+;;; peg.el --- Parsing Expression Grammars in Emacs Lisp
+;;
+;; Copyright 2008 Helmut Eller <eller.hel...@gmail.com>.
+;;
+;; Version: 0.4 (2008-Dec-17)
+;;
+;; This file is licensed under the terms of the GNU General Public
+;; License as distributed with Emacs (press C-h C-c for details).
+;;
+;;; 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". For
+;; convenience, PE is implicitly wrapped in a and. 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]
+;;
+;; `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.
+;;
+;; 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)))))
+
+(eval-and-compile
+ (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 eob
+ set))
+
+(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 *list (&rest args)
+ (peg-normalize `(list (* . ,args))))
+
+(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 eob ()
+ '(eobp))
+
+(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 eob (path) t)
+(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 (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://lu...@www.foo.com: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 "-;!#%&'*+,./:;<=>?...@[]^_`{|}~"])
+ (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
projects / m17n / m17n-lib-cs.git / commitdiff