1. 17 Jun, 2002 1 commit
  2. 23 May, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-05-23 15:51:26 by simonpj] · 61193fe4
      simonpj authored
      Don't report ambiguity errors
      	if other type errors have happened
      This saves a gratuitous error cascade when the type checker
      recovers from one error by giving f type (forall a.a), and
      then find an ambiguity problem as a direct result.
  3. 10 Apr, 2002 1 commit
  4. 02 Apr, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-04-02 13:21:36 by simonpj] · 13878c13
      simonpj authored
      	Fix two nasty, subtle loops in context simplification
      The context simplifier in TcSimplify was building a recursive
      dictionary, which meant the program looped when run.  The reason
      was pretty devious; in fact there are two independent causes.
      Cause 1
       	class Eq b => Foo a b
      	instance Eq a => Foo [a] a
      If we are reducing
      	d:Foo [t] t
      we'll first deduce that it holds (via the instance decl), thus:
      	d:Foo [t] t = $fFooList deq
      	deq:Eq t = ...some rhs depending on t...
      Now we add d's superclasses.  We must not then overwrite the Eq t
      constraint with a superclass selection!!
      The only decent way to solve this is to track what dependencies
      a binding has; that is what the is_loop parameter to TcSimplify.addSCs
      now does.
      Cause 2
      This shows up when simplifying the superclass context of an
      instance declaration.  Consider
        class S a
        class S a => C a where { opc :: a -> a }
        class S b => D b where { opd :: b -> b }
        instance C Int where
           opc = opd
        instance D Int where
           opd = opc
      From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int}
      Simplifying, we may well get:
      	$dfCInt = :C ds1 (opd dd)
      	dd  = $dfDInt
      	ds1 = $p1 dd
      Notice that we spot that we can extract ds1 from dd.
      Alas!  Alack! We can do the same for (instance D Int):
      	$dfDInt = :D ds2 (opc dc)
      	dc  = $dfCInt
      	ds2 = $p1 dc
      And now we've defined the superclass in terms of itself.
      Solution: treat the superclass context separately, and simplify it
      all the way down to nothing on its own.  Don't toss any 'free' parts
      out to be simplified together with other bits of context.
      This is done in TcInstDcls.tcSuperClasses, which is well commented.
      All this from a bug report from Peter White!
  5. 27 Mar, 2002 1 commit
  6. 18 Mar, 2002 1 commit
  7. 08 Mar, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-03-08 15:50:53 by simonpj] · a170160c
      simonpj authored
      	Lift the class-method type restriction
      Haskell 98 prohibits class method types to mention constraints on the
      class type variable, thus:
        class Seq s a where
          fromList :: [a] -> s a
          elem     :: Eq a => a -> s a -> Bool
      The type of 'elem' is illegal in Haskell 98, because it contains the
      constraint 'Eq a', which constrains only the class type variable (in
      this case 'a').
      This commit lifts the restriction.  The way we do that is to do a full
      context reduction (tcSimplifyCheck) step for each method separately in
      TcClassDcl.tcMethodBind, rather than doing a single context reduction
      for the whole group of method bindings.
      As a result, I had to reorganise the code a bit, and tidy up.
  8. 15 Feb, 2002 1 commit
  9. 13 Feb, 2002 1 commit
    • simonpj's avatar
      [project @ 2002-02-13 15:14:06 by simonpj] · e7030995
      simonpj authored
      	Fix a bugs in type inference for rank-N types
      We discovered this bug when looking at type rules!
      1. When type checking (e :: sigma-ty), we must specialise sigma-ty,
         else we lose the invariant that tcMonoType has.
      2. In tcExpr_id, we should pass in a Hole tyvar not an ordinary tyvar.
      As usual, I moved some functions around in consequence.
  10. 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
        - 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.
