macro hygiene escaping breaks let f(x)=...

[stevengj]

julia> macro foo()
       f = esc(:f); :(let $f(x) = x; $f(3); end)
       end
@foo (macro with 1 method)

julia> @foo
ERROR: syntax: invalid function name "(escape f)"

julia> macroexpand(:(@foo))
:($(Expr(:error, "invalid function name \"(escape f)\"")))

It looks like macroexpand.scm is forgetting to unescape somewhere. @JeffBezanson, any ideas?

(I'm running into this when trying to fix a bug I found in #20164.)

[stevengj]

It might be helpful if I could print a Scheme stack trace to see the Scheme stack at the point of the error, but (print-stack-trace (stacktrace)) doesn't seem to be working... is it being intercepted somehow when flisp is running inside the Julia parser?

[stevengj]

It looks like the error is occurring in the vars-introduced-by-patterns function. In particular, I think the problem may be that vars-introduced-by-patterns is calling julia-expand0 for let statements with functions, and julia-expand0 (normally called after macro expansion) doesn't recognize escapes.

[vtjnash]

I think the solution here is to teach expand-forms about escape, so that we can accurately use the resolve-scopes pass (and remove this preprocessing step), instead of attempting to just handle most common patterns in the macroexpand and hoping resolve-scopes gets the same answer. As it is, it already can miss other syntax forms, or get confused by them.