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 <https://www.gnu.org/licenses/>.
20 ;; Authors: Austin Clements <aclements@csail.mit.edu>
26 (defun notmuch-sexp-create-parser ()
27 "Return a new streaming S-expression parser.
29 This parser is designed to incrementally read an S-expression
30 whose structure is known to the caller. Like a typical
31 S-expression parsing interface, it provides a function to read a
32 complete S-expression from the input. However, it extends this
33 with an additional function that requires the next value in the
34 input to be a list and descends into it, allowing its elements to
35 be read one at a time or further descended into. Both functions
36 can return 'retry to indicate that not enough input is available.
38 The parser always consumes input from point in the current
39 buffer. Hence, the caller is allowed to delete any data before
40 point and may resynchronize after an error by moving point."
42 (vector 'notmuch-sexp-parser
45 ;; Partial parse position marker
47 ;; Partial parse state
50 (defmacro notmuch-sexp--depth (sp) `(aref ,sp 1))
51 (defmacro notmuch-sexp--partial-pos (sp) `(aref ,sp 2))
52 (defmacro notmuch-sexp--partial-state (sp) `(aref ,sp 3))
54 (defun notmuch-sexp-read (sp)
55 "Consume and return the value at point in the current buffer.
57 Returns 'retry if there is insufficient input to parse a complete
58 value (though it may still move point over whitespace). If the
59 parser is currently inside a list and the next token ends the
60 list, this moves point just past the terminator and returns 'end.
61 Otherwise, this moves point to just past the end of the value and
64 (skip-chars-forward " \n\r\t")
67 ;; We've reached the end of a list
68 (if (= (notmuch-sexp--depth sp) 0)
69 ;; .. but we weren't in a list. Let read signal the
70 ;; error to be consistent with all other code paths.
71 (read (current-buffer))
72 ;; Go up a level and return an end token
73 (decf (notmuch-sexp--depth sp))
77 ;; We're at the beginning of a list. If we haven't started
78 ;; a partial parse yet, attempt to read the list in its
79 ;; entirety. If this fails, or we've started a partial
80 ;; parse, extend the partial parse to figure out when we
81 ;; have a complete list.
83 (when (null (notmuch-sexp--partial-state sp))
84 (let ((start (point)))
86 (throw 'return (read (current-buffer)))
87 (end-of-file (goto-char start)))))
88 ;; Extend the partial parse
91 (let* ((new-state (parse-partial-sexp
92 (or (notmuch-sexp--partial-pos sp) (point))
94 (notmuch-sexp--partial-state sp)))
95 ;; A complete value is available if we've
97 (depth (first new-state)))
100 ;; Reset partial parse state
101 (setf (notmuch-sexp--partial-state sp) nil
102 (notmuch-sexp--partial-pos sp) nil
104 ;; Update partial parse state
105 (setf (notmuch-sexp--partial-state sp) new-state
106 (notmuch-sexp--partial-pos sp) (point-marker)))))
108 (read (current-buffer))
111 ;; Attempt to read a non-compound value
112 (let ((start (point)))
114 (let ((val (read (current-buffer))))
115 ;; We got what looks like a complete read, but if
116 ;; we reached the end of the buffer in the process,
117 ;; we may not actually have all of the input we
118 ;; need (unless it's a string, which is delimited).
119 (if (or (stringp val) (not (eobp)))
121 ;; We can't be sure the input was complete
128 (defun notmuch-sexp-begin-list (sp)
129 "Parse the beginning of a list value and enter the list.
131 Returns 'retry if there is insufficient input to parse the
132 beginning of the list. If this is able to parse the beginning of
133 a list, it moves point past the token that opens the list and
134 returns t. Later calls to `notmuch-sexp-read' will return the
135 elements inside the list. If the input in buffer is not the
136 beginning of a list, throw invalid-read-syntax."
138 (skip-chars-forward " \n\r\t")
139 (cond ((eobp) 'retry)
140 ((= (char-after) ?\()
142 (incf (notmuch-sexp--depth sp))
145 ;; Skip over the bad character like `read' does
147 (signal 'invalid-read-syntax (list (string (char-before)))))))
149 (defun notmuch-sexp-eof (sp)
150 "Signal an error if there is more data in SP's buffer.
152 Moves point to the beginning of any trailing data or to the end
153 of the buffer if there is only trailing whitespace."
155 (skip-chars-forward " \n\r\t")
157 (error "Trailing garbage following expression")))
159 (defvar notmuch-sexp--parser nil
160 "The buffer-local notmuch-sexp-parser instance.
162 Used by `notmuch-sexp-parse-partial-list'.")
164 (defvar notmuch-sexp--state nil
165 "The buffer-local `notmuch-sexp-parse-partial-list' state.")
167 (defun notmuch-sexp-parse-partial-list (result-function result-buffer)
168 "Incrementally parse an S-expression list from the current buffer.
170 This function consumes an S-expression list from the current
171 buffer, applying RESULT-FUNCTION in RESULT-BUFFER to each
172 complete value in the list. It operates incrementally and should
173 be called whenever the input buffer has been extended with
174 additional data. The caller just needs to ensure it does not
175 move point in the input buffer."
177 ;; Set up the initial state
178 (unless (local-variable-p 'notmuch-sexp--parser)
179 (set (make-local-variable 'notmuch-sexp--parser)
180 (notmuch-sexp-create-parser))
181 (set (make-local-variable 'notmuch-sexp--state) 'begin))
184 (case notmuch-sexp--state
187 (if (eq (notmuch-sexp-begin-list notmuch-sexp--parser) 'retry)
189 (setq notmuch-sexp--state 'result)))
192 (let ((result (notmuch-sexp-read notmuch-sexp--parser)))
194 (retry (setq done t))
195 (end (setq notmuch-sexp--state 'end))
196 (t (with-current-buffer result-buffer
197 (funcall result-function result))))))
199 ;; Any trailing data is unexpected
200 (notmuch-sexp-eof notmuch-sexp--parser)
202 ;; Clear out what we've parsed
203 (delete-region (point-min) (point)))
205 (provide 'notmuch-parser)
208 ;; byte-compile-warnings: (not cl-functions)
211 ;;; notmuch-parser.el ends here