These clauses cause the loop to accumulate information about the
specified Lisp form. The accumulated result is returned
from the loop unless overridden, say, by a
collectappear elsewhere in this manual.
collecting is a synonym for
likewise for the other accumulation clauses.
maximizeis executed zero times.
Accumulation clauses can be followed by ‘into var’ to
cause the data to be collected into variable var (which is
let-bound during the loop) rather than an
unnamed temporary variable. Also,
into accumulations do
not automatically imply a return value. The loop must use some
explicit mechanism, such as
finally return, to return
the accumulated result.
It is valid for several accumulation clauses of the same type to accumulate into the same place. From Steele:
(cl-loop for name in '(fred sue alice joe june) for kids in '((bob ken) () () (kris sunshine) ()) collect name append kids) ⇒ (fred bob ken sue alice joe kris sunshine june)