As a user of bleeding-edge emacs builds (where lexical-binding: t in slime.el actually matters), I'd like to warn SLIME developers than LEXICAL-LET and LEXICAL-LET* macros are now broken in this mode. They expand into code that mixes (symbol-value) with let-bindings on a dynamically-generated name, assuming that it will be accessed as special, not lexical, variable.

If lexical-binding is actually available in emacs, bare LET and LET* should be used instead (tried and worked).

I worked around it within my local emacsen by redefinieng lexical-let[*], so they examine `lexical-binding' at expansion time, and expand into LET[*] if appropriate.

The same thing could be done in slime.el (and something should be done, IMHO -- in the worst case, removing lexical-binding: t until the issue is fixed in Emacs). The following macros may provide a compatible replacement for both new and old emacs versions:

;; If you know a cleaner way to test whether emacs supports ;; lexical binding, feel free to rewrite the macro below: (defmacro lexical-bind-dispatch (lexical nolexical &rest body) "Dispatch to `lexical' or `nolexical' depending on `lexical-binding': Expand into (lexical...) if lexical-binding is set and supported by emacs, and into (nolexical...) otherwise" (if (and lexical-binding (let (should-not-become-boundp) (not (boundp 'should-not-become-boundp)))) `(,lexical ,@body) `(,nolexical ,@body)))

(defmacro lex-let* (bindings &rest body) `(lexical-bind-dispatch let* lexical-let* ,bindings ,@body))

(defmacro lex-let (bindings &rest body) `(lexical-bind-dispatch let lexical-let ,bindings ,@body))