4.1.6 Assignments

syntax: set! <variable> <expression>

<Expression> is evaluated, and the resulting value is stored in the location to which <variable> is bound. <Variable> must be bound either in some region enclosing the ‘set!’ expression or at top level. The result of the ‘set!’ expression is unspecified.

(define x 2) (+ x 1) ==> 3 (set! x 4) ==> unspecified (+ x 1) ==> 5