  11. 07 Feb, 2002 1 commit
  12. 05 Feb, 2002 1 commit
  13. 01 Feb, 2002 1 commit
  14. 31 Jan, 2002 1 commit
  15. 28 Dec, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-12-28 17:25:31 by simonpj] · ae969b47
      simonpj authored
      	Dealing with deriving
      I spent a ridiculously long time peering at a bug report whereby
      a 'deriving' clause sent GHC 5.02.1 into a loop.  It was all to
      do with allowing instances like
      	instance Foo a b => Baz (T a)
      (Notice the 'b' on the left which does not appear on the right.)
      I realised that it's hard for the deriving machinery to find a
      fixpoint when these sort of instance decls are around.  So I
      now constrain *derived* instance decls not to have this form;
      all the tyvars on the left must appear on the right.
      On the way I commoned up the previously-separate tcSimplify
      machinery for 'deriving' and 'default' decls with that for
      everything else.   As a result, quite a few files are touched.
      I hope I havn't broken anything.
  16. 20 Dec, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-12-20 11:19:05 by simonpj] · 91c750cb
      simonpj authored
      	More type system extensions (for John Hughes)
      1.  Added a brand-new extension that lets you derive ARBITRARY CLASSES
      for newtypes.  Thus
      	newtype Age = Age Int deriving( Eq, Ord, Shape, Ix )
      The idea is that the dictionary for the user-defined class Shape Age
      is *identical* to that for Shape Int, so there is really no deriving
      work to do.   This saves you writing the very tiresome instance decl:
      	instance Shape Age where
      	   shape_op1 (Age x) = shape_op1 x
      	   shape_op2 (Age x1) (Age x2) = shape_op2 x1 x2
      It's more efficient, too, becuase the Shape Age dictionary really
      will be identical to the Shape Int dictionary.
      There's an exception for Read and Show, because the derived instance
      *isn't* the same.
      There is a complication where higher order stuff is involved.  Here is
      the example John gave:
         class StateMonad s m | m -> s where ...
         newtype Parser tok m a = Parser (State [tok] (Failure m) a)
      			  deriving( Monad, StateMonad )
      Then we want the derived instance decls to be
         instance Monad (State [tok] (Failure m)) => Monad (Parser tok m)
         instance StateMonad [tok] (State [tok] (Failure m))
      	 => StateMonad [tok] (Parser tok m)
      John is writing up manual entry for all of this, but this commit
      implements it.   I think.
      2.  Added -fallow-incoherent-instances, and documented it.  The idea
      is that sometimes GHC is over-protective about not committing to a
      particular instance, and the programmer may want to say "commit anyway".
      Here's the example:
          class Sat a where
            dict :: a
          data EqD a = EqD {eq :: a->a->Bool}
          instance Sat (EqD a) => Eq a where
            (==) = eq dict
          instance Sat (EqD Integer) where
            dict = EqD{eq=(==)}
          instance Eq a => Sat (EqD a) where
            dict = EqD{eq=(==)}
          class Collection c cxt | c -> cxt where
            empty :: Sat (cxt a) => c a
            single :: Sat (cxt a) => a -> c a
            union :: Sat (cxt a) => c a -> c a -> c a
            member :: Sat (cxt a) => a -> c a -> Bool
          instance Collection [] EqD where
            empty = []
            single x = [x]
            union = (++)
            member = elem
      It's an updated attempt to model "Restricted Data Types", if you
      remember my Haskell workshop paper. In the end, though, GHC rejects
      the program (even with fallow-overlapping-instances and
      fallow-undecideable-instances), because there's more than one way to
      construct the Eq instance needed by elem.
      Yet all the ways are equivalent! So GHC is being a bit over-protective
      of me, really: I know what I'm doing and I would LIKE it to pick an
      arbitrary one. Maybe a flag fallow-incoherent-instances would be a
      useful thing to add?
