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dolist

dolist

type: special form (fsubr)
location: built-in
source file: xlcont.c
Common LISP compatible: yes
supported on: all machines

SYNTAX

(dolist  ( <symbol> <list-expr> [ <result> ] ) [ <expr> ... ]  )
        <symbol>        -       a symbol
        <list-expr>     -       a list expression 
        <result>        -       an optional expression for the returned result
        <expr>          -       expressions comprising the body of the loop
                                which may contain RETURNs, GOs or tags for GO  

DESCRIPTION

The DOLIST special form is basically a list-oriented 'for' looping construct that contains a loop <symbol>, a <list-expr> to draw values from, an optional return value and a block of code (expressions) to evaluate. The sequence of execution is:

<symbol>  := CAR of <list-expr>
temp-list := CDR of <list-expr>
while  temp-list is not empty
        loop code execution
        <symbol>  := CAR of temp-list
        temp-list := CDR of temp-list
end-while
return <result>

The main loop <symbol> will take on successive values from <list-expr>. The DOLIST form will go through and create and initialize the <symbol>. After execution of the loop <expr>'s, the <symbol> is set to the next value in the <list-expr>. This continues until the <list-expr> has been exhausted. The value of the <result> expression is evaluated and returned. If no <result> is specified, NIL is returned. When the DOLIST is finished execution, the <symbol> that was defined will no longer exist or retain its value. If the <list-expr> is an empty list, then no loop execution takes place and the <result> is returned.

EXAMPLES

(dolist (i () "done")                   ; DOLIST with I loop variable
        (print "here"))                 ;   an empty list 
                                        ;   and a return value
                                        ;   returns "done"      
(dolist (x '(a b c) "fini")             ; DOLIST with X loop variable
        (princ x))                      ;   a list with (A B C)
                                        ;   and a return value
                                        ;   prints  ABC   returns "fini"
(dolist (y '(1 2 3))                    ; DOLIST with Y loop variable
        (princ (* y y)))                ;   a list with (1 2 3)
                                        ;   and no return value
                                        ;   prints  149   returns NIL
                                        ;   returns "met in the middle"


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