
      		------------------
      
      		MERGE TO STABLE BRANCH
      
      The problem was this:
      
        data UniqueSupply = US Integer
      
        newUnique :: (?uniqueSupply :: UniqueSupply) => Integer
        newUnique = r
                  where US r = ?uniqueSupply
      
      The lazy pattern match in the where clause killed GHC 5.04 because the
      SourceType {?uniqueSupply::UniqueSupply} of the RHS of the 'where' didn't
      look like a UniqueSupply.
      
      The fix is simple: in DsUtils.mkSelectorBinds, use the pattern, not
      the rhs, to get the type reqd.  More efficient too.
      
      Test is typecheck/should_compile/tc164.hs
      06fa575f
  19. 30 Oct, 2002 1 commit
  20. 09 Oct, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-10-09 15:03:48 by simonpj] · 8c1b6bd7
      simonpj authored
      -----------------------------------
      	Lots more Template Haskell stuff
      	-----------------------------------
      
      At last!  Top-level declaration splices work!
      Syntax is
      
      	$(f x)
      
      not "splice (f x)" as in the paper.
      
      Lots jiggling around, particularly with the top-level plumbining.
      Note the new data type HsDecls.HsGroup.
      8c1b6bd7
  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. 29 Apr, 2002 1 commit
    • simonmar's avatar
      [project @ 2002-04-29 14:03:38 by simonmar] · b085ee40
      simonmar authored
      FastString cleanup, stage 1.
      
      The FastString type is no longer a mixture of hashed strings and
      literal strings, it contains hashed strings only with O(1) comparison
      (except for UnicodeStr, but that will also go away in due course).  To
      create a literal instance of FastString, use FSLIT("..").
      
      By far the most common use of the old literal version of FastString
      was in the pattern
      
      	  ptext SLIT("...")
      
      this combination still works, although it doesn't go via FastString
      any more.  The next stage will be to remove the need to use this
      special combination at all, using a RULE.
      
      To convert a FastString into an SDoc, now use 'ftext' instead of
      'ptext'.
      
      I've also removed all the FAST_STRING related macros from HsVersions.h
      except for SLIT and FSLIT, just use the relevant functions from
      FastString instead.
      b085ee40
  23. 11 Apr, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-04-11 12:03:29 by simonpj] · a7b95beb
      simonpj authored
      -------------------
      	Mainly derived Read
      	-------------------
      
      This commit is a tangle of several things that somehow got wound up
      together, I'm afraid.
      
      
      The main course
      ~~~~~~~~~~~~~~~
      Replace the derived-Read machinery with Koen's cunning new parser
      combinator library.   The result should be
      	* much smaller code sizes from derived Read
      	* faster execution of derived Read
      
      WARNING: I have not thoroughly tested this stuff; I'd be glad if you did!
      	 All the hard work is done, but there may be a few nits.
      
      The Read class gets two new methods, not exposed
      in the H98 inteface of course:
        class Read a where
          readsPrec    :: Int -> ReadS a
          readList     :: ReadS [a]
          readPrec     :: ReadPrec a		-- NEW
          readListPrec :: ReadPrec [a]	-- NEW
      
      There are the following new libraries:
      
        Text.ParserCombinators.ReadP		Koens combinator parser
        Text.ParserCombinators.ReadPrec	Ditto, but with precedences
      
        Text.Read.Lex				An emasculated lexical analyser
      					that provides the functionality
      					of H98 'lex'
      
      TcGenDeriv is changed to generate code that uses the new libraries.
      The built-in instances of Read (List, Maybe, tuples, etc) use the new
      libraries.
      
      
      Other stuff
      ~~~~~~~~~~~
      1. Some fixes the the plumbing of external-core generation. Sigbjorn
      did most of the work earlier, but this commit completes the renaming and
      typechecking plumbing.
      
      2. Runtime error-generation functions, such as GHC.Err.recSelErr,
      GHC.Err.recUpdErr, etc, now take an Addr#, pointing to a UTF8-encoded
      C string, instead of a Haskell string.  This makes the *calls* to these
      functions easier to generate, and smaller too, which is a good thing.
      
