I'm working on a REPL for a #lang in which one can make definitions. One writes
$x := 5 and this gets parsed into an S-expression like (assignment "x" 5) The #lang is not based on S-expressions, but I believe that that's irrelevant (though I may be wrong). Naturally enough, I've set up the expander for my #lang so that S-expressions like the previous one get elaborated into a plain Racket define: (define x 5) The #lang works in DrRacket, and at the command line, too. The difficulty is the REPL, which is based on the same expander but a slightly modified reader. The problem shows up when one writes > $x := 5 in the REPL. There, I get define: not allowed in an expression context This makes sense to me because what's actually being evaluated in the REPL setting is (#%top-interaction assignment "a" 1) The define to which the assignment S-expression elaborates does indeed seem to be in an expression context. (Or, at least, it's not toplevel; the #%top-interaction makes sure of that.) Is there any way around this? Not being able to assign values to variables in the REPL is a blocker for me. I see a few options on the table for this issue: * Tweak current-eval (used by read-eval-print-loop). Doing this might open the door to bypassing #%top-interaction. What would that look like? Would one just destructure the given form to eval, checking whether it looks like a #%top-interaction, in which case throw it away and hand the rest to the "real" eval? * Change what assignment means. Thus, (assignment "a" 5) would no longer expand to (define a 5), but to something else, e.g., a set! or box-set! that modifies an environment that I maintain by hand. * Roll my own poor man's read-eval-print-loop. Of course, then I'd truly be in the driver's seat, but that option would clearly be a duplication of work the read-eval-print-loop is doing, and I really don't want to do that. Perhaps I'm missing something here. Any suggestions? -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/7c946ee5-04e7-498f-8236-597d2d5ff39d%40googlegroups.com.
