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    • simonpj@microsoft.com's avatar
      Make record selectors into ordinary functions · 9ffadf21
      simonpj@microsoft.com authored
      This biggish patch addresses Trac #2670.  The main effect is to make
      record selectors into ordinary functions, whose unfoldings appear in
      interface files, in contrast to their previous existence as magic
      "implicit Ids".  This means that the usual machinery of optimisation,
      analysis, and inlining applies to them, which was failing before when
      the selector was somewhat complicated.  (Which it can be when
      strictness annotations, unboxing annotations, and GADTs are involved.)
      
      The change involves the following points
      
      * Changes in Var.lhs to the representation of Var.  Now a LocalId can
        have an IdDetails as well as a GlobalId.  In particular, the
        information that an Id is a record selector is kept in the
        IdDetails.  While compiling the current module, the record selector
        *must* be a LocalId, so that it participates properly in compilation
        (free variables etc).
      
        This led me to change the (hidden) representation of Var, so that there
        is now only one constructor for Id, not two.
      
      * The IdDetails is persisted into interface files, so that an
        importing module can see which Ids are records selectors.
      
      * In TcTyClDecls, we generate the record-selector bindings in renamed,
        but not typechecked form.  In this way, we can get the typechecker
        to add all the types and so on, which is jolly helpful especially
        when GADTs or type families are involved.  Just like derived
        instance declarations.
      
        This is the big new chunk of 180 lines of code (much of which is
        commentary).  A call to the same function, mkAuxBinds, is needed in
        TcInstDcls for associated types.
      
      * The typechecker therefore has to pin the correct IdDetails on to 
        the record selector, when it typechecks it.  There was a neat way
        to do this, by adding a new sort of signature to HsBinds.Sig, namely
        IdSig.  This contains an Id (with the correct Name, Type, and IdDetails);
        the type checker uses it as the binder for the final binding.  This
        worked out rather easily.
      
      * Record selectors are no longer "implicit ids", which entails changes to
           IfaceSyn.ifaceDeclSubBndrs
           HscTypes.implicitTyThings
           TidyPgm.getImplicitBinds
        (These three functions must agree.)
      
      * MkId.mkRecordSelectorId is deleted entirely, some 300+ lines (incl
        comments) of very error prone code.  Happy days.
      
      * A TyCon no longer contains the list of record selectors: 
        algTcSelIds is gone
      
      The renamer is unaffected, including the way that import and export of
      record selectors is handled.
      
      Other small things
      
      * IfaceSyn.ifaceDeclSubBndrs had a fragile test for whether a data
        constructor had a wrapper.  I've replaced that with an explicit flag
        in the interface file. More robust I hope.
      
      * I renamed isIdVar to isId, which touched a few otherwise-unrelated files.
      
      9ffadf21
  21. 31 Dec, 2008 1 commit