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(cl)Assignment

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Assignment
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The `psetq' form is just like `setq', except that multiple assignments
are done in parallel rather than sequentially.

 - Special Form: psetq [symbol form]...
     This special form (actually a macro) is used to assign to several
     variables simultaneously.  Given only one SYMBOL and FORM, it has
     the same effect as `setq'.  Given several SYMBOL and FORM pairs,
     it evaluates all the FORMs in advance and then stores the
     corresponding variables afterwards.

          (setq x 2 y 3)
          (setq x (+ x y)  y (* x y))
          x
               => 5
          y                     ; `y' was computed after `x' was set.
               => 15
          (setq x 2 y 3)
          (psetq x (+ x y)  y (* x y))
          x
               => 5
          y                     ; `y' was computed before `x' was set.
               => 6

     The simplest use of `psetq' is `(psetq x y y x)', which exchanges
     the values of two variables.  (The `rotatef' form provides an even
     more convenient way to swap two variables; Note: Modify Macros.)

     `psetq' always returns `nil'.