On Mon, 5 Mar 2007, Robert St. Amant wrote:

New subscriber here--I hope this isn't something that's already been discussed, and that it's targeted at the right mailing list.

During a class I'm teaching, I typed the following into the REPL:

CL-USER> (macroexpand '(prog1 1)) (LET ((#:G74 1)) #:G74) T

To show my students how the reader handles gensyms, I then cut and pasted the result above:

CL-USER> (LET ((#:G74 1)) #:G74) 1

This was unexpected. I then tried typing the same form in, which gave what I expected, an error:

CL-USER> (let ((#:g74 1)) #:g74) ;Compiler warnings : ; Undeclared free variable #:G74, in an anonymous lambda form. ; Unused lexical variable #:G74, in an anonymous lambda form. Invoking restart: Abort handling SLIME request. ; Evaluation aborted

Am I suffering under a basic misunderstanding about what should happen in this situation? It looks as if in the second expression above, the reader is somehow being bypassed for input that comes out the kill ring.

No, you're suffering from presentations :-)

Set (or customize) slime-repl-enable-presentations to nil to avoid such mishaps.

Andras