X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/6afef3f6ca2f3009c722b84e249903b7f807b044..3dd82d7501a28c1ac6cebb9a2fc14399413b5c40:/lisp/emacs-lisp/pcase.el

diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
index ea4f38add7..7e164c0fe5 100644
--- a/lisp/emacs-lisp/pcase.el
+++ b/lisp/emacs-lisp/pcase.el
@@ -1,6 +1,6 @@
-;;; pcase.el --- ML-style pattern-matching macro for Elisp -*- lexical-binding: t; coding: utf-8 -*-
+;;; pcase.el --- ML-style pattern-matching macro for Elisp -*- lexical-binding: t -*-
 
-;; Copyright (C) 2010-2015 Free Software Foundation, Inc.
+;; Copyright (C) 2010-2016 Free Software Foundation, Inc.
 
 ;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
 ;; Keywords:
@@ -107,38 +107,57 @@
 
 ;;;###autoload
 (defmacro pcase (exp &rest cases)
-  "Perform ML-style pattern matching on EXP.
+  "Evaluate EXP and attempt to match it against structural patterns.
 CASES is a list of elements of the form (PATTERN CODE...).
 
-Patterns can take the following forms:
+A structural PATTERN describes a template that identifies a class
+of values.  For example, the pattern \\=`(,foo ,bar) matches any
+two element list, binding its elements to symbols named `foo' and
+`bar' -- in much the same way that `cl-destructuring-bind' would.
+
+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.
+
+Another difference is that pattern elements may be quoted,
+meaning they must match exactly: The pattern \\='(foo bar)
+matches only against two element lists containing the symbols
+`foo' and `bar' in that order.  (As a short-hand, atoms always
+match themselves, such as numbers or strings, and need not be
+quoted.)
+
+Lastly, a pattern can be logical, such as (pred numberp), that
+matches any number-like element; or the symbol `_', that matches
+anything.  Also, when patterns are backquoted, a comma may be
+used to introduce logical patterns inside backquoted patterns.
+
+The complete list of standard patterns is as follows:
+
   _		matches anything.
   SYMBOL	matches anything and binds it to SYMBOL.
+                If a SYMBOL is used twice in the same pattern
+                the second occurrence becomes an `eq'uality test.
   (or PAT...)	matches if any of the patterns matches.
   (and PAT...)	matches if all the patterns match.
-  \\='VAL		matches if the object is `equal' to VAL
+  \\='VAL		matches if the object is `equal' to VAL.
   ATOM		is a shorthand for \\='ATOM.
 		   ATOM can be a keyword, an integer, or a string.
   (pred FUN)	matches if FUN applied to the object returns non-nil.
   (guard BOOLEXP)	matches if BOOLEXP evaluates to non-nil.
   (let PAT EXP)	matches if EXP matches PAT.
   (app FUN PAT)	matches if FUN applied to the object matches PAT.
-If a SYMBOL is used twice in the same pattern (i.e. the pattern is
-\"non-linear\"), then the second occurrence is turned into an `eq'uality test.
 
-FUN can take the form
+Additional patterns can be defined using `pcase-defmacro'.
+
+The FUN argument in the `app' pattern may have the following forms:
   SYMBOL or (lambda ARGS BODY)  in which case it's called with one argument.
   (F ARG1 .. ARGn) in which case F gets called with an n+1'th argument
                         which is the value being matched.
-So a FUN of the form SYMBOL is equivalent to one of the form (FUN).
+So a FUN of the form SYMBOL is equivalent to (FUN).
 FUN can refer to variables bound earlier in the pattern.
-FUN is assumed to be pure, i.e. it can be dropped if its result is not used,
-and two identical calls can be merged into one.
-E.g. you can match pairs where the cdr is larger than the car with a pattern
-like \\=`(,a . ,(pred (< a))) or, with more checks:
-\\=`(,(and a (pred numberp)) . ,(and (pred numberp) (pred (< a))))
-
-Additional patterns can be defined via `pcase-defmacro'.
-Currently, the following patterns are provided this way:"
+
+See Info node `(elisp) Pattern matching case statement' in the
+Emacs Lisp manual for more information and examples."
   (declare (indent 1) (debug (form &rest (pcase-PAT body))))
   ;; We want to use a weak hash table as a cache, but the key will unavoidably
   ;; be based on `exp' and `cases', yet `cases' is a fresh new list each time
@@ -865,8 +884,10 @@ Otherwise, it defers to REST which is a list of branches of the form
 
 (def-edebug-spec
   pcase-QPAT
+  ;; Cf. edebug spec for `backquote-form' in edebug.el.
   (&or ("," pcase-PAT)
-       (pcase-QPAT . pcase-QPAT)
+       (pcase-QPAT [&rest [&not ","] pcase-QPAT]
+		   . [&or nil pcase-QPAT])
        (vector &rest pcase-QPAT)
        sexp))