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[elpa] externals/peg 585f4de 1/7: Create hg repo.

From: Stefan Monnier
Subject: [elpa] externals/peg 585f4de 1/7: Create hg repo.
Date: Sun, 10 Mar 2019 17:12:09 -0400 (EDT)

branch: externals/peg
commit 585f4de6643425b1b32d07dbba7b7b77bdc79b6e
Author: Helmut Eller <address@hidden>
Commit: Helmut Eller <address@hidden>

    Create hg repo.
 COPYING   | 674 ++++++++++++++++++++++++++++++++++++++++++++++++
 ChangeLog | 122 +++++++++
 README    |  29 +++
 peg.el    | 863 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1688 insertions(+)

diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..94a9ed0
--- /dev/null
@@ -0,0 +1,674 @@
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+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    GNU General Public License for more details.
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+Also add information on how to contact you by electronic and paper mail.
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
diff --git a/ChangeLog b/ChangeLog
new file mode 100644
index 0000000..577288c
--- /dev/null
+++ b/ChangeLog
@@ -0,0 +1,122 @@
+Author: Helmut Eller <address@hidden>
+Date:   Mon Dec 22 09:13:05 2008 +0100
+    Fix typo.
+Author: Helmut Eller <address@hidden>
+Date:   Sun Dec 21 09:38:06 2008 +0100
+    Version 0.5 for savannah.
+Author: Helmut Eller <address@hidden>
+Date:   Thu Dec 18 10:19:18 2008 +0100
+    Remove *list op.
+Author: Helmut Eller <address@hidden>
+Date:   Wed Dec 17 18:59:23 2008 +0100
+    Bump version number to 0.4.
+Author: Helmut Eller <address@hidden>
+Date:   Wed Dec 17 18:52:55 2008 +0100
+    Add some more operators for actions.
+    list: Factored out of *list.  Collects all items on the stack.
+    region: New. Pushes start and end.
+    replaces: Replaces match.
+Author: Helmut Eller <address@hidden>
+Date:   Wed Dec 17 18:08:28 2008 +0100
+    Fix normalizer for \`: Push values in left-to-right order.
+    peg-postprocess: turn positions in to markers to
+    support replacement ops in the actions.
+Author: Helmut Eller <address@hidden>
+Date:   Mon Dec 1 19:10:21 2008 +0100
+    (peg-ex-lisp): Minor change to allow comments in more places.
+Author: Helmut Eller <address@hidden>
+Date:   Mon Dec 1 15:19:31 2008 +0100
+    (peg-ex-uri): Fix some stack actions so that the file: example works.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 15:21:35 2008 +0100
+    Remove dups from char sets to avoid clashes with [:CLASS:] syntax.
+    There's still no way to include syntax classes in charsets. There
+    really should be.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 12:09:31 2008 +0100
+    Handle ^ in charsets.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 10:12:24 2008 +0100
+    Use (declare (indent )) again.  Emacs 21 compatibility is to hard
+    due to broken ,@ or something.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 08:50:10 2008 +0100
+    Don't use (declare (indent 3)) because that doesn' work in Emacs 21.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 08:44:03 2008 +0100
+    Fix minor spelling error.
+Author: Helmut Eller <address@hidden>
+Date:   Fri Nov 28 08:35:16 2008 +0100
+    Fix range translator: we need to check for eob.
+    Thanks to Hugo Schmitt.
+Author: Helmut Eller <address@hidden>
+Date:   Thu Nov 27 23:54:18 2008 +0100
+    *** empty log message ***
+Author: Helmut Eller <address@hidden>
+Date:   Thu Nov 27 23:52:25 2008 +0100
+    Make file byte-compileable in Emacs 22.
+Author: Helmut Eller <address@hidden>
+Date:   Thu Nov 27 10:07:40 2008 +0100
+    Add mini test suite
+    Restore subtring operator.
+    Add translate method for <fail>.
+Author: Helmut Eller <address@hidden>
+Date:   Thu Nov 27 09:26:33 2008 +0100
+    Add *list operator.
+Author: Helmut Eller <address@hidden>
+Date:   Sat Nov 8 14:37:40 2008 +0100
+    More friendly syntax for character sets.
+    For example (set A-Z 0-9 "_!-" ?%).
+    [A-Z] is now the same as (set A-Z) which should look familiar.
+    Fix bug in *-loops.  We must backtrack.
+    Add somewhat bigger examples to parse URIs and Lisp-style Sexps.
+Author: Helmut Eller <address@hidden>
+Date:   Thu Nov 6 12:18:26 2008 +0100
+    Detect infinite loops.
+    Use a single peg-add-method macro for all gfs.
+Author: Helmut Eller <address@hidden>
+Date:   Wed Nov 5 23:12:05 2008 +0100
+    Add peg.el.
diff --git a/README b/README
new file mode 100644
index 0000000..cc764e8
--- /dev/null
+++ b/README
@@ -0,0 +1,29 @@
+  This package implements Parsing Expression Grammars for Emacs Lisp.
+  PEGs are a formalism similar to the classical Context Free Grammars
+  but with some simplifications which makes the implementation of PEGs
+  as top-down parser particularly simple and easy to understand.  PEGs
+  are more expressive than regexps and potentially easier to use.
