For example, suppose that
in implementation A, the features spice and perq are present,
but the feature lispm is not present;
in implementation B, the feature lispm is present,
but the features spice and perq are
not present;
and
in implementation C, none of the features spice, lispm, or perq are
present.
Figure 24–1 shows some sample expressions, and how they would be
read_2 in these implementations.
(cons #+spice "Spice" #-spice "Lispm" x)
in implementation A ... (CONS "Spice" X)
in implementation B ... (CONS "Lispm" X)
in implementation C ... (CONS "Lispm" X)
(cons #+spice "Spice" #+LispM "Lispm" x)
in implementation A ... (CONS "Spice" X)
in implementation B ... (CONS "Lispm" X)
in implementation C ... (CONS X)
(setq a '(1 2 #+perq 43 #+(not perq) 27))
in implementation A ... (SETQ A '(1 2 43))
in implementation B ... (SETQ A '(1 2 27))
in implementation C ... (SETQ A '(1 2 27))
(let ((a 3) #+(or spice lispm) (b 3)) (foo a))
in implementation A ... (LET ((A 3) (B 3)) (FOO A))
in implementation B ... (LET ((A 3) (B 3)) (FOO A))
in implementation C ... (LET ((A 3)) (FOO A))
(cons #+Lispm "#+Spice" #+Spice "foo" #-(or Lispm Spice) 7 x)
in implementation A ... (CONS "foo" X)
in implementation B ... (CONS "#+Spice" X)
in implementation C ... (CONS 7 X)