pair::=var form

*form*- a*form*.

Assigns values to *variables*.

This is just like **setq**, except that the assignments happen "in parallel." That is, first all of the forms are evaluated, and only then are the variables set to the resulting values. In this way, the assignment to one variable does not affect the value computation of another in the way that would occur with **setq**'s sequential assignment.

If any *var* refers to a *binding* made by **symbol-macrolet**, then that *var* is treated as if **psetf** (not **psetq**) had been used.

A simple use of **psetq** to establish values for variables. As a matter of style, many programmers would prefer **setq** in a simple situation like this where parallel assignment is not needed, but the two have equivalent effect.

;;; TODO condemn toplevel PSETQ

(psetq a 1 b 2 c 3)

→NIL

a

→1

b

→2

c

→3

Use of **psetq** to update values by parallel assignment. The effect here is very different than if **setq** had been used.

(psetq a (1+ b) b (1+ a) c (+ a b))

→NIL

a

→3

b

→2

c

→3

Use of **psetq** on a symbol macro.

(let ((x (list 10 20 30))) (symbol-macrolet ((y (car x)) (z (cadr x))) (psetq y (1+ z) z (1+ y)) (list x y z)))

→((21 11 30) 21 11)

Use of parallel assignment to swap values of A and B.

(let ((a 1) (b 2)) (psetq a b b a) (values a b))

→2 1

The values of *forms* are assigned to *vars*.

None.

None.

None.

\issue{SYMBOL-MACROLET-SEMANTICS:SPECIAL-FORM}