• 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
      (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.
HscTypes.lhs 81 KB