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Fix missing arg in pcase example.

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* doc/lispref/control.texi (Pattern matching case statement): Fix missing
argument in simple expression language sample.  Add
some sample programs written in that language.  Mention that
`pcase' requires lexical binding.

Fixes: debbugs:16238
This commit is contained in:
Tassilo Horn 2013-12-24 16:30:59 +01:00
parent 1139b0be8b
commit a956004715
2 changed files with 21 additions and 1 deletions
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7
doc/lispref/ChangeLog
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@ -1,3 +1,10 @@
2013-12-24 Tassilo Horn <tsdh@gnu.org>
* control.texi (Pattern matching case statement): Fix missing
argument in simple expression language sample (Bug#16238). Add
some sample programs written in that language. Mention that
`pcase' requires lexical binding.
2013-12-23 Xue Fuqiao <xfq.free@gmail.com>
* eval.texi (Special Forms): Document `special-form-p'.

15
doc/lispref/control.texi
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@ -328,7 +328,7 @@ expression language could look like:
(defun evaluate (exp env)
(pcase exp
(`(add ,x ,y) (+ (evaluate x env) (evaluate y env)))
(`(call ,fun ,arg) (funcall (evaluate fun) (evaluate arg env)))
(`(call ,fun ,arg) (funcall (evaluate fun env) (evaluate arg env)))
(`(fn ,arg ,body) (lambda (val)
(evaluate body (cons (cons arg val) env))))
((pred numberp) exp)
@ -342,6 +342,19 @@ third elements and binds them to the variables @code{x} and @code{y}.
@code{(pred numberp)} is a pattern that simply checks that @code{exp}
is a number, and @code{_} is the catch-all pattern that matches anything.
Here are some sample programs including their evaluation results:
@example
(evaluate '(add 1 2) nil) ;=> 3
(evaluate '(add x y) '((x . 1) (y . 2))) ;=> 3
(evaluate '(call (fn x (add 1 x)) 2) nil) ;=> 3
(evaluate '(sub 1 2) nil) ;=> (error "Unknown expression (sub 1 2)")
@end example
Note that (parts of) @code{pcase} only work as expected with lexical
binding, so lisp files using @code{pcase} should have enable it
(@pxref{Using Lexical Binding}, for how to enable lexical binding).
There are two kinds of patterns involved in @code{pcase}, called
@emph{U-patterns} and @emph{Q-patterns}. The @var{upattern} mentioned above
are U-patterns and can take the following forms: