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| author | Noam Postavsky <npostavs@gmail.com> | 2018-03-31 00:40:43 -0400 |
|---|---|---|
| committer | Noam Postavsky <npostavs@gmail.com> | 2018-03-31 00:50:37 -0400 |
| commit | e50196e8a96216f1fd69f9257cddd8d76ad2ac78 (patch) | |
| tree | 0cc120b6a633ce87db822016922c1df4976f2f65 | |
| parent | 8a2466ff7240136c32b1cc21143225935d462cc6 (diff) | |
| download | emacs-e50196e8a96216f1fd69f9257cddd8d76ad2ac78.tar.gz | |
Document return value of pcase (Bug#30425)
* doc/lispref/control.texi (Pattern matching case statement):
* lisp/emacs-lisp/pcase.el (pcase): State that pcase returns nil if no
patterns match.
(pcase-exhaustive): State that an error is signaled if no patterns
match.
| -rw-r--r-- | doc/lispref/control.texi | 3 | ||||
| -rw-r--r-- | lisp/emacs-lisp/pcase.el | 7 |
2 files changed, 7 insertions, 3 deletions
diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi index f85ee947790..adec632da6a 100644 --- a/doc/lispref/control.texi +++ b/doc/lispref/control.texi @@ -317,7 +317,8 @@ list of the form @code{(@var{pattern} @var{body-forms}@dots{})}. @var{pattern} of each clause, in textual order. If the value matches, the clause succeeds; @code{pcase} then evaluates its @var{body-forms}, and returns the value of the last of @var{body-forms}. Any remaining -@var{clauses} are ignored. +@var{clauses} are ignored. If no clauses match, then the @code{pcase} +form evaluates to @code{nil}. The @var{pattern} part of a clause can be of one of two types: @dfn{QPattern}, a pattern quoted with a backquote; or a diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el index 6cfd074cf0b..ce148c9e1a9 100644 --- a/lisp/emacs-lisp/pcase.el +++ b/lisp/emacs-lisp/pcase.el @@ -118,7 +118,9 @@ two element list, binding its elements to symbols named `foo' and A significant difference from `cl-destructuring-bind' is that, if a pattern match fails, the next case is tried until either a -successful match is found or there are no more cases. +successful match is found or there are no more cases. The CODE +expression corresponding to the matching pattern determines the +return value. If there is no match the returned value is nil. Another difference is that pattern elements may be quoted, meaning they must match exactly: The pattern \\='(foo bar) @@ -211,7 +213,8 @@ Emacs Lisp manual for more information and examples." ;;;###autoload (defmacro pcase-exhaustive (exp &rest cases) - "The exhaustive version of `pcase' (which see)." + "The exhaustive version of `pcase' (which see). +If EXP fails to match any of the patterns in CASES, an error is signaled." (declare (indent 1) (debug pcase)) (let* ((x (gensym "x")) (pcase--dontwarn-upats (cons x pcase--dontwarn-upats))) |