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POHow can I spot subtle Lisp syntax mistakes?
 

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  1. POHow can I spot subtle Lisp syntax mistakes?
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    <p>I'm a newbie playing around with Lisp (actually, Emacs Lisp). It's a lot of fun, except when I seem to run into the same syntax mistakes again and again.</p> <p>For instance, here's something I've encountered several times. I have some <code>cond</code> form, like</p> <pre><code>(cond ((foo bar) (qux quux)) ((or corge (grault warg)) (fred) (t xyzzy))) </code></pre> <p>and the default clause, which returns <code>xyzzy</code>, is never carried out, because it's actually nested inside the previous clause:</p> <pre><code>(cond ((foo bar) (qux quux)) ((or corge (grault warg)) (fred)) (t xyzzy)) </code></pre> <p>It's difficult for me to see such errors when the difference in indentation is only one space. Does this get easier with time?</p> <p>I also have problems when there's a large distance between the (mal-)indented line and the line it should be indented against. <code>let</code> forms with a lot of complex bindings, for example, or an <code>unless</code> form with a long conditional:</p> <pre><code>(defun test () (unless (foo bar (qux quux) (or corge (grault warg) (fred)))) xyzzy) </code></pre> <p>It turns out <code>xyzzy</code> was never inside the <code>unless</code> form at all:</p> <pre><code>(defun test () (unless (foo bar (qux quux) (or corge (grault warg) (fred))) xyzzy)) </code></pre> <p>I auto-indent habitually and use parenthesis highlighting to avoid counting parentheses. For the most part it works like a breeze, but occasionally, I discover my syntax mistakes only by debugging. What can I do?</p>
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    1. USTörök Gábor
    1. USMarius Andersen
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    1. COhttp://xkcd.com/224/
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      1. USDavid Schmitt
    2. COBetter: http://xkcd.com/297/
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      1. POHow can I spot subtle Lisp syntax mistakes?
      1. USErik Forbes
 

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