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comparison man/lispref/control.texi @ 2297:13a418960a88

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[xemacs-hg @ 2004-09-22 02:05:42 by stephent] various doc patches <87isa7awrh.fsf@tleepslib.sk.tsukuba.ac.jp>
author stephent
date Wed, 22 Sep 2004 02:06:52 +0000
parents 37e56e920ac5
children 755ae5b97edb
comparison
equal deleted inserted replaced
2296:a58ea4d0d0cd 2297:13a418960a88
618 We still have two return points, but this time only the outer one has 618 We still have two return points, but this time only the outer one has
619 the tag @code{hack}; the inner one has the tag @code{quux} instead. 619 the tag @code{hack}; the inner one has the tag @code{quux} instead.
620 Therefore, @code{throw} makes the outer @code{catch} return the value 620 Therefore, @code{throw} makes the outer @code{catch} return the value
621 @code{yes}. The function @code{print} is never called, and the 621 @code{yes}. The function @code{print} is never called, and the
622 body-form @code{'no} is never evaluated. 622 body-form @code{'no} is never evaluated.
623
624 In most cases the formal tag for a catch is a quoted symbol or a
625 variable whose value is a symbol. Both styles are demonstrated above.
626 In definitions of derived control structures, an anonymous tag may be
627 desired. A gensym could be used, but since catch tags are compared
628 using @code{eq}, any Lisp object can be used. An occasionally
629 encountered idiom is to bind a local variable to @code{(cons nil nil)},
630 and use the variable as the formal tag.
623 631
624 @node Errors 632 @node Errors
625 @subsection Errors 633 @subsection Errors
626 @cindex errors 634 @cindex errors
627 635