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  • Re: nesting for loops

    From B. Pym@Nobody447095@here-nor-there.org to comp.lang.lisp,comp.lang.scheme on Fri Jul 18 23:40:15 2025
    From Newsgroup: comp.lang.lisp

    Barry Margolin wrote:

    b) Using a nested LOOP _may_ be indicative that you didn't use LOOP >properly, as you can put almost infinite complexity into a single
    LOOP.

    I suppose this is possible, but I don't think it's likely. Nested loops
    are extremely common whenever you're traversing multi-dimensional
    structures, e.g. a 2-d array with

    (loop for i upto length
    do
    (loop for j upto width
    do
    (do-something-with (aref a i j))))

    or a list of lists with:

    (loop for inner in outer
    do
    (loop for item in inner
    do
    (do-something-with item)))

    LOOP has quite a bit of complexity, but it doesn't actually have any way to do either of these easily in a single loop (well, in the first case you
    could do it with ROW-MAJOR-AREF, but that's not really a LOOP feature,
    that's a special array feature).

    Gauche Scheme:

    (use srfi-42) ;; list-ec

    (list-ec [:list i '(1 10 100)] [:list j '(7 8 9)] (* i j))

    (7 8 9 70 80 90 700 800 900)
    --
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