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ANSI Common Lisp  10 Symbols 10.2 Dictionary of Symbols
- Syntax:
-
gensym
&optional x
 new-symbol
- Arguments and Values:
-
x - a string or a non-negative integer.
Complicated defaulting behavior; see below.
new-symbol - a fresh, uninterned symbol.
- Description:
-
Creates and returns a fresh, uninterned symbol,
as if by calling make-symbol. (The only difference between
gensym and make-symbol is in how the new-symbol's
name is determined.)
The name of the new-symbol is the concatenation
of a prefix, which defaults to "G", and
a suffix, which is the decimal representation of a number that
defaults to the value of *gensym-counter*.
If x is supplied, and is a string, then that string
is used as a prefix instead of "G" for this call to gensym only.
If x is supplied, and is an integer, then that integer,
instead of the value of *gensym-counter*, is used as the suffix
for this call to gensym only.
If and only if no explicit suffix is supplied,
*gensym-counter* is incremented after it is used.
- Examples:
-
(setq sym1 (gensym)) #:G3142
(symbol-package sym1) NIL
(setq sym2 (gensym 100)) #:G100
(setq sym3 (gensym 100)) #:G100
(eq sym2 sym3) false
(find-symbol "G100") NIL, NIL
(gensym "T") #:T3143
(gensym) #:G3144
- Side Effects:
-
Might increment *gensym-counter*.
- Affected By:
-
*gensym-counter*
- Exceptional Situations:
-
Should signal an error of type type-error if x is not a string or a non-negative integer.
- See Also:
-
gentemp,
*gensym-counter*
- Notes:
-
The ability to pass a numeric argument to gensym has been deprecated;
explicitly binding *gensym-counter* is now stylistically preferred.
(The somewhat baroque conventions for the optional argument are historical
in nature, and supported primarily for compatibility with older dialects
of Lisp. In modern code, it is recommended that the only kind of argument
used be a string prefix. In general, though, to obtain more flexible control
of the new-symbol's name, consider using make-symbol instead.)
- Allegro CL Implementation Details:
-
None.
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