      In particular, it means that MkId.mkRecordSelectorId doesn't need to
      be passed "unpackCStringId", which was GRUESOME; and that in turn means
      that tcTypeAndClassDecls doesn't need to be passed unf_env, which is
      a very worthwhile cleanup.   Win/win situation.
      
      3.  GHC now faithfully translates do-notation using ">>" for statements
      with no binding, just as the report says.  While I was there I tidied
      up HsDo to take a list of Ids instead of 3 (but now 4) separate Ids.
      Saves a bit of code here and there.  Also introduced Inst.newMethodFromName
      to package a common idiom.
      a7b95beb
  24. 05 Apr, 2002 1 commit
  25. 01 Apr, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-04-01 08:23:30 by simonpj] · 9003a18c
      simonpj authored
      ------------------------------------
      	Change the treatment of the stupid
      	   context on data constructors
      	-----------------------------------
      
      Data types can have a context:
      
      	data (Eq a, Ord b) => T a b = T1 a b | T2 a
      
      and that makes the constructors have a context too
      (notice that T2's context is "thinned"):
      
      	T1 :: (Eq a, Ord b) => a -> b -> T a b
      	T2 :: (Eq a) => a -> T a b
      
      Furthermore, this context pops up when pattern matching
      (though GHC hasn't implemented this, but it is in H98, and
      I've fixed GHC so that it now does):
      
      	f (T2 x) = x
      gets inferred type
      	f :: Eq a => T a b -> a
      
      I say the context is "stupid" because the dictionaries passed
      are immediately discarded -- they do nothing and have no benefit.
      It's a flaw in the language.
      
      Up to now I have put this stupid context into the type of
      the "wrapper" constructors functions, T1 and T2, but that turned
      out to be jolly inconvenient for generics, and record update, and
      other functions that build values of type T (because they don't
      have suitable dictionaries available).
      
      So now I've taken the stupid context out.  I simply deal with
      it separately in the type checker on occurrences of a constructor,
      either in an expression or in a pattern.
      
      To this end
      
      * Lots of changes in DataCon, MkId
      
      * New function Inst.tcInstDataCon to instantiate a data constructor
      
      
      
      I also took the opportunity to
      
      * Rename
      	dataConId --> dataConWorkId
        for consistency.
      
      * Tidied up MkId.rebuildConArgs quite a bit, and renamed it
      	mkReboxingAlt
      
      * Add function DataCon.dataConExistentialTyVars, with the obvious meaning
      9003a18c
  26. 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
  27. 26 Nov, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-11-26 09:20:25 by simonpj] · 5e3f005d
      simonpj authored
      ----------------------
      	Implement Rank-N types
      	----------------------
      
      This commit implements the full glory of Rank-N types, using
      the Odersky/Laufer approach described in their paper
      	"Putting type annotations to work"
      
      In fact, I've had to adapt their approach to deal with the
      full glory of Haskell (including pattern matching, and the
      scoped-type-variable extension).  However, the result is:
      
      * There is no restriction to rank-2 types.  You can nest forall's
        as deep as you like in a type.  For example, you can write a type
        like
      	p :: ((forall a. Eq a => a->a) -> Int) -> Int
        This is a rank-3 type, illegal in GHC 5.02
      
      * When matching types, GHC uses the cunning Odersky/Laufer coercion
        rules.  For example, suppose we have
      	q :: (forall c. Ord c => c->c) -> Int
        Then, is this well typed?
      	x :: Int
      	x = p q
        Yes, it is, but GHC has to generate the right coercion.  Here's
        what it looks like with all the big lambdas and dictionaries put in:
      
      	x = p (\ f :: (forall a. Eq a => a->a) ->
      		 q (/\c \d::Ord c -> f c (eqFromOrd d)))
      
        where eqFromOrd selects the Eq superclass dictionary from the Ord
        dicationary:		eqFromOrd :: Ord a -> Eq a
      
      
      * You can use polymorphic types in pattern type signatures.  For
        example:
      
      	f (g :: forall a. a->a) = (g 'c', g True)
      
        (Previously, pattern type signatures had to be monotypes.)
      
