1. 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.
  2. 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?
  3. 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.
  4. 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
  5. 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.
  6. 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
  7. 17 Oct, 2001 1 commit
  8. 28 Aug, 2001 1 commit
  9. 20 Aug, 2001 1 commit
  10. 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
  11. 23 Jul, 2001 1 commit
  12. 17 Jul, 2001 1 commit
  13. 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
  14. 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.
  15. 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
  16. 30 Apr, 2001 1 commit
  17. 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.
  18. 05 Apr, 2001 1 commit
  19. 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
  20. 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).
  21. 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.
  22. 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.
  23. 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.
  24. 29 Jan, 2001 1 commit
  25. 26 Jan, 2001 1 commit
  26. 25 Jan, 2001 1 commit
    • simonpj's avatar
      [project @ 2001-01-25 17:54:24 by simonpj] · 4e342297
      simonpj authored
      	   Mainly FunDeps (23 Jan 01)
      This commit re-engineers the handling of functional dependencies.
      A functional dependency is no longer an Inst; instead, the necessary
      dependencies are snaffled out of their Class when necessary.
      As part of this exercise I found that I had to re-work how to do generalisation
      in a binding group.  There is rather exhaustive documentation on the new Plan
      at the top of TcSimplify.
      	WARNING: I have compiled all the libraries with this new compiler
      		 and all looks well, but I have not run many programs.
      		 Things may break.  Let me know if so.
      The main changes are these:
      1.  typecheck/TcBinds and TcSimplify have a lot of changes due to the
          new generalisation and context reduction story.  There are extensive
          comments at the start of TcSimplify
      2.  typecheck/TcImprove is removed altogether.  Instead, improvement is
          interleaved with context reduction (until a fixpoint is reached).
          All this is done in TcSimplify.
      3.  types/FunDeps has new exports
      	* 'improve' does improvement, returning a list of equations
      	* 'grow' and 'oclose' close a list of type variables wrt a set of
      	  PredTypes, but in slightly different ways.  Comments in file.
      4.  I improved the way in which we check that main::IO t.  It's tidier now.
      In addition
      *   typecheck/TcMatches:
      	a) Tidy up, introducing a common function tcCheckExistentialPat
      	b) Improve the typechecking of parallel list comprehensions,
      	   which wasn't quite right before.  (see comments with tcStmts)
      	WARNING: (b) is untested!  Jeff, you might want to check.
      *   Numerous other incidental changes in the typechecker
      *   Manuel found that rules don't fire well when you have partial applications
          from overloading.  For example, we may get
      	f a (d::Ord a) = let m_g = g a d
      			 \y :: a -> ...(m_g (h y))...
          The 'method' m_g doesn't get inlined because (g a d) might be a redex.
          Yet a rule that looks like
      		g a d (h y) = ...
          won't fire because that doesn't show up.  One way out would be to make
          the rule matcher a bit less paranoid about duplicating work, but instead
          I've added a flag
          which controls whether we generate things like m_g in the first place.
          It's not clear that they are a win in the first place.
          The flag is actually consulted in Inst.tcInstId
  27. 03 Jan, 2001 1 commit
  28. 14 Nov, 2000 1 commit
  29. 13 Nov, 2000 1 commit
  30. 10 Nov, 2000 1 commit
    • simonpj's avatar
      [project @ 2000-11-10 15:12:50 by simonpj] · f23ba2b2
      simonpj authored
      1.	Outputable.PprStyle now carries a bit more information
      	In particular, the printing style tells whether to print
      	a name in unqualified form.  This used to be embedded in
      	a Name, but since Names now outlive a single compilation unit,
      	that's no longer appropriate.
      	So now the print-unqualified predicate is passed in the printing
      	style, not embedded in the Name.
         2.	I tidied up HscMain a little.  Many of the showPass messages
      	have migraged into the repective pass drivers
  31. 23 Oct, 2000 1 commit
  32. 17 Oct, 2000 1 commit
  33. 16 Oct, 2000 1 commit
  34. 12 Oct, 2000 1 commit
  35. 03 Oct, 2000 1 commit
    • simonpj's avatar
      [project @ 2000-10-03 08:43:00 by simonpj] · 710e2074
      simonpj authored
      	Adding generics		SLPJ Oct 2000
      This big commit adds Hinze/PJ-style generic class definitions, based
      on work by Andrei Serjantov.  For example:
        class Bin a where
          toBin   :: a -> [Int]
          fromBin :: [Int] -> (a, [Int])
          toBin {| Unit |}    Unit	  = []
          toBin {| a :+: b |} (Inl x)   = 0 : toBin x
          toBin {| a :+: b |} (Inr y)   = 1 : toBin y
          toBin {| a :*: b |} (x :*: y) = toBin x ++ toBin y
          fromBin {| Unit |}    bs      = (Unit, bs)
          fromBin {| a :+: b |} (0:bs)  = (Inl x, bs')    where (x,bs') = fromBin bs
          fromBin {| a :+: b |} (1:bs)  = (Inr y, bs')    where (y,bs') = fromBin bs
          fromBin {| a :*: b |} bs  	  = (x :*: y, bs'') where (x,bs' ) = fromBin bs
      							  (y,bs'') = fromBin bs'
      Now we can say simply
        instance Bin a => Bin [a]
      and the compiler will derive the appropriate code automatically.
      		(About 9k lines of diffs.  Ha!)
      Generic related things
      * basicTypes/BasicTypes: The EP type (embedding-projection pairs)
      * types/TyCon:
      	An extra field in an algebraic tycon (genInfo)
      * types/Class, and hsSyn/HsBinds:
      	Each class op (or ClassOpSig) carries information about whether
      	it  	a) has no default method
      		b) has a polymorphic default method
      		c) has a generic default method
      	There's a new data type for this: Class.DefMeth
      * types/Generics:
      	A new module containing good chunk of the generic-related code
      	It has a .hi-boot file (alas).
      * typecheck/TcInstDcls, typecheck/TcClassDcl:
      	Most of the rest of the generics-related code
      * hsSyn/HsTypes:
      	New infix type form to allow types of the form
      		data a :+: b = Inl a | Inr b
      * parser/Parser.y, Lex.lhs, rename/ParseIface.y:
      	Deal with the new syntax
      * prelude/TysPrim, TysWiredIn:
      	Need to generate generic stuff for the wired-in TyCons
      * rename/RnSource RnBinds:
      	A rather gruesome hack to deal with scoping of type variables
      	from a generic patterns.  Details commented in the ClassDecl
      	case of RnSource.rnDecl.
      	Of course, there are many minor renamer consequences of the
      	other changes above.
      * lib/std/PrelBase.lhs
      	Data type declarations for Unit, :+:, :*:
      Slightly unrelated housekeeping
      * hsSyn/HsDecls:
      	ClassDecls now carry the Names for their implied declarations
      	(superclass selectors, tycon, etc) in a list, rather than
      	laid out one by one.  This simplifies code between the parser
      	and the type checker.
      * prelude/PrelNames, TysWiredIn:
      	All the RdrNames are now together in PrelNames.
      * utils/ListSetOps:
      	Add finite mappings based on equality and association lists (Assoc a b)
      	Move stuff from List.lhs that is related
  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
  37. 14 Jul, 2000 1 commit
    • lewie's avatar
      [project @ 2000-07-14 23:54:06 by lewie] · f6d9b940
      lewie authored
      Functional Dependencies were not getting simplified away when the dictionary
      that generated them was simplified by instance resolution.  Fixed.