[MLton] can mlbasis rename the top-level?

[Matthew Fluet]

> Using the MLB files to rename structures is very useful.
> However, what about things at the top-level?

Structures are at the top-level.  But, no, there is no means to rename 
Core language bindings at the tope-level.  You can always drop down into a 
.sml file to do so.  Likewise, you can't open a structure in an MLB file, 
you need to drop down to .sml.

At this point, Stephen usually chimes in and says how useful it would be 
allow raw SML in a MLB file, with the obvious semantics.  And, I'm 
becoming more and more convinced of the utility of this.  I think some 
sort of "escape" mechanism, like in MLYacc for dentoting semantic actions 
or "here documents" in bash, would be useful:

local
   $(SML_LIB)/basis/basis.mlb
   $(SML_LIB)/smlnj-lib/Util/smlnj-lib.mlb
in
{{{
   structure IntRedBlackMap = RedBlackMapFn(type ord_key = int
                                            val compare = Int.compare)
}}}
end

I like the idea of delimiting the the sml in a manner that doesn't require 
embedding the SML grammar in the MLB grammar.  I imagine something like 
the above could be handled by the lexer, yielding a (big) string token, 
which could be pushed through the SML lexer/parser rather than a file 
name.

> If a library exports '$' at the top-level, can I move it?
> I mean something  like:
>
> local
>  libdemo.mlb (* exports $ at the top-level *)
> in
>  structure Demo = *
>  mycode.sml (* expects $ placed in Demo.$ *)
> end
>
> I want all of the top-level stuff defined in libdemo.mlb put
> inside a single structure, out of my top-level namespace.

Bear in mind, that the top-level basis includes type, value (including 
datatype constructors and exception constructors), structures, signatures, 
and functors.  Signatures and functors may not be reified into a 
structure.  So, it is a bit more complicated to extract the portion of the 
basis that is acceptable in a signature.

> This is the sort of problem I thought MLB files solve, but I
> can't figure out how to do this from the documentation.

It isn't possible with the syntax and semantics currently available.  And, 
I'm not convinced that you shouldn't be doing:

local
   local
     libdemob.mlb
   in
     mydemo.sml
   end
in
   mycode.sml
end

where mydemo.sml explicitly rebinds the portion of libdemob.mlb that you 
wish available through structure Demo.