+  For more details and examples, see the header of peg.el.
+  The only required file is peg.el.  Just load it into Emacs.
+  GNU General Public License, version 3.  (Same license as Emacs.)
+  Send bug reports and suggested improvements to:
+    Helmut Eller <address@hidden>
+  [mailing list coming soon]
diff --git a/peg.el b/peg.el
new file mode 100644
index 0000000..8494d2f
--- /dev/null
+++ b/peg.el
@@ -0,0 +1,863 @@
+;;; peg.el --- Parsing Expression Grammars in Emacs Lisp
+;; Copyright 2008  Helmut Eller <address@hidden>.
+;; Version: 0.5 (2008-Dec-21)
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; GNU General Public License for more details.
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;; Commentary:
+;; Parsing Expression Grammars (PEG) are a formalism in the spirit of
+;; Context Free Grammars (CFG) with some simplifications which makes
+;; the implementation of PEGs as top-down parser particularly simple
+;; and easy to understand [Ford, Baker].
+;; This file implements a macro `peg-parse' which parses the current
+;; buffer according to a PEG.  E.g. we can match integers with a PEG
+;; like this:
+;;  (peg-parse (number   sign digit (* digit))
+;;             (sign     (or "+" "-" ""))
+;;             (digit    [0-9]))
+;; In contrast to regexps, PEGs allow us to define recursive rules.  A
+;; PEG is a list of rules.  A rule is written as (NAME PE ...).
+;; E.g. (sign (or "+" "-" "")) is a rule with the name "sign".  The
+;; syntax for Parsing Expression (PE) is a follows:
+;; Description         Lisp            Haskell, as in Ford's paper
+;; Sequence            (and e1 e2)     e1 e2
+;; Prioritized Choice   (or e1 e2)     e1 / e2
+;; Not-predicate       (not e)         !e
+;; And-predicate       (if e)          &e
+;; Any character       (any)           .
+;; Literal string      "abc"           "abc"
+;; Character C         (char c)        'c'
+;; Zero-or-more        (* e)           e*
+;; One-or-more                 (+ e)           e+
+;; Optional            (opt e)         e?
+;; Character range     (range a b)     [a-b]
+;; Character set       [a-b "+*" ?x]   [a-b+*x]  ; note: [] is a elisp vector
+;; Character classes    [ascii cntrl]
+;; Beginning-of-Buffer  (bob)
+;; End-of-Buffer        (eob)
+;; Beginning-of-Line    (bol)
+;; End-of-Line         (eol)
+;; Beginning-of-Word    (bow)
+;; End-of-Word         (eow)
+;; Beginning-of-Symbol  (bos)
+;; End-of-Symbol               (eos)
+;; Syntax-Class        (syntax-class NAME)
+;; `peg-parse' also supports parsing actions, i.e. Lisp snippets which
+;; are executed when a PE matches.  This can be used to construct
+;; syntax trees or for similar tasks.  Actions are written as
+;;  (action FORM)          ; evaluate FORM
+;;  `(VAR... -- FORM...)   ; stack action
+;; Actions don't consume input, but are executed at the point of
+;; match.  A "stack action" takes VARs from the "value stack" and
+;; pushes the result of evaluating FORMs to that stack.  See
+;; `peg-ex-parse-int' for an example.
+;; Derived Operators:
+;; The following operators are implemented as combinations of
+;; primitive expressions:
+;; (substring E)  ; match E and push the substring for the matched region
+;; (region E)     ; match E and push the corresponding start and end positions
+;; (replace E RPL); match E and replace the matched region with RPL.
+;; (list E)       ; match E and push a list of all items that E produces.
+;; Regexp equivalents:
+;; Here a some examples for regexps and how those could be written as PE.
+;; [Most are taken from rx.el]
+;; "^[a-z]*"
+;; (and (bol) (* [a-z]))
+;; "\n[^ \t]"
+;; (and "\n" (not [" \t"]) (any))
+;; "\\*\\*\\* EOOH \\*\\*\\*\n"
+;; "*** EOOH ***\n"
+;; "\\<\\(catch\\|finally\\)\\>[^_]"
+;; (and (bow) (or "catch" "finally") (eow) (not "_") (any))
+;; "[ \t\n]*:\\([^:]+\\|$\\)"
+;; (and (* [" \t\n"]) ":" (or (+ (not ":") (any)) (eol)))
+;; "^content-transfer-encoding:\\(\n?[\t ]\\)*quoted-printable\\(\n?[\t ]\\)*"
+;; (and (bol) 
+;;      "content-transfer-encoding:" 
+;;      (* (opt "\n") ["\t "])
+;;      "quoted-printable"
+;;      (* (opt "\n") ["\t "]))
+;; "\\$[I]d: [^ ]+ \\([^ ]+\\) "
+;; (and "$Id: " (+ (not " ") (any)) " " (+ (not " ") (any)) " ")
+;; "^;;\\s-*\n\\|^\n"
+;; (or (and (bol) ";;" (* (syntax-class whitespace)) "\n")
+;;     (and (bol) "\n"))
+;; "\\\\\\\\\\[\\w+"
+;; (and "\\\\[" (+ (syntax-class word)))
+;; Search forward for ";;; Examples" for other examples.
+;; References:
+;; [Ford] Bryan Ford. Parsing Expression Grammars: a Recognition-Based
+;; Syntactic Foundation. In POPL'04: Proceedings of the 31st ACM
+;; SIGPLAN-SIGACT symposium on Principles of Programming Languages,
+;; pages 111-122, New York, NY, USA, 2004. ACM Press.
+;; [Baker] Baker, Henry G. "Pragmatic Parsing in Common Lisp".  ACM Lisp
+;; Pointers 4(2), April--June 1991, pp. 3--15.
+(unless (>= emacs-major-version 22)
+  (error "peg.el requires Emacs version 22 or newer"))
+;;; Code:
+(defmacro peg-parse (&rest rules)
+  "Match RULES at point.
+Return (T STACK) if the match succeed and nil on failure."
+  (peg-translate-rules rules))
+(defmacro peg-parse-exp (exp)
+  "Match the parsing expression EXP at point.
+Note: a PE can't \"call\" rules by name."
+  `(let ((peg-thunks nil))
+     (when ,(peg-translate-exp (peg-normalize exp))
+       (peg-postprocess peg-thunks))))
+;; A table of the PEG rules.  Used during compilation to resolve
+;; references to named rules.
+(defvar peg-rules)
+;; used at runtime for backtracking.  It's a list ((POS . THUNK)...).
+;; Each THUNK is executed at the corresponding POS.  Thunks are
+;; executed in a postprocessing step, not during parsing.
+(defvar peg-thunks)
+;; The basic idea is to translate each rule to a lisp function.
+;; The result looks like
+;;   (let ((rule1 (lambda () code-for-rule1))
+;;         ...
+;;         (ruleN (lambda () code-for-ruleN)))
+;;     (funcall rule1))
+;; code-for-ruleX returns t if the rule matches and nil otherwise.
+(defun peg-translate-rules (rules)
+  "Translate the PEG RULES, to a top-down parser."
+  (let ((peg-rules (make-hash-table :size 20)))
+    (dolist (rule rules)
+      (puthash (car rule) 'defer peg-rules))
+    (dolist (rule rules)
+      (puthash (car rule) (peg-normalize `(and . ,(cdr rule))) peg-rules))
+    (peg-check-cycles peg-rules)
+    `(let ((peg-thunks '()) . ,(mapcar #'car rules))
+       ,@(mapcar (lambda (rule)
+                  (let ((name (car rule)))
+                    `(setq ,name
+                           (lambda ()
+                             ,(peg-translate-exp (gethash name peg-rules))))))
+                rules)
+       (when (funcall ,(car (car rules)))
+        (peg-postprocess peg-thunks)))))
+  (defun peg-method-table-name (method-name)
+    (intern (format "peg-%s-methods" method-name))))
+(defmacro peg-define-method-table (name)
+  (let ((tab (peg-method-table-name name)))
+    `(progn
+       (defvar ,tab)
+       (setq ,tab (make-hash-table :size 20)))))
+(defmacro peg-add-method (method type args &rest body)
+  (declare (indent 3))
+  `(puthash ',type (lambda ,args . ,body) ,(peg-method-table-name method)))
+(peg-define-method-table normalize)
+;; Internally we use a regularized syntax, e.g. we only have binary OR
+;; nodes.  Regularized nodes are lists of the form (OP ARGS...).
+(defun peg-normalize (exp)
+  "Return a \"normalized\" form of EXP."
+  (cond ((and (consp exp)
+             (let ((fun (gethash (car exp) peg-normalize-methods)))
+               (and fun 
+                    (apply fun (cdr exp))))))
+       ((stringp exp)
+        (let ((len (length exp)))
+          (cond ((zerop len) '(null))
+                ((= len 1) `(char ,(aref exp 0)))
+                (t `(str ,exp)))))
+       ((and (symbolp exp) exp)
+        (when (not (gethash exp peg-rules))
+          (error "Reference to undefined PEG rule: %S" exp))
+        `(call ,exp))
+       ((vectorp exp)
+        (peg-normalize `(set . ,(append exp '()))))
+       (t
+        (error "Invalid parsing expression: %S" exp))))
+(defvar peg-leaf-types '(null fail any call action char range str set
+                             bob eob bol eol bow eow bos eos syntax-class))
+(dolist (type peg-leaf-types)
+  (puthash type `(lambda (&rest args) (cons ',type args)) 
+          peg-normalize-methods))
+(peg-add-method normalize or (&rest args)
+  (cond ((null args) '(fail))
+       ((null (cdr args)) (peg-normalize (car args)))
+       (t `(or ,(peg-normalize (car args)) 
+               ,(peg-normalize `(or . ,(cdr args)))))))
+(peg-add-method normalize and (&rest args)
+  (cond ((null args) '(null))
+       ((null (cdr args)) (peg-normalize (car args)))
+       (t `(and ,(peg-normalize (car args)) 
+                ,(peg-normalize `(and . ,(cdr args)))))))
+(peg-add-method normalize * (&rest args)
+  `(* ,(peg-normalize `(and . ,args))))
+;; FIXME: this duplicates code; could use some loop to avoid that
+(peg-add-method normalize + (&rest args)
+  (let ((e (peg-normalize `(and . ,args))))
+    `(and ,e (* ,e))))
+(peg-add-method normalize opt (&rest args)
+  (let ((e (peg-normalize `(and . ,args))))
+    `(or ,e (null))))
+(peg-add-method normalize if (&rest args)
+  `(if ,(peg-normalize `(and . ,args))))
+(peg-add-method normalize not (&rest args)
+  `(not ,(peg-normalize `(and . ,args))))
+(peg-add-method normalize \` (form)
+  (peg-normalize `(stack-action ,form)))
+(peg-add-method normalize stack-action (form)
+  (unless (member '-- form)
+    (error "Malformed stack action: %S" form))
+  (let ((args (cdr (member '-- (reverse form))))
+       (values (cdr (member '-- form))))
+    (let ((form `(let ,(mapcar (lambda (var) `(,var (pop peg-stack))) args)
+                  ,@(mapcar (lambda (val) `(push ,val peg-stack)) values))))
+      `(action ,form))))
+(defvar peg-char-classes 
+  '(ascii alnum alpha blank cntrl digit graph lower multibyte nonascii print
+         punct space unibyte upper word xdigit))
+(peg-add-method normalize set (&rest specs)
+  (cond ((null specs) '(fail))
+       ((and (null (cdr specs))
+             (let ((range (peg-range-designator (car specs))))
+               (and range `(range ,(car range) ,(cdr range))))))
+       (t 
+        (let ((chars '()) (ranges '()) (classes '()))
+          (while specs
+            (let* ((spec (pop specs))
+                   (range (peg-range-designator spec)))
+              (cond (range
+                     (push range ranges))
+                    ((peg-characterp spec)
+                     (push spec chars))
+                    ((stringp spec)
+                     (setq chars (append (reverse (append spec ())) chars)))
+                    ((memq spec peg-char-classes)
+                     (push spec classes))
+                    (t (error "Invalid set specifier: %S" spec)))))
+          (setq ranges (reverse ranges))
+          (setq chars (delete-dups (reverse chars)))
+          (setq classes (reverse classes))
+          (cond ((and (null ranges) 
+                      (null classes)
+                      (cond ((null chars) '(fail))
+                            ((null (cdr chars)) `(char ,(car chars))))))
+                (t `(set ,ranges ,chars ,classes)))))))
+(defun peg-range-designator (x)
+  (and (symbolp x)
+       (let ((str (symbol-name x)))
+        (and (= (length str) 3)
+             (eq (aref str 1) ?-)
+             (< (aref str 0) (aref str 2))
+             (cons (aref str 0) (aref str 2))))))
+;; characterp is new in Emacs 23.
+(defun peg-characterp (x)
+  (if (fboundp 'characterp) 
+      (characterp x)
+    (integerp x)))
+(peg-add-method normalize list (&rest args)
+  (peg-normalize 
+   (let ((marker (make-symbol "magic-marker")))
+     `(and (stack-action (-- ',marker))
+          ,@args
+          (stack-action (-- 
+                         (let ((l '()))
+                           (while 
+                               (let ((e (pop peg-stack)))
+                                 (cond ((eq e ',marker) nil)
+                                       ((null peg-stack)
+                                        (error "Marker not longer stack"))
+                                       (t (push e l) t))))
+                           l)))))))
+(peg-add-method normalize substring (&rest args)
+  (peg-normalize 
+   `(and `(-- (point))
+        ,@args
+        `(start -- (buffer-substring-no-properties start (point))))))
+(peg-add-method normalize region (&rest args)
+  (peg-normalize 
+   `(and `(-- (point))
+        ,@args
+        `(-- (point)))))
+(peg-add-method normalize replace (pe replacement)
+  (peg-normalize
+   `(and (stack-action (-- (point)))
+        ,pe
+        (stack-action (start -- (progn
+                                  (delete-region start (point))
+                                  (insert-before-markers ,replacement))))
+        (stack-action (x --)))))
+(peg-add-method normalize quote (form)
+  (error "quote is reverved for future use"))
+(peg-define-method-table translate)
+;; This is the main translation function.
+(defun peg-translate-exp (exp)
+  "Return the ELisp code to match the PE EXP."
+  (let ((translator (or (gethash (car exp) peg-translate-methods)
+                       (error "No translator for: %S" (car exp)))))
+    (apply translator (cdr exp))))
+(peg-add-method translate and (e1 e2)
+  `(and ,(peg-translate-exp e1)
+       ,(peg-translate-exp e2)))
+(peg-add-method translate or (e1 e2)
+  (let ((cp (peg-make-choicepoint)))
+    `(,@(peg-save-choicepoint cp)
+      (or ,(peg-translate-exp e1)
+         (,@(peg-restore-choicepoint cp)
+          ,(peg-translate-exp e2))))))
+;; Choicepoints are used for backtracking.  At a choicepoint we save
+;; enough state, so that we can continue from there if needed.
+(defun peg-make-choicepoint ()
+  (cons (make-symbol "point") (make-symbol "thunks")))
+(defun peg-save-choicepoint (choicepoint)
+  `(let ((,(car choicepoint) (point))
+        (,(cdr choicepoint) peg-thunks))))
+(defun peg-restore-choicepoint (choicepoint)
+  `(progn 
+     (goto-char ,(car choicepoint))
+     (setq peg-thunks ,(cdr choicepoint))))
+;; match empty strings
+(peg-add-method translate null ()
+  `t)
+;; match nothing
+(peg-add-method translate fail ()
+  `nil)
+(peg-add-method translate bob () '(bobp))
+(peg-add-method translate eob () '(eobp))
+(peg-add-method translate eol () '(eolp))
+(peg-add-method translate bol () '(bolp))
+(peg-add-method translate bow () '(looking-at "\\<"))
+(peg-add-method translate eow () '(looking-at "\\>"))
+(peg-add-method translate bos () '(looking-at "\\_<"))
+(peg-add-method translate eos () '(looking-at "\\_>"))
+(defvar peg-syntax-classes
+  '((whitespace ?-) (word ?w) (symbol ?s) (punctuation ?.)
+    (open ?\() (close ?\)) (string ?\") (escape ?\\) (charquote ?/)
+    (math ?$) (prefix ?') (comment ?<) (endcomment ?>)
+    (comment-fence ?!) (string-fence ?|)))
+(peg-add-method translate syntax-class (class)
+  (let ((probe (assoc class peg-syntax-classes)))
+    (cond (probe `(looking-at ,(format "\\s%c" (cadr probe))))
+         (t (error "Invalid syntax class: %S\nMust be one of: %s" class
+                   (mapcar #'car peg-syntax-classes))))))
+(peg-add-method translate * (e)
+  (let ((cp (peg-make-choicepoint)))
+    `(progn (while (,@(peg-save-choicepoint cp)
+                   (cond (,(peg-translate-exp e))
+                         (t ,(peg-restore-choicepoint cp)
+                            nil))))
+           t)))
+(peg-add-method translate if (e)
+  (let ((cp (peg-make-choicepoint)))
+    `(,@(peg-save-choicepoint cp)
+      (when ,(peg-translate-exp e)
+       ,(peg-restore-choicepoint cp)
+       t))))
+(peg-add-method translate not (e)
+  (let ((cp (peg-make-choicepoint)))
+    `(,@(peg-save-choicepoint cp)
+      (when (not ,(peg-translate-exp e))
+       ,(peg-restore-choicepoint cp)
+       t))))
+(peg-add-method translate any ()
+  '(when (not (eobp))
+     (forward-char)
+     t))
+(peg-add-method translate char (c)
+  `(when (eq (char-after) ',c)
+     (forward-char)
+     t))
+(peg-add-method translate set (ranges chars classes)
+  `(when (looking-at ',(peg-make-charset-regexp ranges chars classes))
+     (forward-char)
+     t))
+(defun peg-make-charset-regexp (ranges chars classes)
+  (when (and (not ranges) (not classes) (<= (length chars) 1))
+    (error "Bug"))
+  (let ((rbracket (member ?\] chars))
+       (minus (member ?- chars))
+       (hat (member ?^ chars)))
+    (dolist (c '(?\] ?- ?^))
+      (setq chars (delete c chars)))
+    (format "[%s%s%s%s%s%s]"
+           (if rbracket "]" "")
+           (if minus "-" "")
+           (mapconcat (lambda (x) (format "%c-%c" (car x) (cdr x)))
+                      ranges "")
+           (mapconcat (lambda (c) (format "[:%s:]" c)) classes "")
+           (mapconcat (lambda (c) (format "%c" c)) chars "")
+           (if hat "^" ""))))
+(peg-add-method translate range (from to)
+  `(when (and (char-after)
+             (<= ',from (char-after))
+             (<= (char-after) ',to))
+     (forward-char)
+     t))
+(peg-add-method translate str (str)
+  `(when (looking-at ',(regexp-quote str))
+     (goto-char (match-end 0))
+     t))
+(peg-add-method translate call (name)
+  (or (gethash name peg-rules) 
+      (error "Reference to unknown rule: %S" name))
+  `(funcall ,name))
+(peg-add-method translate action (form)
+  `(progn
+     (push (cons (point) (lambda () ,form)) peg-thunks)
+     t))
+(defvar peg-stack)
+(defun peg-postprocess (thunks)
+  "Execute \"actions\"."
+  (let  ((peg-stack '()))
+    (dolist (thunk (mapcar (lambda (x)
+                            (goto-char (car x))
+                            (cons (point-marker) (cdr x)))
+                          (reverse thunks)))
+      (goto-char (car thunk))
+      (funcall (cdr thunk)))
+    (list t peg-stack)))
+;; Left recursion is presumably a common mistate when using PEGs.
+;; Here we try to detect such mistakes.  Essentailly we traverse the
+;; graph as long as we can without consuming input.  When we find a
+;; recursive call we signal an error.
+(defun peg-check-cycles (peg-rules)
+  (maphash (lambda (name exp)
+            (peg-detect-cycles exp (list name))
+            (dolist (node (peg-find-star-nodes exp))
+              (peg-detect-cycles node '())))
+          peg-rules))
+(defun peg-find-star-nodes (exp)
+  (let ((type (car exp)))
+    (cond ((memq type peg-leaf-types) '())
+         (t (let ((kids (apply #'append 
+                               (mapcar #'peg-find-star-nodes (cdr exp)))))
+              (if (eq type '*)
+                  (cons exp kids)
+                kids))))))
+(peg-define-method-table detect-cycles)
+(defun peg-detect-cycles (exp path)
+  "Signal an error on a cycle.
