

                                                                   next-in

    MACRO
NEXT-IN GENERATOR {ACTION}*                                         [Macro]

    Package
    series

    DESCRIPTION

NEXT-IN returns the next element in the generator GENERATOR.  The ACTIONS
can be any Lisp expressions.  They are evaluated if and only if no more
elements can be retrieved from GENERATOR.  If there are no more elements
and no actions, it is an error.  It is also an error to apply NEXT-IN to a
generator a second time after the generator has run out of elements.  As an
example of generators, consider the following.

(LET ((X (GENERATOR (SCAN '(1 2 3 4))))) 
  (WITH-OUTPUT-TO-STRING (S) 
    (LOOP (PRIN1 (NEXT-IN X (RETURN)) S) 
          (PRIN1 (NEXT-IN X (RETURN)) S) 
          (PRINC "," S)))) 
 => "12,34,"

     SEE ALSO
     about-series
     about-generators

;Copyright 1989 by the Massachusetts Institute of Technology,
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