dolist

Type:	-	special form (fsubr)
Source:	-	xlcont.c

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
returns - the return value of the result expression or NIL

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 'exprs', 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"

See the dolist special form in the XLISP 2.0 manual.

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