[MLton] mlb support

[Matthew Fluet]

I've got mlbs working to the point where pretty much everything except for
the def-use controls is working.  Currently, the annotation language looks
like:

ann := allowConstant {true|false}   defaults to false
     | allowExport {true|false}     defaults to true
     | allowImport {true|false}     defaults to true
     | allowOverload {true|false}   defaults to false
     | allowPrim {true|false}       defaults to false
     | deadCode {true|false}        defaults to false
     | rebindEquals {true|false}    defaults to false
     | sequenceUnit {true|false}    defaults to !Control.sequenceUnit
     | warnMatch {true|false}       defaults to
                                    (!Control.warnNonExhaustive
                                     orelse !Control.warnRedundant)

The defaults are reset for each .mlb file.

Is there a reason that warnMatch is split into the two controls?
I haven't gotten rid of the !Control.warnNonExhaustive or
!Control.warnRedundant predicates in defunctorize.fun.  This means that
even if you annotate with  warnMatch true  , you won't get the warnings
unless you compile with -warnMatch true.  That kind of goes against what
we wanted, but if I drop the predicates, then the only use of those
controls will be to default the warnMatch annotation, and I can't see
keeping two of them around for that purpose.

I think I've simplified the handling of -build-constants.  Rather than
sucking in the entire Basis Library, -build-constants just elaborates
  $(SML_BASIS)/libs/primitive.mlb
whose contents look like:

  _prim

  ann
    allowConstant true,
    allowPrim true,
    rebindEquals true,
    deadCode true
  in
    ../misc/primitive.sml
    ../posix/primitive.sml
  end

Then, build.mlb looks like
  ann  deadCode true  in
  primitive.mlb
  ../top-level/infixes.sml
  ...
  end
and it makes it clear that no other extensions are needed for the
remainder of the Basis Library.  (Another use of rebindEquals and
a use of allowOverload are needed in basis-2002.mlb.)

Right now "$(SML_BASIS)/libs/primitive.mlb" is hard-wired into the
compiler.  I guess it's no worse than basis-library/libs/build having been
hard-wired in before.

One question is where to make SML_BASIS actually point.  Recall that the
directory structure for the basis-library looks like:

basis-library/libs/build
                  /basis-2002/bind
                  /basis-1997/bind
                  /basis-none/bind

That was fine for before, but I don't want to write:
  $(SML_BASIS)/libs/basis-2002/basis-2002.mlb

I'd rather write:
  $(SML_BASIS)/basis.mlb
  $(SML_BASIS)/basis-2002.mlb
  $(SML_BASIS)/basis-1997.mlb
  $(SML_BASIS)/basis-none.mlb

so I'm thinking of pointing SML_BASIS to basis-library/libs.


As a consequence of this rearrangement, the SML/NJ compiled version of
MLton doesn't pull in the Basis Library.  Means that things will be a
little slower, but they were going to be anyways, because expanding a
single z.sml file to
  local $(SML_BASIS)/basis-2002.mlb in z.sml end
meant sucking in the basis at compile time.


Those are the major points.  I'm still trying to figure out how best to
handle the def-use information.  I at least want a coherent story for
dealing with warnUnused, because it is fairly useful.