      * The basic rule for using rank-N types is that you must specify
        a type signature for every binder that you want to have a type
        scheme (as opposed to a plain monotype) as its type.
      
        However, you don't need to give the type signature on the
        binder (as I did above in the defn for f).  You can give it
        in a separate type signature, thus:
      
      	f :: (forall a. a->a) -> (Char,Bool)
      	f g = (g 'c', g True)
      
        GHC will push the external type signature inwards, and use
        that information to decorate the binders as it comes across them.
        I don't have a *precise* specification of this process, but I
        think it is obvious enough in practice.
      
      * In a type synonym you can use rank-N types too.  For example,
        you can write
      
      	type IdFun = forall a. a->a
      
      	f :: IdFun -> (Char,Bool)
      	f g = (g 'c', g True)
      
        As always, type synonyms must always occur saturated; GHC
        expands them before it does anything else.  (Still, GHC goes
        to some trouble to keep them unexpanded in error message.)
      
      
      The main plan is as before.  The main typechecker for expressions,
      tcExpr, takes an "expected type" as its argument.  This greatly
      improves error messages.  The new feature is that when this
      "expected type" (going down) meets an "actual type" (coming up)
      we use the new subsumption function
      	TcUnify.tcSub
      which checks that the actual type can be coerced into the
      expected type (and produces a coercion function to demonstrate).
      
      The main new chunk of code is TcUnify.tcSub.  The unifier itself
      is unchanged, but it has moved from TcMType into TcUnify.  Also
      checkSigTyVars has moved from TcMonoType into TcUnify.
      Result: the new module, TcUnify, contains all stuff relevant
      to subsumption and unification.
      
      Unfortunately, there is now an inevitable loop between TcUnify
      and TcSimplify, but that's just too bad (a simple TcUnify.hi-boot
      file).
      
      
      All of this doesn't come entirely for free.  Here's the typechecker
      line count (INCLUDING comments)
      	Before	16,551
      	After	17,116
      5e3f005d
  28. 25 Oct, 2001 1 commit
    • sof's avatar
      [project @ 2001-10-25 02:13:10 by sof] · 9e933350
      sof authored
      - Pet peeve removal / code tidyup, replaced various sub-optimal
        uses of 'length' with something a bit better, i.e., replaced
        the following patterns
      
         *  length as `cmpOp` length bs
         *  length as `cmpOp` val   -- incl. uses where val == 1 and val == 0
         *  {take,drop,splitAt} (length as) bs
         *  length [ () | pat <- as ]
      
        with uses of misc Util functions.
      
        I'd be surprised if there's a noticeable reduction in running
        times as a result of these changes, but every little bit helps.
      
        [ The changes have been tested wrt testsuite/ - I'm seeing a couple
          of unexpected breakages coming from CorePrep, but I'm currently
          assuming that these are due to other recent changes. ]
      
      - compMan/CompManager.lhs: restored 4.08 compilability + some code
        cleanup.
      
      None of these changes are HEADworthy.
      9e933350
  29. 12 Jul, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-07-12 16:21:22 by simonpj] · ab46fd8e
      simonpj authored
      --------------------------------------------
      	Fix another bug in the squash-newtypes story.
      	--------------------------------------------
      
      [This one was spotted by Marcin, and is now enshrined in test tc130.]
      
      The desugarer straddles the boundary between the type checker and
      Core, so it sometimes needs to look through newtypes/implicit parameters
      and sometimes not.  This is really a bit painful, but I can't think of
      a better way to do it.
      
      The only simple way to fix things was to pass a bit more type
      information in the HsExpr type, from the type checker to the desugarer.
      That led to the non-local changes you can see.
      