  17. 29 Nov, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-11-29 13:47:09 by simonpj] · 32a89583
      simonpj authored
      	Add linear implicit parameters
      Linear implicit parameters are an idea developed by Koen Claessen,
      Mark Shields, and Simon PJ, last week.  They address the long-standing
      problem that monads seem over-kill for certain sorts of problem, notably:
      	* distributing a supply of unique names
      	* distributing a suppply of random numbers
      	* distributing an oracle (as in QuickCheck)
      Linear implicit parameters are just like ordinary implicit parameters,
      except that they are "linear" -- that is, they cannot be copied, and
      must be explicitly "split" instead.  Linear implicit parameters are
      written '%x' instead of '?x'.  (The '/' in the '%' suggests the
      For example:
          data NameSupply = ...
          splitNS :: NameSupply -> (NameSupply, NameSupply)
          newName :: NameSupply -> Name
          instance PrelSplit.Splittable NameSupply where
      	split = splitNS
          f :: (%ns :: NameSupply) => Env -> Expr -> Expr
          f env (Lam x e) = Lam x' (f env e)
      		      x'   = newName %ns
      		      env' = extend env x x'
          ...more equations for f...
      Notice that the implicit parameter %ns is consumed
      	once by the call to newName
      	once by the recursive call to f
      So the translation done by the type checker makes
      the parameter explicit:
          f :: NameSupply -> Env -> Expr -> Expr
          f ns env (Lam x e) = Lam x' (f ns1 env e)
      	 		 (ns1,ns2) = splitNS ns
      			 x' = newName ns2
      			 env = extend env x x'
      Notice the call to 'split' introduced by the type checker.
      How did it know to use 'splitNS'?  Because what it really did
      was to introduce a call to the overloaded function 'split',
      ndefined by
      	class Splittable a where
      	  split :: a -> (a,a)
      The instance for Splittable NameSupply tells GHC how to implement
      split for name supplies.  But we can simply write
      	g x = (x, %ns, %ns)
      and GHC will infer
      	g :: (Splittable a, %ns :: a) => b -> (b,a,a)
      The Splittable class is built into GHC.  It's defined in PrelSplit,
      and exported by GlaExts.
      Other points:
      * '?x' and '%x' are entirely distinct implicit parameters: you
        can use them together and they won't intefere with each other.
      * You can bind linear implicit parameters in 'with' clauses.
      * You cannot have implicit parameters (whether linear or not)
        in the context of a class or instance declaration.
      The monomorphism restriction is even more important than usual.
      Consider the example above:
          f :: (%ns :: NameSupply) => Env -> Expr -> Expr
          f env (Lam x e) = Lam x' (f env e)
      		      x'   = newName %ns
      		      env' = extend env x x'
      If we replaced the two occurrences of x' by (newName %ns), which is
      usually a harmless thing to do, we get:
          f :: (%ns :: NameSupply) => Env -> Expr -> Expr
          f env (Lam x e) = Lam (newName %ns) (f env e)
      		      env' = extend env x (newName %ns)
      But now the name supply is consumed in *three* places
      (the two calls to newName,and the recursive call to f), so
      the result is utterly different.  Urk!  We don't even have
      the beta rule.
      Well, this is an experimental change.  With implicit
      parameters we have already lost beta reduction anyway, and
      (as John Launchbury puts it) we can't sensibly reason about
      Haskell programs without knowing their typing.
      Of course, none of this is throughly tested, either.
  18. 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
      	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
      	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
      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
      All of this doesn't come entirely for free.  Here's the typechecker
      line count (INCLUDING comments)
      	Before	16,551
      	After	17,116
  19. 31 Oct, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-10-31 15:22:53 by simonpj] · 61bfd5dd
      simonpj authored
      	Improved handling of scoped type variables
      The main effect of this commit is to allow scoped type variables
      in pattern bindings, thus
      	(x::a, y::b) = e
      This was illegal, but now it's ok.  a and b have the same scope
      as x and y.
      On the way I beefed up the info inside a type variable
      (TcType.TyVarDetails; c.f. IdInfo.GlobalIdDetails) which
      helps to improve error messages. Hence the wide ranging changes.
      Pity about the extra loop from Var to TcType, but can't be helped.
  20. 25 Oct, 2001 2 commits
    • simonpj's avatar
      [project @ 2001-10-25 14:30:43 by simonpj] · d5f94cc1
      simonpj authored
        Correct an error in the handling of implicit parameters
      Mark Shields discovered a bug in the way that implicit parameters
      are dealt with by the type checker.  It's all a bit subtle, and
      is extensively documented in TcSimplify.lhs.
