Joe Marshall wrote: > So am I right in assuming that you were thinking of FEXPRs in the > general case rather than the way SCM uses the term?
SCM fexprs can't (in general) be expanded until run-time so I'm not sure what you are asking. Hobbit (the compiler that come's with SCM) compiles only a subset of programs, as far as I recall. Actually, it's useful that SCM's fexprs have this property: it makes it possible to write domain-specific incremental (re-)compilers in Scheme. Fexprs just add a new rule to application: if the first position of an application points to a fexpr, arguments are unevaluated but the result an expression which is itself evaluated. I'd like fexprs in combination with first-class environments which are reified if and only if their lexical scope includes a call "(the-environment)". Those features should be optional because they can be expensive to implement yet they are hardly ever directly needed. They should be spelled out because they are a trivial, obvious, and useful generalization of the basic operational model of Scheme. They're useful, in part, because things like PLT-style modules or modern macro systems can be expressed cleanly in terms of fexprs and environments, and in ways in which the fexprs and environments naturally "fall out" from the code after a little partial evaluation. At the same time, those very same implementations that a compiler can eliminate by partial reduction, are pragmatically useful in interpreters. So, if R6 added little more than optional fexprs and environments, quite a lot else that's big, new and complicated in R6 could be implemented, portably, albeit on optional features. Implementations could, as they do now, skip the optional features and use custom implementations of *SRFIs* like a module system. -t > > On 5/27/07, Thomas Lord <[EMAIL PROTECTED]> wrote: >> Thomas Lord wrote: >> > In the *general case* you can't expand fexpr-style macros at >> > run-time however >> >> ur... that's "until" run-time, not "at," of course. >> >> -t >> >> > > _______________________________________________ r6rs-discuss mailing list r6rs-discuss@lists.r6rs.org http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
