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eae798486a Update special conditionals documentation
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Sean Whitton 2024-10-24 12:13:20 +08:00
commit 698d75a335
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25
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:
@example
(when-let ((result1 (do-computation))
(result2 (do-more result1)))
(when-let* ((result1 (do-computation))
(result2 (do-more result1)))
(do-something result2))
@end example
There's a number of variations on this theme, and they're briefly
described below.
@defmac if-let spec then-form else-forms...
Evaluate each binding in @var{spec} in turn, like in @code{let*}
@defmac if-let* varlist then-form else-forms...
Evaluate each binding in @var{varlist} in turn, like in @code{let*}
(@pxref{Local Variables}), stopping if a binding value is @code{nil}.
If all are non-@code{nil}, return the value of @var{then-form},
otherwise the last form in @var{else-forms}.
@end defmac
@defmac when-let spec then-forms...
Like @code{if-let}, but without @var{else-forms}.
@defmac when-let* varlist then-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
@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}.
@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
@section Constructs for Combining Conditions
@cindex combining conditions