+Otherwise traverse EXP recursively and return T if EXP can match
+without consuming input.  Return nil if EXP definetly consumes
+input.  PATH is the list of rules that we have visited so far."
+  (apply (or (gethash (car exp) peg-detect-cycles-methods) 
+            (error "No detect-cycle method for: %S" exp))
+        path (cdr exp)))
+(peg-add-method detect-cycles call (path name)
+  (cond ((member name path)
+        (error "Possible left recursion: %s"
+               (mapconcat (lambda (x) (format "%s" x))
+                          (reverse (cons name path)) " -> ")))
+       (t
+        (peg-detect-cycles (gethash name peg-rules) (cons name path)))))
+(peg-add-method detect-cycles and (path e1 e2)
+  (and (peg-detect-cycles e1 path)
+       (peg-detect-cycles e2 path)))
+(peg-add-method detect-cycles or (path e1 e2)
+  (or (peg-detect-cycles e1 path)
+      (peg-detect-cycles e2 path)))
+(peg-add-method detect-cycles * (path e) 
+  (when (peg-detect-cycles e path)
+    (error "Infinite *-loop: %S matches empty string" e))
+  t)
+(peg-add-method detect-cycles if  (path e) (peg-unary-nullable e path))
+(peg-add-method detect-cycles not (path e) (peg-unary-nullable e path))
+(defun peg-unary-nullable (exp path)
+  (peg-detect-cycles exp path)
+  t)
+(peg-add-method detect-cycles any   (path)       nil)
+(peg-add-method detect-cycles char  (path c)     nil)
+(peg-add-method detect-cycles set   (path r c k) nil)
+(peg-add-method detect-cycles range (path c1 c2) nil)
+(peg-add-method detect-cycles str   (path s)     (equal s ""))
+(peg-add-method detect-cycles null  (path)       t)
+(peg-add-method detect-cycles fail  (path)       nil)
+(peg-add-method detect-cycles bob   (path)       t)
+(peg-add-method detect-cycles eob   (path)       t)
+(peg-add-method detect-cycles bol   (path)       t)
+(peg-add-method detect-cycles eol   (path)       t)
+(peg-add-method detect-cycles bow   (path)       t)
+(peg-add-method detect-cycles eow   (path)       t)
+(peg-add-method detect-cycles bos   (path)       t)
+(peg-add-method detect-cycles eos   (path)       t)
+(peg-add-method detect-cycles syntax-class (p n) nil)
+(peg-add-method detect-cycles action (path form) t)
+;;; Tests:
+(defmacro peg-parse-string (rules string)
+  `(with-temp-buffer 
+     (insert ,string)
+     (goto-char (point-min))
+     (peg-parse . ,rules)))
+;; We can't expand the macro at compile time, because it needs helper
+;; functions which aren't available yet.  Delay the expansion to
+;; load-time (or later).
+(eval '(progn " 
+(" ;<-- this stops Emacs from indenting the next form
+(defun peg-test ()
+  (interactive)
+  (assert (peg-parse-string ((s "a")) "a"))
+  (assert (not (peg-parse-string ((s "a")) "b")))
+  (assert (peg-parse-string ((s (not "a"))) "b"))
+  (assert (not (peg-parse-string ((s (not "a"))) "a")))
+  (assert (peg-parse-string ((s (if "a"))) "a"))
+  (assert (not (peg-parse-string ((s (if "a"))) "b")))
+  (assert (peg-parse-string ((s "ab")) "ab"))
+  (assert (not (peg-parse-string ((s "ab")) "ba")))
+  (assert (not (peg-parse-string ((s "ab")) "a")))
+  (assert (peg-parse-string ((s (range ?0 ?9))) "0"))
+  (assert (not (peg-parse-string ((s (range ?0 ?9))) "a")))
+  (assert (peg-parse-string ((s [0-9])) "0"))
+  (assert (not (peg-parse-string ((s [0-9])) "a")))
+  (assert (not (peg-parse-string ((s [0-9])) "")))
+  (assert (peg-parse-string ((s (any))) "0"))
+  (assert (not (peg-parse-string ((s (any))) "")))
+  (assert (peg-parse-string ((s (eob))) ""))
+  (assert (peg-parse-string ((s (not (eob)))) "a"))
+  (assert (peg-parse-string ((s (or "a" "b"))) "a"))
+  (assert (peg-parse-string ((s (or "a" "b"))) "b"))
+  (assert (not (peg-parse-string ((s (or "a" "b"))) "c")))
+  (assert (peg-parse-string ((s (and "a" "b"))) "ab"))
+  (assert (peg-parse-string ((s (and "a" "b"))) "abc"))
+  (assert (not (peg-parse-string ((s (and "a" "b"))) "ba")))
+  (assert (peg-parse-string ((s (and "a" "b" "c"))) "abc"))
+  (assert (peg-parse-string ((s (* "a") "b" (eob))) "b"))
+  (assert (peg-parse-string ((s (* "a") "b" (eob))) "ab"))
+  (assert (peg-parse-string ((s (* "a") "b" (eob))) "aaab"))
+  (assert (not (peg-parse-string ((s (* "a") "b" (eob))) "abc")))
