Syntax:

rebinding (var*) form* => result-form

Arguments and Values:

vars---the variables to be rebound.

form---an implicit progn.

result-form---a Lisp form.

Description:

Rebinding returns a Lisp form which creates a temporary binding for each variable var. Each var will be evaluated exactly once within result-form, in the order in which the variables are named in vars.

References within the forms to any variable named in vars will appear in result-form as a reference to the temporary binding for the variable.

Example:

 (defmacro lister (x y)
    (rebinding (x y)
       `(list ,x ,y)))
 => LISTER
 (macroexpand '(lister i j))
 => (LET ((#1=#:X I)
          (#2=#:Y J))
      (LIST #1# #2#))
 ;; The actual uninterned symbol names may vary with different
 ;; implementations.  For example, symbols produced by gensym
 ;; might be used.

May increment *GENSYM-COUNTER*.

Affected By:

Symbol names be be effected by *GENSYM-COUNTER*.

Exceptional Situations: None.

See Also:

with-unique-names, gensym.

Notes:

Rebinding is intended to facilitate the creation of hygienic macros, in which:

• The argument forms to the macro are evaluated in the expanded code once and once only, in the specified order.
• The names used as formal parameters in the macro definition do not appear in the generated code, so there is no danger of unwanted variable capture.

Rebinding is compatible with similarly named facilities in other Lisp implementations. It is related to the once-only facility defined in some Lisp implementations.