-;;; 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:
;;;###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
(pcase--dontwarn-upats (cons x pcase--dontwarn-upats)))
(pcase--expand
;; FIXME: Could we add the FILE:LINE data in the error message?
- exp (append cases `((,x (error "No clause matching ‘%S’" ,x)))))))
+ exp (append cases `((,x (error "No clause matching `%S'" ,x)))))))
;;;###autoload
(defmacro pcase-lambda (lambda-list &rest body)
(numberp . stringp)
(numberp . byte-code-function-p)
(consp . arrayp)
+ (consp . atom)
(consp . vectorp)
(consp . stringp)
(consp . byte-code-function-p)
(let ((code (pcase--u1 matches code vars rest)))
(if (eq upat '_) code
(macroexp--warn-and-return
- "Pattern t is deprecated. Use ‘_’ instead"
+ "Pattern t is deprecated. Use `_' instead"
code))))
((eq upat 'pcase--dontcare) :pcase--dontcare)
((memq (car-safe upat) '(guard pred))
(pcase--u rest))
vars
(list `((and . ,matches) ,code . ,vars))))
- (t (error "Unknown pattern ‘%S’" upat)))))
+ (t (error "Unknown pattern `%S'" upat)))))
(t (error "Incorrect MATCH %S" (car matches)))))
(def-edebug-spec
pcase-QPAT
+ ;; Cf. edebug spec for `backquote-form' in edebug.el.
(&or ("," pcase-PAT)
- (pcase-QPAT . pcase-QPAT)
+ (pcase-QPAT [&rest [¬ ","] pcase-QPAT]
+ . [&or nil pcase-QPAT])
(vector &rest pcase-QPAT)
sexp))