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1 | ;;; -*-lisp-*- |
2 | ;;; | |
3 | ;;; Parsers for expressions with binary operators | |
4 | ;;; | |
5 | ;;; (c) 2009 Straylight/Edgeware | |
6 | ;;; | |
7 | ||
8 | ;;;----- Licensing notice --------------------------------------------------- | |
9 | ;;; | |
e0808c47 | 10 | ;;; This file is part of the Sensible Object Design, an object system for C. |
dea4d055 MW |
11 | ;;; |
12 | ;;; SOD is free software; you can redistribute it and/or modify | |
13 | ;;; it under the terms of the GNU General Public License as published by | |
14 | ;;; the Free Software Foundation; either version 2 of the License, or | |
15 | ;;; (at your option) any later version. | |
16 | ;;; | |
17 | ;;; SOD is distributed in the hope that it will be useful, | |
18 | ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | ;;; GNU General Public License for more details. | |
21 | ;;; | |
22 | ;;; You should have received a copy of the GNU General Public License | |
23 | ;;; along with SOD; if not, write to the Free Software Foundation, | |
24 | ;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
25 | ||
26 | (cl:in-package #:sod-parser) | |
27 | ||
28 | ;;;-------------------------------------------------------------------------- | |
29 | ;;; Basic protocol. | |
30 | ||
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31 | (export 'operator-push-action) |
32 | (defgeneric operator-push-action (left right) | |
33 | (:documentation | |
34 | "Determine relative precedence between LEFT and RIGHT operators. | |
35 | ||
36 | Returns one of three possible values: | |
37 | ||
38 | * `:push' means to push the RIGHT operator onto the stack, above the | |
39 | LEFT operator -- i.e., RIGHT has higher precedence than LEFT. | |
40 | ||
41 | * `:apply' means to apply the LEFT operator to arguments immediately | |
42 | and try again, comparing RIGHT to the new topmost operator -- i.e., | |
43 | LEFT has higher precedence than RIGHT. | |
44 | ||
45 | * `:error' means that the situation is erroneous: a continuable error is | |
46 | signalled and the situation resolved by applying the LEFT operator and | |
47 | then pushing the RIGHT one -- i.e., treating them as having similar | |
48 | precedence and left associativity). | |
49 | ||
50 | There is a default method which decides between `:push' and `:apply' by | |
51 | comparing numerical precedence values.")) | |
52 | ||
53 | (export 'expr) | |
54 | (defparse expr ((&key (nestedp (gensym "NESTEDP-"))) | |
55 | operand binop preop postop) | |
bf090e02 MW |
56 | "Parse an expression involving unary and binary operators. |
57 | ||
58 | Within the parsers for operands and operators, the variable NESTEDP is | |
59 | bound to a generalized boolean which is true if an unmatched open- | |
60 | parenthesis has been seen. | |
61 | ||
62 | The OPERAND parser should produce a value; the various operator parsers | |
63 | (BINOP, PREOP, and POSTOP) should produce objects obeying the `operator' | |
64 | protocol. The final output of the `expr' parse is the result of | |
65 | evaluating the parsed expression. (Of course, the definition of | |
66 | `evaluation' here is determined entirely by the methods on | |
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67 | `apply-operator', so the final value may be a parse tree, for example.) |
68 | ||
69 | Alternatively, the BINOP, PREOP, and POSTOP parsers may be /lists/ of | |
70 | parsers (distinguished because the head of a parser form is expected to be | |
71 | an atom). These are implicitly `or'red together. Within such a list, a | |
72 | parser form beginning `:op' is given special interpretation. The syntax | |
73 | is expected to be | |
74 | ||
75 | (:op MAKE-OP RECOG &rest ARGS) | |
76 | ||
77 | which has the following effects: | |
78 | ||
79 | * around the expression parser, the expression | |
80 | ||
81 | (MAKE-OP . ARGS) | |
82 | ||
83 | is evaluated once and the result stashed away; and | |
84 | ||
85 | * a parser of the form | |
86 | ||
87 | (seq (RECOG) OP) | |
88 | ||
89 | is added as one of the alternatives of the disjunction, where OP is the | |
90 | cached operator built in the first step." | |
bf090e02 | 91 | |
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92 | (flet ((wrap (parser) |
93 | `(parser (,nestedp) | |
