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Mishaps are an everyday part of programming. Sometimes they are the result of giving a POP-11 procedure the wrong type of input; sometimes, as in the example below, they are caused by a character left out, a word mistyped, or a symbol put in the wrong place.

length [the cat] ) =>

;;; INVOLVING: length [
;;; DOING : compile

Occasionally a mishap message can be hard to understand, but generally they are informative. The first line of the message gives the type of mishap: in this case a missing separator, the ( character. The next line gives the position of the mishap (between length and [), and the third line is a `calling sequence' that would give an experienced programmer more information about where the mishap occurred.

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