1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
|
;;;; grammars.lisp
(in-package #:argot)
;;; GRAMMAR & RULES
(defstruct rule lhs pattern action check)
(defclass grammar ()
((rules
:accessor grammar-rules
:initform (make-hash-table :test #'eq))
(start
:accessor start-rule
:initarg :start-rule
:initform (error "START-RULE is required")
:type symbol)
(documentation
:reader grammar-documentation
:initarg :documentation
:initform "")))
(defun include-rule (grammar rule)
(setf (gethash (rule-lhs rule) (grammar-rules grammar)) rule))
;;; PARSING
(defvar *position*)
(defvar *grammar*)
(defvar *tokens*)
(defvar *bindings*)
(defun succeed (result)
(values result t))
(defun fail ()
(values nil nil))
(defparameter +eof+ #())
(defun next-token ()
(if (< *position* (length *tokens*))
(prog1 (elt *tokens* *position*)
(incf *position*))
+eof+))
(defun update-bindings (var value)
(setf *bindings* (acons var value *bindings*)))
(defmacro try-parse
((&optional (result (gensym)))
parse-expression
&optional
(success-clause `(succeed ,result))
(fail-clause '(fail)))
(alexandria:with-gensyms (successp pos)
`(let ((,pos *position*))
(multiple-value-bind (,result ,successp) ,parse-expression
(if ,successp ,success-clause
(progn
(setf *position* ,pos)
,fail-clause))))))
(defmacro if-parse
((&optional (result (gensym)))
parse-expression
&optional
(success-clause `(succeed ,result))
(fail-clause '(fail)))
(alexandria:with-gensyms (successp)
`(multiple-value-bind (,result ,successp) ,parse-expression
(if ,successp ,success-clause
,fail-clause))))
(defun parse-sequence (patterns)
"Parse each member of PATTERNS and succeed with a list of results. If
any pattern fails the whole parse fails."
(loop :for pattern :in patterns
:for (result successp)
:= (multiple-value-list (parse-pattern pattern))
:if successp
:collect result :into results
:else :return (fail)
:finally (return (succeed results))))
(defun parse-optional (pattern)
(try-parse
(res) (parse-pattern pattern)
(succeed res)
(succeed nil)))
(defun parse-kleene (pattern)
(loop :for (res successp) := (multiple-value-list (try-parse () (parse-pattern pattern)))
:while successp :collect res :into results
:finally (return-from parse-kleene (succeed results))))
(defun parse-one-or-more (pattern)
(if-parse (first) (parse-pattern pattern)
(if-parse (rest) (parse-kleene pattern)
(succeed (cons first rest)))))
(defun parse-alternatives (patterns)
(if (endp patterns) (fail)
(try-parse (result) (parse-pattern (first patterns))
(succeed result)
(parse-alternatives (rest patterns)))))
(defun literals->patterns (literals)
(loop :for l :in literals :collect (list := l)))
(defun literals-equal? (a b) (eq a b))
(defun parse-literal (literal)
(if (literals-equal? (next-token) literal)
(succeed literal)
(fail)))
(defun parse-literal-alternatives (literals)
(parse-alternatives (literals->patterns literals)))
(defun parse-kleene-literal (literal)
(parse-kleene (list := literal)))
(defun parse-one-or-more-literal (literal)
(parse-one-or-more (list := literal)))
(defun parse-optional-literal (literal)
(parse-optional (list := literal)))
(defun parse-literal-sequence (literals)
(parse-sequence (literals->patterns literals)))
(defun parse-binding-pattern (var pattern)
(if-parse
(result) (parse-pattern pattern)
(progn
(update-bindings var result)
(succeed result))))
(defun parse-item ()
(let ((token (next-token)))
(if (not (eq token +eof+))
(succeed token)
(fail))))
(defun parse-eof ()
(if (eq +eof+ (next-token))
(succeed nil)
(fail)))
(defun find-grammar (name)
(and (symbolp name)
(boundp name)
(let ((val (symbol-value name)))
(and (typep val 'grammar)
val))))
(defun parse-grammar-pattern (language)
(if-parse (subtokens) (parse-item)
(if (listp subtokens)
(if-let (grammar (find-grammar language))
(let ((*grammar* grammar)
(*position* 0)
(*tokens* (coerce subtokens 'vector)))
(parse-rule (start-rule grammar)))
(error "No grammar called ~s" language))
(fail))))
(defun parse-pattern (pattern)
(if (nonterminal? pattern)
(parse-rule pattern)
(destructuring-bind (op . args) pattern
(case op
(:seq (parse-sequence args))
(:? (parse-optional (first args)))
(:* (parse-kleene (first args)))
(:+ (parse-one-or-more (first args)))
(:or (parse-alternatives args))
(:or= (parse-literal-alternatives args))
(:= (parse-literal (first args)))
(:*= (parse-kleene-literal (first args)))
(:+= (parse-one-or-more-literal (first args)))
(:?= (parse-optional-literal (first args)))
(:seq= (parse-literal-sequence args))
(:@ (parse-binding-pattern (first args) (second args)))
(:{} (parse-grammar-pattern (first args)))
(:item (parse-item))
(:eof (parse-eof))))))
(defun handle-post-rule (rule result)
(with-slots (lhs check action) rule
(let ((bindings (acons lhs result *bindings*)))
(when check
(unless (funcall check bindings)
(return-from handle-post-rule (fail))))
(if action
(succeed (funcall action bindings))
(succeed result)))))
(defun parse-rule (nonterminal)
(if-let (rule (gethash nonterminal (grammar-rules *grammar*)))
(let ((*bindings* nil))
(if-parse (result) (parse-pattern (rule-pattern rule))
(handle-post-rule rule result)))
(fail)))
(define-condition argot-parse-error (error)
((position :initarg :position)
(input :initarg :input))
(:report (lambda (err stream)
(with-slots (position input) err
(let ((pos (max 0 (- position 2))))
(format
stream
"Parse failed at position ~a, around:~%~a"
pos (print-seq-range-pointing-at-center input pos 4)))))))
(defun listslice (seq start stop)
(coerce (alexandria-2:subseq* seq start stop) 'list))
(defun print-seq-range-pointing-at-center (items position radius)
(let* ((front
(format nil "... ~{~s~^ ~}" (listslice items (max 0 (- position radius)) position )))
(line
(format nil "~a ~{~s~^ ~} ..."
front (listslice items position (+ position radius 1)))))
(concatenate
'string
line (list #\Newline)
(loop :repeat (1+ (length front)) :collect #\Space)
"^" (list #\Newline))))
(defun parse (grammar tokens)
(let ((*position* 0)
(*grammar* grammar)
(*tokens* (coerce tokens 'vector)))
(multiple-value-bind (result successp) (parse-rule (start-rule *grammar*))
(unless successp
(error 'argot-parse-error
:position *position*
:input *tokens*))
result)))
|