      On the way I fixed one other thing.  In various HsSyn constructors
      there is a Type that is bogus (bottom) before the type checker, and
      filled in with a real type by the type checker.  In one place it was
      a (Maybe Type) which was Nothing before, and (Just ty) afterwards.
      I've defined a type synonym HsTypes.PostTcType for this, and a named
      bottom value HsTypes.placeHolderType to use when you want the bottom
      value.
      ab46fd8e
  30. 25 Jun, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-06-25 08:09:57 by simonpj] · d069cec2
      simonpj authored
      ----------------
      	Squash newtypes
      	----------------
      
      This commit squashes newtypes and their coerces, from the typechecker
      onwards.  The original idea was that the coerces would not get in the
      way of optimising transformations, but despite much effort they continue
      to do so.   There's no very good reason to retain newtype information
      beyond the typechecker, so now we don't.
      
      Main points:
      
      * The post-typechecker suite of Type-manipulating functions is in
      types/Type.lhs, as before.   But now there's a new suite in types/TcType.lhs.
      The difference is that in the former, newtype are transparent, while in
      the latter they are opaque.  The typechecker should only import TcType,
      not Type.
      
      * The operations in TcType are all non-monadic, and most of them start with
      "tc" (e.g. tcSplitTyConApp).  All the monadic operations (used exclusively
      by the typechecker) are in a new module, typecheck/TcMType.lhs
      
      * I've grouped newtypes with predicate types, thus:
      	data Type = TyVarTy Tyvar | ....
      		  | SourceTy SourceType
      
      	data SourceType = NType TyCon [Type]
      			| ClassP Class [Type]
      			| IParam Type
      
      [SourceType was called PredType.]  This is a little wierd in some ways,
      because NTypes can't occur in qualified types.   However, the idea is that
      a SourceType is a type that is opaque to the type checker, but transparent
      to the rest of the compiler, and newtypes fit that as do implicit parameters
      and dictionaries.
      
      * Recursive newtypes still retain their coreces, exactly as before. If
      they were transparent we'd get a recursive type, and that would make
      various bits of the compiler diverge (e.g. things which do type comparison).
      
      * I've removed types/Unify.lhs (non-monadic type unifier and matcher),
      merging it into TcType.
      
      Ditto typecheck/TcUnify.lhs (monadic unifier), merging it into TcMType.
      d069cec2
  31. 18 May, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-05-18 08:46:18 by simonpj] · b4775e5e
      simonpj authored
      -----------------------------
      	Get unbox-strict-fields right
      	-----------------------------
      
      The problem was that when a library was compiled *without* -funbox-strict-fields,
      and the main program was compiled *with* that flag, we were wrongly treating
      the fields of imported data types as unboxed.
      
      To fix this I added an extra constructor to StrictnessMark to express whether
      the "!" annotation came from an interface file (don't fiddle) or a source
      file (decide whether to unbox).
      
      On the way I tided things up:
      
      * StrictnessMark moves to Demand.lhs, and doesn't have the extra DataCon
        fields that kept it in DataCon before.
      
      * HsDecls.BangType has one constructor, not three, with a StrictnessMark field.
      
      * DataCon keeps track of its strictness signature (dcRepStrictness), but not
        its "user strict marks" (which were never used)
      
      * All the functions, like getUniquesDs, that used to take an Int saying how
        many uniques to allocate, now return an infinite list. This saves arguments
        and hassle.  But it involved touching quite a few files.
      
      * rebuildConArgs takes a list of Uniques to use as its unique supply.  This
        means I could combine DsUtils.rebuildConArgs with MkId.rebuildConArgs
        (hooray; the main point of the previous change)
      
      
      I also tidied up one or two error messages
      b4775e5e
  32. 26 Feb, 2001 1 commit
    • simonmar's avatar
      [project @ 2001-02-26 15:06:57 by simonmar] · 1c62b517
      simonmar authored
      Implement do-style bindings on the GHCi command line.
      
      The syntax for a command-line is exactly that of a do statement, with
      the following meanings:
      
        - `pat <- expr'
          performs expr, and binds each of the variables in pat.
      