+  (assert (peg-parse-string ((s "")) "abc"))
+  (assert (peg-parse-string ((s "" (eob))) ""))
+  (assert (peg-parse-string ((s (opt "a") "b")) "abc"))
+  (assert (peg-parse-string ((s (opt "a") "b")) "bc"))
+  (assert (not (peg-parse-string ((s (or))) "ab")))
+  (assert (peg-parse-string ((s (and))) "ab"))
+  (assert (peg-parse-string ((s (and))) ""))
+  (assert (peg-parse-string ((s ["^"])) "^"))
+  (assert (peg-parse-string ((s ["^a"])) "a"))
+  (assert (peg-parse-string ((s ["-"])) "-"))
+  (assert (peg-parse-string ((s ["]-"])) "]"))
+  (assert (peg-parse-string ((s ["^]"])) "^"))
+  (assert (peg-parse-string ((s [alpha])) "z"))
+  (assert (not (peg-parse-string ((s [alpha])) "0")))
+  (assert (not (peg-parse-string ((s [alpha])) "")))
+  (assert (not (peg-parse-string ((s ["][:alpha:]"])) "z")))
+  (assert (peg-parse-string ((s (bob))) ""))
+  (assert (peg-parse-string ((s (bos))) "x"))
+  (assert (not (peg-parse-string ((s (bos))) " x")))
+  (assert (peg-parse-string ((s "x" (eos))) "x"))
+  (assert (peg-parse-string ((s (syntax-class whitespace))) " "))
+  (assert (equal (peg-parse-string ((s `(-- 1 2))) "") '(t (2 1))))
+  (assert (equal (peg-parse-string ((s `(-- 1 2) `(a b -- a b))) "")
+                '(t (2 1))))
+  (assert (equal (peg-parse-string ((s (list x y))
+                                   (x `(-- 1))
+                                   (y `(-- 2)))
+                                  "")
+                '(t ((1 2)))))
+  (assert (equal (peg-parse-string ((s (list (* x)))
+                                   (x "x" `(-- 'x)))
+                                  "xxx")
+                '(t ((x x x)))))
+  (assert (equal (peg-parse-string ((s (region (* x)))
+                                   (x "x" `(-- 'x)))
+                                  "xxx")
+                '(t (4 x x x 1))))
+  (assert (equal (peg-parse-string ((s (region (list (* x))))
+                                   (x "x" `(-- 'x 'y)))
+                                  "xxx")
+                '(t (4 (x y x y x y) 1))))
+  (assert (equal (with-temp-buffer 
+                  (save-excursion (insert "abcdef"))
+                  (list
+                   (peg-parse (x "a" 
+                                 (replace "bc" "x")
+                                 (replace "de" "y")
+                                 "f"))
+                   (buffer-string)))
+                '((t nil) "axyf")))
+  )
+(when (featurep 'cl) 
+  (peg-test))
+;;; Examples:
+;; peg-ex-recognize-int recognizes integers.  An integer begins with a
+;; optional sign, then follows one or more digits.  Digits are all
+;; characters from 0 to 9.
+;; Notes: 
+;; 1) "" matches the empty sequence, i.e. matches without
+;; consuming input.  
+;; 2) [0-9] is the character range from 0 to 9.  This can also be
+;; written as (range ?0 ?9). [Note that 0-9 is a symbol.]
+(defun peg-ex-recognize-int ()
+  (peg-parse (number   sign digit (* digit))
+            (sign     (or "+" "-" ""))
+            (digit    [0-9])))
+;; peg-ex-parse-int recognizes integers and computes the corresponding
+;; value.  The grammer is the same as for `peg-ex-recognize-int' added
+;; with parsing actions.  Unfortunaletly, the actions add quite a bit
+;; of clutter.
+;; The action for the sign rule pushes t on the stack for a minus sign
+;; and nil for plus or no sign.
+;; The action for the digit rule pushes the value for a single digit.
+;; The action `(a b -- (+ (* a 10) b)), takes two items from the stack
+;; and pushes the first digit times 10 added to second digit.
+;; The action `(minus val -- (if minus (- val) val)), negates the
+;; value if the minus flag is true.
+(defun peg-ex-parse-int ()
+  (peg-parse (number sign
+                    digit
+                    (* digit `(a b -- (+ (* a 10) b)))
+                    `(minus val -- (if minus (- val) val)))
+            (sign (or (and "+" `(-- nil))
+                      (and "-" `(-- t))
+                      (and "" `(-- nil))))
+            (digit [0-9] `(-- (- (char-before) ?0)))))
+;; Put point after the ) and press C-x C-e
+;; (peg-ex-parse-int)-234234
+;; Parse arithmetic expressions and compute the result as side effect.
