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|
;;; pl --- Combinator parsing library for Emacs, similar to Haskell's Parsec
;; Copyright (C) 2010-2015 Free Software Foundation, Inc.
;; Author: John Wiegley <jwiegley@gmail.com>
;; Created: 19 Mar 2015
;; Keywords: languages, lisp, internal, parsing, indentation
;; 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 2, 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
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING. If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;; The compatibility version of this library for Emacsen pre-25 will
;; be maintained at https://github.com/jwiegley/emacs-pl
;; This is a parsing library in the spirit of Haskell's parsec.
;; There are a few parsers, whose job is to inspect whatever is at the current
;; buffer position, and return zero or more details regarding what was found:
;; pl-ch Match a single character
;; pl-str Match a string
;; pl-re Match a regular expression
;; pl-num Match an integer or floating-point number
;; Other possibilities include: inspecting text properties, overlays, etc.
;; If the parser succeeds, it returns the object matched (a string by default),
;; and advances point to the next position after the match. Keywords may be
;; given to return other details:
;; :beg Beginning of the match
;; :end End of the match
;; :group N A particular regexp group
;; :props All properties within the matched region
;; :nil Return `nil` (same as using `ignore`)
;; If a parser fails, it throws the exception `failed`. This is caught by the
;; macro `pl-try`, which returns `nil` upon encountering the exception. This
;; makes it possible to build certain combinators out of these few parts:
;; pl-or Return result from first successful parser
;; pl-and Return last result, if all parsers succeed
;; pl-until If the parse fails, advance cursor position by
;; one character and try again. Keywords can
;; change the advance amount.
;; Note that even though a parse may fail, and thus return no value, any
;; side-effects that occur during the course of the parse will of course be
;; retained. This can be used to good effect, by continuing an action for as
;; long as a parse succeeds:
;; (pl-parse
;; (while t
;; (delete-region (pl-str "<xml>" :beg)
;; (pl-until
;; (pl-str "</xml>" :end)))))
;; This will delete blocks demarcated by `<xml>` and `</xml>`, for as long as
;; such blocks continue to occur contiguously to one another.
(eval-when-compile (require 'cl-lib))
(defgroup pl nil
"Combinator parsing library for Emacs, similar to Haskell's Parsec"
:group 'development)
(defun pl-ch (ch &rest args)
(if (char-equal (char-after) ch)
(prog1
(cond
((memq :nil args) nil)
((memq :beg args)
(point))
((memq :end args)
(1+ (point)))
(t
(char-to-string ch)))
(forward-char 1))
(throw 'failed nil)))
(defun pl-re (regexp &rest args)
(if (looking-at regexp)
(prog1
(cond
((memq :nil args) nil)
((memq :beg args)
(match-beginning 0))
((memq :end args)
(match-end 0))
((memq :group args)
(let ((group
(loop named outer for arg on args
when (eq (car arg) :group) do
(return-from outer (cadr arg)))))
(if group
(match-string group)
(error "Unexpected regexp :group %s" group))))
(t
(match-string 0)))
(goto-char (match-end 0)))
(throw 'failed nil)))
(defsubst pl-str (str &rest args)
(pl-re (regexp-quote str)))
(defsubst pl-num (num &rest args)
(pl-re (regexp-quote (number-to-string num))))
(defmacro pl-or (&rest parsers)
(let ((outer-sym (make-symbol "outer"))
(parser-sym (make-symbol "parser")))
`(loop named ,outer-sym for ,parser-sym in ',parsers
finally (throw 'failed nil) do
(catch 'failed
(return-from ,outer-sym (eval ,parser-sym))))))
(defmacro pl-try (&rest forms)
`(catch 'failed ,@forms))
(defalias 'pl-and 'progn)
(defalias 'pl-parse 'pl-try
"Evaluate some FORMS that define the grammar and act on it.
FORMS are simply S-expressions that typically get evaluated in
the current buffer. For example:
(pl-parse
(delete-region (pl-str \"<xml>\" :beg)
(pl-until
(pl-str \"</xml>\" :end))))
For other constructs, such as returning the result of every
parser as a list, just combine parsers with regular Lisp
forms (`pl-parse' is just a synonym for `pl-try'):
(pl-parse
(list (pl-str \"Hello\") (pl-str \"World\")))
")
(defmacro pl-until (parser &optional &key skip)
`(catch 'done
(while (not (eobp))
(catch 'failed
(throw 'done ,parser))
,(if skip
`(,skip 1)
`(forward-char 1)))))
(defmacro pl-many (&rest parsers)
(let ((final-sym (make-symbol "final"))
(result-sym (make-symbol "result"))
(parsers-sym (make-symbol "parsers")))
`(let ((,parsers-sym ',parsers)
,result-sym
,final-sym)
(while (and ,parsers-sym
(setq ,result-sym
(catch 'failed
(list (eval (car ,parsers-sym))))))
(push (car ,result-sym) ,final-sym)
(setq ,parsers-sym (cdr ,parsers-sym)))
(nreverse ,final-sym))))
(provide 'pl)
;;; pl.el ends here
|
