LispForum

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(loop for a in L
          when (consp (condition-on a))
          do (return (condition-on a)))

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(loop for a in L
         for condition = (condition-on a)
          when (consp condition)
          do (return condition))

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    (loop for f in g
          when (>= f  tr)
          for fc = (foo f)
          when (consp fc)
          collecting fc))

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(loop for f in g
          as fc = (and (>= f tr) (foo f))
          when (consp fc)
          collect fc)

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(let ((results nil))
  (dolist (f g (nreverse results))
    (when (>= f tr)
      (let ((fc (foo f)))
        (when (consp fc) (push fc results)))))

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(defun process (f)
  (when (> f tr) 
    (let ((fc (foo f)))
       (and (consp fc) (list fc)))))

(mapcan #'process g)

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(defun foo (f) (if (evenp f) (list f) f))
(loop for f in '(1 2 3 4)
      as fc = (and (>= f 2) (foo f))
      when (consp fc)
      collect fc)

;; gives ==>  ((2) (4))