At Mon, 18 Mar 2019 19:32:40 -0400, Philip McGrath wrote:
> On Mon, Mar 18, 2019 at 9:14 AM Matthew Flatt <mfl...@cs.utah.edu> wrote:
>
> > I wonder whether the solution is an extension of `scribble/lp2` to
> > support a `require-for-chunk` form where `chunk` records any such
> > imports in its context and adds then to the stitched-together program.
> >
> > (require-for-chunk (only-in racket/string string-join))
> >
> > (define-syntax-parser cross-phase-macro
> > [(_ <>:id)
> > @#`begin{@(func-not-exported)
> >
> > @chunk[<>
> > (string-join ....
> >
> > would work because `chunk` would pick up the `(only-in racket/string
> > string-join)` from its context and attach it to the chunk, so that
> > `(only-in racket/string string-join)` would be added to the
> > stitched-together context.
> >
> > Maybe this would work by having `require-for-chunk` expand to something
> > like `(begin-for-syntax (register-require #'chunk ....))` to register
> > in a compile-time free-id table mapping from the #'chunk identifier to
> > a list of imports. Then, the `chunk` macro would consult the table
> > using the identifier that invoked the macro. (I have not tried this to
> > be sure that it would work.)
> >
>
> While thinking about this idea, I came up with a simpler example that
> exposes a hygiene issue in `scribble/lp2` without using `require`:
>
> #lang scribble/lp2
> @(define-syntax-rule (chunk/define <> lhs rhs ...)
> (chunk <>
> (define hygiene "this shouldn't cause capture")
> (define lhs rhs ...)))
> @(chunk <*> <a> <b>)
> @(chunk/define <a> a 1)
> @(chunk/define <b> b 2)
>
> fails with the error "module: identifier already defined in: hygiene".
I can see why you might want this, but for what it's worth, I can also
see an argument against for `scribble/lp2`. If it did work, the typeset
output would be
<*> ::=
<a>
<b>
<a> ::=
(define hygiene "this shouldn't cause capture")
(define a 1)
<b> ::=
(define hygiene "this shouldn't cause capture")
(define b 2)
which seems like nonsense. That is, there's not an extra dimension to
represent the macro-introduced scope in the textual output output, so
maybe it shouldn't be allowed.
Probably it's possible to make this work using delta introducers to
manipulate scopes, though.
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