        - `let pat = expr; ...'
          binds each of the variables in pat, doesn't do any evaluation
      
        - `expr'
          behaves as `it <- expr' if expr is IO-typed, or `let it = expr'
          followed by `print it' otherwise.
      1c62b517
  33. 07 Nov, 2000 1 commit
  34. 18 Oct, 2000 1 commit
  35. 28 Sep, 2000 1 commit
    • simonpj's avatar
      [project @ 2000-09-28 13:04:14 by simonpj] · 861e836e
      simonpj authored
      ------------------------------------
      	   Mainly PredTypes (28 Sept 00)
      	------------------------------------
      
      Three things in this commit:
      
      	1.  Main thing: tidy up PredTypes
      	2.  Move all Keys into PrelNames
      	3.  Check for unboxed tuples in function args
      
      1. Tidy up PredTypes
      ~~~~~~~~~~~~~~~~~~~~
      The main thing in this commit is to modify the representation of Types
      so that they are a (much) better for the qualified-type world.  This
      should simplify Jeff's life as he proceeds with implicit parameters
      and functional dependencies.  In particular, PredType, introduced by
      Jeff, is now blessed and dignified with a place in TypeRep.lhs:
      
      	data PredType  = Class  Class [Type]
      		       | IParam Name  Type
      
      Consider these examples:
      	f :: (Eq a) => a -> Int
      	g :: (?x :: Int -> Int) => a -> Int
      	h :: (r\l) => {r} => {l::Int | r}
      
      Here the "Eq a" and "?x :: Int -> Int" and "r\l" are all called
      *predicates*, and are represented by a PredType.  (We don't support
      TREX records yet, but the setup is designed to expand to allow them.)
      
      In addition, Type gains an extra constructor:
      
      	data Type = .... | PredTy PredType
      
      so that PredType is injected directly into Type.  So the type
      	p => t
      is represented by
      	PredType p `FunTy` t
      
      I have deleted the hackish IPNote stuff; predicates are dealt with entirely
      through PredTys, not through NoteTy at all.
      
      
      2.  Move Keys into PrelNames
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      This is just a housekeeping operation. I've moved all the pre-assigned Uniques
      (aka Keys) from Unique.lhs into PrelNames.lhs.  I've also moved knowKeyRdrNames
      from PrelInfo down into PrelNames.  This localises in PrelNames lots of stuff
      about predefined names.  Previously one had to alter three files to add one,
      now only one.
      
      3.  Unboxed tuples
      ~~~~~~~~~~~~~~~~~~
      Add a static check for unboxed tuple arguments.  E.g.
      	data T = T (# Int, Int #)
      is illegal
      861e836e
  36. 22 Sep, 2000 1 commit
    • simonpj's avatar
      [project @ 2000-09-22 15:56:12 by simonpj] · 1bba522f
      simonpj authored
      --------------------------------------------------
      	Tidying up HsLit, and making it possible to define
      		your own numeric library
      
      		Simon PJ 22 Sept 00
      	--------------------------------------------------
      
      ** NOTE: I did these changes on the aeroplane.  They should compile,
      	 and the Prelude still compiles OK, but it's entirely 
      	 possible that I've broken something
      
      The original reason for this many-file but rather shallow
      commit is that it's impossible in Haskell to write your own
      numeric library.  Why?  Because when you say '1' you get 
      (Prelude.fromInteger 1), regardless of what you hide from the
      Prelude, or import from other libraries you have written.  So the
      idea is to extend the -fno-implicit-prelude flag so that 
      in addition to no importing the Prelude, you can rebind 
      	fromInteger	-- Applied to literal constants
      	fromRational	-- Ditto
      	negate		-- Invoked by the syntax (-x)
      	the (-) used when desugaring n+k patterns
      
      After toying with other designs, I eventually settled on a simple,
      crude one: rather than adding a new flag, I just extended the
      semantics of -fno-implicit-prelude so that uses of fromInteger,
      fromRational and negate are all bound to "whatever is in scope" 
      rather than "the fixed Prelude functions".  So if you say
      
      	{-# OPTIONS -fno-implicit-prelude #-}
      	module M where
       	import MyPrelude( fromInteger )
      
      	x = 3
      
      the literal 3 will use whatever (unqualified) "fromInteger" is in scope,
      in this case the one gotten from MyPrelude.
      
