CLHS: Macro DOLIST

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Macro DOLIST

Syntax:

dolist (var list-form [result-form]) declaration* {tag | statement}*

=> result*

Arguments and Values:

var---a symbol.

list-form---a form.

result-form---a form.

declaration---a declare expression; not evaluated.

tag---a go tag; not evaluated.

statement---a compound form; evaluated as described below.

results---if a return or return-from form is executed, the values passed from that form; otherwise, the values returned by the result-form or nil if there is no result-form.

Description:

dolist iterates over the elements of a list. The body of dolist is like a tagbody. It consists of a series of tags and statements.

dolist evaluates list-form, which should produce a list. It then executes the body once for each element in the list, in the order in which the tags and statements occur, with var bound to the element. Then result-form is evaluated. tags label statements.

At the time result-form is processed, var is bound to nil.

An implicit block named nil surrounds dolist. return may be used to terminate the loop immediately without performing any further iterations, returning zero or more values.

The scope of the binding of var does not include the list-form, but the result-form is included.

It is implementation-dependent whether dolist establishes a new binding of var on each iteration or whether it establishes a binding for var once at the beginning and then assigns it on any subsequent iterations.

Examples:

     (setq temp-two '()) =>  NIL
     (dolist (temp-one '(1 2 3 4) temp-two) (push temp-one temp-two)) =>  (4 3 2 1)

     (setq temp-two 0) =>  0
     (dolist (temp-one '(1 2 3 4)) (incf temp-two)) =>  NIL
     temp-two =>  4

     (dolist (x '(a b c d)) (prin1 x) (princ " "))
    >>  A B C D
    =>  NIL

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

do, dotimes, tagbody, Section 3.6 (Traversal Rules and Side Effects)

Notes:

go may be used within the body of dolist to transfer control to a statement labeled by a tag.

The following X3J13 cleanup issues, not part of the specification, apply to this section:

- MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE
- DECLS-AND-DOC

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