[Sbcl-devel] Bogus warning from loop?

[Nikodemus S. <tsi...@cc...>]

This was noted by Kalle Olavi Niemitalo on #lisp.

Current SBCL gives a warning on loops with multiple value-returning
termination clauses, which as far as I can tell are legal. The actual
macroexpansion looks just fine, though.

From CLHS:

 loop [name-clause] {variable-clause}* {main-clause}* => result*

 main-clause::= unconditional | accumulation | conditional |
                termination-test | initial-final

 termination-test::= while form | until form | repeat form | always form |
                     never form | thereis form

So loops like (loop thereis (foo) thereis (bar)) should be quite legal,
but SBCL isn't happy:

CL-USER(14): (macroexpand '(loop thereis :one thereis :two))
WARNING: The LOOP clause is providing a value for the iteration;
however, one was already established by a THEREIS clause.
current LOOP context: THEREIS :TWO.

(BLOCK NIL
  (LET ((#:LOOP-IT-2966 NIL))
    (SB-LOOP::LOOP-BODY NIL
                        NIL
                        ((WHEN (SETQ #:LOOP-IT-2966 :ONE)
                           (RETURN-FROM NIL #:LOOP-IT-2966))
                         (WHEN (SETQ #:LOOP-IT-2966 :TWO)
                           (RETURN-FROM NIL #:LOOP-IT-2966)))
                        NIL
                        NIL)))
T

Have I just hit my head somewhere, and are such forms actually bogus or
ill-defined?

Cheers,

 -- Nikodemus