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Update special conditionals documentation

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* doc/lispref/control.texi (Conditionals): Document if-let* and
when-let*, not if-let and when-let.  Document and-let*.
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Sean Whitton 2024-10-24 12:10:09 +08:00
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doc/lispref/control.texi
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@ -313,30 +313,41 @@ to make this easier and more readable. The above can be written the
following way instead: following way instead:
@example @example
(when-let ((result1 (do-computation)) (when-let* ((result1 (do-computation))
(result2 (do-more result1))) (result2 (do-more result1)))
(do-something result2)) (do-something result2))
@end example @end example
There's a number of variations on this theme, and they're briefly There's a number of variations on this theme, and they're briefly
described below. described below.
@defmac if-let spec then-form else-forms... @defmac if-let* varlist then-form else-forms...
Evaluate each binding in @var{spec} in turn, like in @code{let*} Evaluate each binding in @var{varlist} in turn, like in @code{let*}
(@pxref{Local Variables}), stopping if a binding value is @code{nil}. (@pxref{Local Variables}), stopping if a binding value is @code{nil}.
If all are non-@code{nil}, return the value of @var{then-form}, If all are non-@code{nil}, return the value of @var{then-form},
otherwise the last form in @var{else-forms}. otherwise the last form in @var{else-forms}.
@end defmac @end defmac
@defmac when-let spec then-forms... @defmac when-let* varlist then-forms...
Like @code{if-let}, but without @var{else-forms}. Like @code{if-let*}, but without @var{else-forms}.
@end defmac
@defmac and-let* varlist then-forms...
Like @code{when-let*}, but in addition, if there are no
@var{then-forms} and all the bindings evaluate to non-nil, return the
value of the last binding.
@end defmac @end defmac
@defmac while-let spec then-forms... @defmac while-let spec then-forms...
Like @code{when-let}, but repeat until a binding in @var{spec} is Like @code{when-let*}, but repeat until a binding in @var{spec} is
@code{nil}. The return value is always @code{nil}. @code{nil}. The return value is always @code{nil}.
@end defmac @end defmac
Some Lisp programmers follow the convention that @code{and} and
@code{and-let*} are for forms evaluated for return value, and
@code{when} and @code{when-let*} are for forms evaluated for side-effect
with returned values ignored.
@node Combining Conditions @node Combining Conditions
@section Constructs for Combining Conditions @section Constructs for Combining Conditions
@cindex combining conditions @cindex combining conditions