On Wed, 4 Apr 2007, Andreas Rossberg wrote:
> I'm afraid it is - Compiler.evalWith is as close as you can get. The
> reason is not so much lack of dynamism, but the non-priviledged status
> and functional purity of compiler and toplevel in the Alice system.
> The interactive toplevel is even less magic. It is an ordinary
> application, written all in plain ML, on top of the Compiler structure.
> Roughly, all it does is running an interactive loop invoking
> Compiler.evalWith and threading the environment (plus a few other
> things, e.g. installing its own component manager to enable the reset
> functionality). Thus the "current" environment can only be updated after
> complete processing of an input, not in-between. IOW, all input has to
> be sequentialised - that is what the "use" queue accomplishes.
This sounds like we should get along with Compile.evalWith, while updating
a global env ref stored in our own toplevel environment. (Isabelle
provides a separate read-eval-print loop, but needs to be able to eval
arbitrary ML code occasionally, without leaving that loop.)
A remaining hindrance appears to be the slightly strict handling of a
sequence of toplevel ML declarations in Alice. This problem can already
be reproduced with the 'use' provided by the Alice toplevel. For example:
Alice> val a = 1; val b = a + 1; (* works *)
File a.ML: val a = 1
Alice> use "a.ML"; val b = a + 1; (* fails, unknown `a' *)
Alice> use "a.ML"; \n val b = a + 1; (* works *)
The second version fails, because the whole line is compiled before the
content of a.ML is evaluated. The third version works again, because the
read-eval-print loop happens to treat separate lines of input as units for
sequential evaluation (cf. tools/toplevel/TextToplevel.aml).
As far as I understand other ML toplevels (notably Poly/ML), the outermost
loop takes care not to read chunks of declarations too eagerly. Thus the
natural sequential division of toplevel declarations is maintained. E.g.
decl1; decl2 is processed as
compile(decl1); exec(decl1); compile(decl2); exec(decl2)
instead of
compile(decl1); compile(decl2); exec(decl1); exec(decl2)
performed in Alice, as it seems. The same problem is encountered, when
'use' occurs recursively within the used file.
Is there a chance to get the former kind of seqential Compile.evalWith in
Alice? Or maybe just a parser function to split a string consisting of
several ML declarations into a list of strings?
Makarius
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