[r6rs-discuss] Now, where were we?
William D Clinger
will at ccs.neu.edu
Mon Feb 23 10:07:54 EST 2009
Sam TH quoting Andrew Reilly:
> > What I don't understand is why having some nicely defined
> > meaning for "finished" programs should preclude a useful
> > semantics for "work-in-progress" programs (REPL). Can't we have
> > both? Please?
> The trouble is that it's hard to give them consistent semantics.
No, it isn't hard. For example, IEEE Standard 1178-1990
defines a semantics that can be implemented consistently
for both "finished" programs and REPLs.
The R6RS semantics, as I have repeatedly pointed out and
as Sam's example also demonstrates, is incompatible with
REPLs. Sam's example points out that the R6RS semantics
for macro expansion requires two separate passes over a
top-level program or library. The R6RS did not have to
require a two-pass algorithm, but that's what it did.
Hence the problem.
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