+(defun peg-ex-arith ()
+  (peg-parse 
+   (expr (or (and ws sum eol)
+            (and (* (not eol) (any)) eol error)))
+   (sum product (* (or (and plus product `(a b -- (+ a b)))
+                      (and minus product `(a b -- (- a b))))))
+   (product value (* (or (and times value `(a b -- (* a b)))
+                        (and divide value `(a b -- (/ a b))))))
+   (value (or (and (substring number) `(string -- (string-to-number string)))
+             (and open sum close)))
+   (number (+ [0-9]) ws)
+   (plus "+" ws)
+   (minus "-" ws)
+   (times "*" ws)
+   (divide "/" ws)
+   (open "(" ws)
+   (close ")" ws)
+   (ws (* (or " " "\t")))
+   (eol (or "\n" "\r\n" "\r"))
+   (error (action (error "Parse error at: %s" (point))))))
+;; (peg-ex-arith)   1 + 2 * 3 * (4 + 5)
+;; Parse URI according to RFC 2396.
+(defun peg-ex-uri ()
+  (peg-parse
+   (URI-reference (or absoluteURI relativeURI) 
+                 (or (and "#" (substring fragment))
+                     `(-- nil))
+                 `(scheme user host port path query fragment -- 
+                          (list :scheme scheme :user user
+                                :host host :port port
+                                :path path :query query 
+                                :fragment fragment)))
+   (absoluteURI (substring scheme) ":" (or hier-part opaque-part))
+   (hier-part ;(-- user host port path query)
+    (or net-path 
+       (and `(-- nil nil nil)
+            abs-path))
+    (or (and "?" (substring query))
+       `(-- nil)))
+   (net-path "//" authority (or abs-path `(-- nil)))
+   (abs-path "/" path-segments)
+   (path-segments segment (list (* "/" segment)) `(s l -- (cons s l)))
+   (segment (substring (* pchar) (* ";" param)))
+   (param (* pchar))
+   (pchar (or unreserved escaped [":@&=+$,"]))
+   (query (* uric))
+   (fragment (* uric))
+   (relativeURI (or net-path abs-path rel-path) (opt "?" query))
+   (rel-path rel-segment (opt abs-path))
+   (rel-segment (+ unreserved escaped [";@&=+$,"]))
+   (authority (or server reg-name))
+   (server (or (and (or (and (substring userinfo) "@")
+                       `(-- nil))
+                   hostport)
+              `(-- nil nil nil)))
+   (userinfo (* (or unreserved escaped [";:&=+$,"])))
+   (hostport (substring host) (or (and ":" (substring port))
+                                 `(-- nil)))
+   (host (or hostname ipv4address))
+   (hostname (* domainlabel ".") toplabel (opt "."))
+   (domainlabel alphanum
+               (opt (* (or alphanum "-") (if alphanum))
+                    alphanum))
+   (toplabel alpha
+            (* (or alphanum "-") (if alphanum))
+            alphanum)
+   (ipv4address (+ digit) "." (+ digit) "." (+ digit) "." (+ digit))
+   (port (* digit))
+   (scheme alpha (* (or alpha digit ["+-."])))
+   (reg-name (or unreserved escaped ["$,;:@&=+"]))
+   (opaque-part uric-no-slash (* uric))
+   (uric (or reserved unreserved escaped))
+   (uric-no-slash (or unreserved escaped [";?:@&=+$,"]))
+   (reserved (set ";/?:@&=+$,"))
+   (unreserved (or alphanum mark))
+   (escaped "%" hex hex)
+   (hex (or digit [A-F] [a-f]))
+   (mark (set "-_.!~*'()"))
+   (alphanum (or alpha digit))
+   (alpha (or lowalpha upalpha))
+   (lowalpha [a-z])
+   (upalpha [A-Z])
+   (digit [0-9])))
+;; (peg-ex-uri)file:/bar/baz.html?foo=df#x
+;; (peg-ex-uri)http://address@hidden:8080/bar/baz.html?x=1#foo
+;; Parse a lisp style Sexp.
+;; [To keep the example short, ' and . are handled as ordinary symbol.]
+(defun peg-ex-lisp ()
+  (peg-parse 
+   (sexp _ (or string list number symbol))
+   (_ (* (or [" \n\t"] comment)))
+   (comment ";" (* (not (or "\n" (eob))) (any)))
+   (string "\"" (substring  (* (not "\"") (any))) "\"")
+   (number (substring (opt (set "+-")) (+ digit))
+          (if terminating)
+          `(string -- (string-to-number string)))
+   (symbol (substring (and symchar (* (not terminating) symchar)))
+          `(s -- (intern s)))
+   (symchar [a-z A-Z 0-9 "-;!#%&'*+,./:;<=>address@hidden|}~"])
+   (list "("           `(-- (cons nil nil)) `(hd -- hd hd)
+        (* sexp        `(tl e -- (setcdr tl (list e)))
+           ) _ ")"     `(hd tl -- (cdr hd)))
+   (digit [0-9])
+   (terminating (or (set " \n\t();\"'") (eob)))))
+;; (peg-ex-lisp)
+;; We try to detect left recursion and report it as error.
+(defun peg-ex-left-recursion ()
+  (eval '(peg-parse (exp (or term
+                            (and exp "+" exp)))
+                   (term (or digit
+                             (and term "*" term)))
+                   (digit [0-9]))))
+(defun peg-ex-infinite-loop ()
+  (eval '(peg-parse (exp (* (or "x"
+                               "y"
+                               (action (foo))))))))
+)) ; end of eval-when-load
+(provide 'peg)
+;;; peg.el ends here

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