gensym returning same symbol

[Bob Felts]

gensym.lisp:
   (defmacro foo ()
     (format t "gensym=~s~%" (gensym)))

   (foo)
   (foo)
   (foo)

; compiling file "/Users/wrf3/gensym.lisp" (written 07 APR 2018 05:54:21 PM):
gensym=#:G0
gensym=#:G0
gensym=#:G0

sbcl --version
SBCL 1.4.6.51-b9e029d96

But LispWorks returns unique symbols:

;;; Safety = 3, Speed = 1, Space = 1, Float = 1, Interruptible = 1
;;; Compilation speed = 1, Debug = 2, Fixnum safety = 3
;;; Source level debugging is on
;;; Source file recording is on
;;; Cross referencing is on
; (TOP-LEVEL-FORM 0)
; FOO
gensym=#:G1567
; (TOP-LEVEL-FORM 2)
gensym=#:G1568
; (TOP-LEVEL-FORM 3)
gensym=#:G1569
; (TOP-LEVEL-FORM 4)

uname -a
Darwin wrf3s-MacBook-Pro.local 17.5.0 Darwin Kernel Version 17.5.0: Mon Mar 5 22:24:32 PST 2018; root:xnu-4570.51.1~1/RELEASE_X86_64 x86_64

*features*
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 :ASDF2 :ASDF :OS-MACOSX :OS-UNIX :NON-BASE-CHARS-EXIST-P :ASDF-UNICODE :64-BIT
 :64-BIT-REGISTERS :ALIEN-CALLBACKS :ANSI-CL :ASH-RIGHT-VOPS :BSD
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 :UNBIND-N-VOP :UNDEFINED-FUN-RESTARTS :UNIX :UNWIND-TO-FRAME-AND-CALL-VOP
 :X86-64)

[Stas Boukarev (stassats)]

Those are actually different symbols but with the same name.

[Bob Felts (wrf3)]

In theory, that makes sense. Someone with my name isn't me. But because of the contortions I'm going through to generate code at compile time, I had expected gensym to return different names on each invocation, like it does outside of macros. But I've worked around it by maintaining my own counter so that I can get the uniqueness I need.