      This commit makes the code both simpler and more correct.  It subtly
      changes the way in which type signatures are treated, but not in a way
      anyone would notice: see notes with "Question 2: type signatures"
      in TcSimplify.lhs.
    • simonpj's avatar
      [project @ 2001-10-25 09:58:39 by simonpj] · 2007c7e6
      simonpj authored
  21. 17 Oct, 2001 1 commit
  22. 28 Aug, 2001 1 commit
  23. 20 Aug, 2001 1 commit
  24. 25 Jul, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-07-25 15:55:30 by simonpj] · 7fde87b3
      simonpj authored
      	Fix a bug in the monomorphism restriction
      Thanks for Koen for reporting this bug.
      In tcSimplifyRestricted, I wrongly called tcSimpifyToDicts,
      whereas actually we have to simplfy further than simply to
      a dictionary.
      The test for this is in typecheck/should_compile/tc132.hs
  25. 23 Jul, 2001 1 commit
  26. 17 Jul, 2001 1 commit
  27. 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
  28. 25 Jun, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-06-25 08:01:16 by simonpj] · a12bed53
      simonpj authored
      	Fix a predicate-simplification bug
      Fixes a bug pointed out by Marcin
          data R = R {f :: Int}
          foo:: (?x :: Int) => R -> R
          foo r = r {f = ?x}
      	Could not deduce `?x :: Int' from the context ()
      	arising from use of implicit parameter `?x' at Test.hs:4
      	In the record update: r {f = ?x}
      	In the definition of `foo': r {f = ?x}
      The predicate simplifier was declining to 'inherit' an
      implicit parameter.  This is right for a let-binding, but
      wrong for an expression binding.  For example, a simple
      expression type signature:
      		(?x + 1) :: Int
      This was rejected because the ?x constraint could not be
      floated out -- but that's wrong for expressions.
  29. 03 May, 2001 3 commits
    • simonpj's avatar
      [project @ 2001-05-03 12:33:50 by simonpj] · bbc670f4
      simonpj authored
      ****	MERGE WITH 5.00 BRANCH     ********
      	Monomorphism restriction for implicit parameters
      This commit tidies up the way in which monomorphic bindings
      are dealt with, incidentally fixing a bug to do with implicit
      The tradeoffs concerning monomorphism and implicit paramters are
      now documented in TcSimplify.lhs, and all the strategic choices
      are made there (rather than in TcBinds where they were before).
      I've continued with choice (B) -- which Jeff first implemented --
      because that's what Hugs does, lacking any other consensus.
    • simonpj's avatar
      [project @ 2001-05-03 09:32:48 by simonpj] · b473b6c2
      simonpj authored
      	Dramatically improve the error messages arising
      	from failed unifications triggered by 'improvement'
      A bit more plumbing in FunDeps, and consequential wibbles elsewhere
      Changes this:
          Couldn't match `Int' against `[(String, Int)]'
      	Expected type: Int
      	Inferred type: [(String, Int)]
      to this:
      	Couldn't match `Int' against `[(String, Int)]'
      	    Expected type: Int
      	    Inferred type: [(String, Int)]
      	When using functional dependencies to combine
      	  ?env :: Int, arising from a type signature at Foo.hs:7
      	  ?env :: [(String, Int)],
      	    arising from use of implicit parameter `?env' at Foo.hs:8
      	When generalising the types for ident
    • simonpj's avatar
      [project @ 2001-05-03 08:13:25 by simonpj] · cd7dc9b1
      simonpj authored
      ****	MERGE WITH 5.00 BRANCH     ********
      	Fix a bad implicit parameter bug
      TcSimplify.tcSimplifyIPs was just completely wrong; it wasn't
      doing improvement properly nor binding values properly. Sigh.
      To make this work nicely I added
      	Inst.instName :: Inst -> Name
  30. 30 Apr, 2001 1 commit
  31. 12 Apr, 2001 1 commit
    • lewie's avatar
      [project @ 2001-04-12 21:29:43 by lewie] · ebf2c802
      lewie authored
      Don't use the same simplify code for both restricted and unrestricted
      bindings.  In particular, a restricted binding shouldn't try to capture
      implicit params.