      
      On the way, though, I studied how HsLit worked, and did a substantial tidy
      up, deleting quite a lot of code along the way.  In particular.
      
      * HsBasic.lhs is renamed HsLit.lhs.  It defines the HsLit type.
      
      * There are now two HsLit types, both defined in HsLit.
      	HsLit for non-overloaded literals (like 'x')
      	HsOverLit for overloaded literals (like 1 and 2.3)
      
      * HsOverLit completely replaces Inst.OverloadedLit, which disappears.
        An HsExpr can now be an HsOverLit as well as an HsLit.
      
      * HsOverLit carries the Name of the fromInteger/fromRational operation,
        so that the renamer can help with looking up the unqualified name 
        when -fno-implicit-prelude is on.  Ditto the HsExpr for negation.
        It's all very tidy now.
      
      * RdrHsSyn contains the stuff that handles -fno-implicit-prelude
        (see esp RdrHsSyn.prelQual).  RdrHsSyn also contains all the "smart constructors"
        used by the parser when building HsSyn.  See for example RdrHsSyn.mkNegApp
        (previously the renamer (!) did the business of turning (- 3#) into -3#).
      
      * I tidied up the handling of "special ids" in the parser.  There's much
        less duplication now.
      
      * Move Sven's Horner stuff to the desugarer, where it belongs.  
        There's now a nice function DsUtils.mkIntegerLit which brings together
        related code from no fewer than three separate places into one single
        place.  Nice!
      
      * A nice tidy-up in MatchLit.partitionEqnsByLit became possible.
      
      * Desugaring of HsLits is now much tidier (DsExpr.dsLit)
      
      * Some stuff to do with RdrNames is moved from ParseUtil.lhs to RdrHsSyn.lhs,
        which is where it really belongs.
      
      * I also removed 
      	many unnecessary imports from modules 
      	quite a bit of dead code
        in divers places
      1bba522f
  37. 07 Sep, 2000 1 commit
    • simonpj's avatar
      [project @ 2000-09-07 09:10:07 by simonpj] · c1994342
      simonpj authored
      * Make the desugarer use string equality for string literal
        patterns longer than 1 character.  And put a specialised
        eqString into PrelBase, with a suitable specialisation rule.
        This makes a huge difference to the size of the code generated
        by deriving(Read) notably in Time.lhs
      c1994342
  38. 07 Aug, 2000 1 commit
    • qrczak's avatar
      [project @ 2000-08-07 23:37:19 by qrczak] · 4b172698
      qrczak authored
      Now Char, Char#, StgChar have 31 bits (physically 32).
      "foo"# is still an array of bytes.
      
      CharRep represents 32 bits (on a 64-bit arch too). There is also
      Int8Rep, used in those places where bytes were originally meant.
      readCharArray, indexCharOffAddr etc. still use bytes. Storable and
      {I,M}Array use wide Chars.
      
      In future perhaps all sized integers should be primitive types. Then
      some usages of indexing primops scattered through the code could
      be changed to then-available Int8 ones, and then Char variants of
      primops could be made wide (other usages that handle text should use
      conversion that will be provided later).
      
      I/O and _ccall_ arguments assume ISO-8859-1. UTF-8 is internally used
      for string literals (only).
      
      Z-encoding is ready for Unicode identifiers.
      
      Ranges of intlike and charlike closures are more easily configurable.
      
      I've probably broken nativeGen/MachCode.lhs:chrCode for Alpha but I
      don't know the Alpha assembler to fix it (what is zapnot?). Generally
      I'm not sure if I've done the NCG changes right.
      
      This commit breaks the binary compatibility (of course).
      
      TODO:
      * is* and to{Lower,Upper} in Char (in progress).
      * Libraries for text conversion (in design / experiments),
        to be plugged to I/O and a higher level foreign library.
      * PackedString.
      * StringBuffer and accepting source in encodings other than ISO-8859-1.
      4b172698