1 ;; notmuch-parser.el --- streaming S-expression parser
3 ;; Copyright © Austin Clements
5 ;; This file is part of Notmuch.
7 ;; Notmuch is free software: you can redistribute it and/or modify it
8 ;; under the terms of the GNU General Public License as published by
9 ;; the Free Software Foundation, either version 3 of the License, or
10 ;; (at your option) any later version.
12 ;; Notmuch is distributed in the hope that it will be useful, but
13 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
14 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 ;; General Public License for more details.
17 ;; You should have received a copy of the GNU General Public License
18 ;; along with Notmuch. If not, see <http://www.gnu.org/licenses/>.
20 ;; Authors: Austin Clements <aclements@csail.mit.edu>
24 (defun notmuch-sexp-create-parser ()
25 "Return a new streaming S-expression parser.
27 This parser is designed to incrementally read an S-expression
28 whose structure is known to the caller. Like a typical
29 S-expression parsing interface, it provides a function to read a
30 complete S-expression from the input. However, it extends this
31 with an additional function that requires the next value in the
32 input to be a list and descends into it, allowing its elements to
33 be read one at a time or further descended into. Both functions
34 can return 'retry to indicate that not enough input is available.
36 The parser always consumes input from point in the current
37 buffer. Hence, the caller is allowed to delete any data before
38 point and may resynchronize after an error by moving point."
40 (vector 'notmuch-sexp-parser
43 ;; Partial parse position marker
45 ;; Partial parse state
48 (defmacro notmuch-sexp--depth (sp) `(aref ,sp 1))
49 (defmacro notmuch-sexp--partial-pos (sp) `(aref ,sp 2))
50 (defmacro notmuch-sexp--partial-state (sp) `(aref ,sp 3))
52 (defun notmuch-sexp-read (sp)
53 "Consume and return the value at point in the current buffer.
55 Returns 'retry if there is insufficient input to parse a complete
56 value (though it may still move point over whitespace). If the
57 parser is currently inside a list and the next token ends the
58 list, this moves point just past the terminator and returns 'end.
59 Otherwise, this moves point to just past the end of the value and
62 (skip-chars-forward " \n\r\t")
65 ;; We've reached the end of a list
66 (if (= (notmuch-sexp--depth sp) 0)
67 ;; .. but we weren't in a list. Let read signal the
68 ;; error to be consistent with all other code paths.
69 (read (current-buffer))
70 ;; Go up a level and return an end token
71 (decf (notmuch-sexp--depth sp))
75 ;; We're at the beginning of a list. If we haven't started
76 ;; a partial parse yet, attempt to read the list in its
77 ;; entirety. If this fails, or we've started a partial
78 ;; parse, extend the partial parse to figure out when we
79 ;; have a complete list.
81 (when (null (notmuch-sexp--partial-state sp))
82 (let ((start (point)))
84 (throw 'return (read (current-buffer)))
85 (end-of-file (goto-char start)))))
86 ;; Extend the partial parse
89 (let* ((new-state (parse-partial-sexp
90 (or (notmuch-sexp--partial-pos sp) (point))
92 (notmuch-sexp--partial-state sp)))
93 ;; A complete value is available if we've
95 (depth (first new-state)))
98 ;; Reset partial parse state
99 (setf (notmuch-sexp--partial-state sp) nil
100 (notmuch-sexp--partial-pos sp) nil
102 ;; Update partial parse state
103 (setf (notmuch-sexp--partial-state sp) new-state
104 (notmuch-sexp--partial-pos sp) (point-marker)))))
106 (read (current-buffer))
109 ;; Attempt to read a non-compound value
110 (let ((start (point)))
112 (let ((val (read (current-buffer))))
113 ;; We got what looks like a complete read, but if
114 ;; we reached the end of the buffer in the process,
115 ;; we may not actually have all of the input we
116 ;; need (unless it's a string, which is delimited).
117 (if (or (stringp val) (not (eobp)))
119 ;; We can't be sure the input was complete
126 (defun notmuch-sexp-begin-list (sp)
127 "Parse the beginning of a list value and enter the list.
129 Returns 'retry if there is insufficient input to parse the
130 beginning of the list. If this is able to parse the beginning of
131 a list, it moves point past the token that opens the list and
132 returns t. Later calls to `notmuch-sexp-read' will return the
133 elements inside the list. If the input in buffer is not the
134 beginning of a list, throw invalid-read-syntax."
136 (skip-chars-forward " \n\r\t")
137 (cond ((eobp) 'retry)
138 ((= (char-after) ?\()
140 (incf (notmuch-sexp--depth sp))
143 ;; Skip over the bad character like `read' does
145 (signal 'invalid-read-syntax (list (string (char-before)))))))
147 (defun notmuch-sexp-eof (sp)
148 "Signal an error if there is more data in SP's buffer.
150 Moves point to the beginning of any trailing data or to the end
151 of the buffer if there is only trailing whitespace."
153 (skip-chars-forward " \n\r\t")
155 (error "Trailing garbage following expression")))
157 (defvar notmuch-sexp--parser nil
158 "The buffer-local notmuch-sexp-parser instance.
160 Used by `notmuch-sexp-parse-partial-list'.")
162 (defvar notmuch-sexp--state nil
163 "The buffer-local `notmuch-sexp-parse-partial-list' state.")
165 (defun notmuch-sexp-parse-partial-list (result-function result-buffer)
166 "Incrementally parse an S-expression list from the current buffer.
168 This function consumes an S-expression list from the current
169 buffer, applying RESULT-FUNCTION in RESULT-BUFFER to each
170 complete value in the list. It operates incrementally and should
171 be called whenever the input buffer has been extended with
172 additional data. The caller just needs to ensure it does not
173 move point in the input buffer."
175 ;; Set up the initial state
176 (unless (local-variable-p 'notmuch-sexp--parser)
177 (set (make-local-variable 'notmuch-sexp--parser)
178 (notmuch-sexp-create-parser))
179 (set (make-local-variable 'notmuch-sexp--state) 'begin))
182 (case notmuch-sexp--state
185 (if (eq (notmuch-sexp-begin-list notmuch-sexp--parser) 'retry)
187 (setq notmuch-sexp--state 'result)))
190 (let ((result (notmuch-sexp-read notmuch-sexp--parser)))
192 (retry (setq done t))
193 (end (setq notmuch-sexp--state 'end))
194 (t (with-current-buffer result-buffer
195 (funcall result-function result))))))
197 ;; Any trailing data is unexpected
198 (notmuch-sexp-eof notmuch-sexp--parser)
200 ;; Clear out what we've parsed
201 (delete-region (point-min) (point)))
203 (provide 'notmuch-parser)
206 ;; byte-compile-warnings: (not cl-functions)