  32. 05 Apr, 2001 1 commit
  33. 13 Mar, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-03-13 14:58:25 by simonpj] · 788faebb
      simonpj authored
      	Nuke ClassContext
      This commit tidies up a long-standing inconsistency in GHC.
      The context of a class or instance decl used to be restricted
      to predicates of the form
      	C t1 .. tn
      	type ClassContext = [(Class,[Type])]
      but everywhere else in the compiler we used
      	type ThetaType = [PredType]
      where PredType can be any sort of constraint (= predicate).
      The inconsistency actually led to a crash, when compiling
      	class (?x::Int) => C a where {}
      I've tidied all this up by nuking ClassContext altogether, and using
      PredType throughout.  Lots of modified files, but all in
      more-or-less trivial ways.
      I've also added a check that the context of a class or instance
      decl doesn't include a non-inheritable predicate like (?x::Int).
      Other things
       * rename constructor 'Class' from type TypeRep.Pred to 'ClassP'
         (makes it easier to grep for)
       * rename constructor HsPClass  => HsClassP
      		      HsPIParam => HsIParam
  34. 28 Feb, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-02-28 17:17:55 by simonpj] · 56d75e0b
      simonpj authored
      Improve rule matching
      When doing constraint simplification on the LHS of a rule,
      we *don't* want to do superclass commoning up.  Consider
      	fromIntegral :: (Integral a, Num b) => a -> b
      	{-# RULES "foo"  fromIntegral = id :: Int -> Int #-}
      Here, a=b=Int, and Num Int is a superclass of Integral Int. But we *dont*
      want to get
      	forall dIntegralInt.
      	fromIntegral Int Int dIntegralInt (scsel dIntegralInt) = id Int
      because the scsel (super class selection) will mess up matching.
      Instead we want
      	forall dIntegralInt, dNumInt.
      	fromIntegral Int Int dIntegralInt dNumInt = id Int
      TcSimplify.tcSimplifyToDicts is the relevant function, but I had
      to generalise the main simplification loop a little (adding the
      type WantSCs).
  35. 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.
  36. 20 Feb, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-02-20 09:42:50 by simonpj] · 22ffc06a
      simonpj authored
      Typechecking [TcModule, TcBinds, TcHsSyn, TcInstDcls, TcSimplify]
      * Fix a bug in TcSimplify that broke functional dependencies.
        Interleaving unification and context reduction is trickier 
        than I thought.  Comments in the code amplify.  
      * Fix a functional-dependency bug, that meant that this pgm:
      	class C a b | a -> b where f :: a -> b
      	g :: (C a b, Eq b) => a -> Bool
      	g x = f x == f x
        gave an ambiguity error report.  I'm afraid I've forgotten
        what the problem was.
      * Correct the implementation of the monomorphism restriction,
        in TcBinds.generalise.  This fixes Marcin's bug report:
      	test1 :: Eq a => a -> b -> b
      	test1 x y = y
      	test2 = test1 (3::Int)
        Previously we were erroneously inferring test2 :: () -> ()
      * Make the "unf_env" that is looped round in TcModule go round
        in a big loop, not just round tcImports.  This matters when
        we have mutually recursive modules, so that the Ids bound in
        the source code may appear in the imports.  Sigh.  But no big
        It does mean that you have to be careful not to call isLocalId,
        isDataConId etc, because they consult the IdInfo of an Id, which 
        in turn may be determined by the loop-tied unf_env.
  37. 30 Jan, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-01-30 09:53:11 by simonpj] · ade2eac4
      simonpj authored
      More on functional dependencies
      My last commit allowed this:
      	instance C a b => C [a] [b] where ...
      if we have
      	class C a b | a -> b
      This commit completes the change, by making the 
      improvement stages improve only the 'shape' of the second
      argument of C.  
      I also had to change the iteration in TcSimplify -- see
      the comments in TcSimplify.inferLoop.