94 | (declare (ignorable ,nestedp)) | |
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95 | ,parser)) |
96 | (hack-oplist (oplist) | |
97 | (if (or (atom oplist) (atom (car oplist))) (values nil oplist) | |
98 | (let ((binds nil) (ops nil)) | |
99 | (dolist (op oplist) | |
100 | (if (and (consp op) (eq (car op) :op)) | |
101 | (destructuring-bind | |
102 | (recog make-op &rest args) (cdr op) | |
103 | (with-gensyms (var) | |
104 | (push `(,var (,make-op ,@args)) binds) | |
105 | (push `(seq ((nil ,recog)) ,var) ops))) | |
106 | (push op ops))) | |
107 | (values (nreverse binds) `(or ,@(nreverse ops))))))) | |
108 | (multiple-value-bind (binvars binops) (hack-oplist binop) | |
109 | (multiple-value-bind (prevars preops) (hack-oplist preop) | |
110 | (multiple-value-bind (postvars postops) (hack-oplist postop) | |
111 | `(let (,@binvars ,@prevars ,@postvars) | |
112 | (parse-expression ,(wrap operand) | |
113 | ,(wrap binops) | |
114 | ,(wrap preops) | |
115 | ,(wrap postops)))))))) | |
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116 | |
117 | ;;;-------------------------------------------------------------------------- | |
118 | ;;; Numerical precedence. | |
119 | ||
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120 | (export '(operator-left-precedence operator-right-precedence |
121 | operator-associativity)) | |
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122 | (defgeneric operator-left-precedence (operator) |
123 | (:documentation | |
124 | "Return the OPERATOR's left-precedence. | |
125 | ||
126 | Higher precedence numbers indicate tighter leftward binding. Under the | |
127 | default method for `operator-push-action', the OPERATOR's left precedence | |
128 | is compared to the existing operators' right precedences to determine the | |
129 | parser's behaviour: if it is higher, then the OPERATOR is pushed; | |
130 | otherwise the existing operator is applied. Thus, equal precedences cause | |
131 | left-associative parsing.")) | |
132 | (defgeneric operator-right-precedence (operator) | |
133 | (:documentation | |
134 | "Return the OPERATOR's right-precedence. | |
135 | ||
136 | Higher precedence numbers indicate tighter rightward binding. Under the | |
137 | default method for `operator-push-action', a new operator's left | |
bf090e02 | 138 | precedence may be compared to the existing OPERATOR's right precedences to |
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139 | determine the parser's behaviour: if it is higher, then the new operator |
140 | is pushed; otherwise the existing OPERATOR is applied. Thus, equal | |
141 | precedences cause left-associative parsing.")) | |
142 | ||
143 | (defgeneric operator-associativity (operator) | |
144 | (:documentation | |
145 | "Returns an OPERATOR's associativity, as a symbol. | |
146 | ||
147 | The return value is one of `:left', `:right' or `nil'. If two adjacent | |
148 | operators have the same precedence, their associativities are compared. | |
149 | If both associativities are `:left' then the left-hand operator is | |
150 | considered to have higher precedence; if both are `:right' then the | |
151 | right-hand operator is considered to have higher precedence. If they're | |
152 | inconsistent or `nil', then an error is reported and the behaviour is as | |
153 | if both were `:left'.") | |
154 | (:method (operator) :left)) | |
155 | ||
156 | ;;;-------------------------------------------------------------------------- | |
157 | ;;; Basic operator protocol. | |
158 | ||
159 | (export 'prefix-operator) | |
160 | (defclass prefix-operator () | |
161 | () | |
162 | (:documentation | |
163 | "Prefix operator base class. | |
164 | ||
165 | Prefix operators are special because they are pushed at a time when the | |
166 | existing topmost operator on the stack may not have its operand | |
167 | available. It is therefore incorrect to attempt to apply any existing | |
122cd950 | 168 | operators without careful checking.")) |
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169 | |
170 | (export 'simple-operator) | |
171 | (defclass simple-operator () | |
4b8e5c03 | 172 | ((%function :initarg :function :reader operator-function) |
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173 | (name :initarg :name :initform "<unnamed operator>" |
174 | :reader operator-name)) | |
175 | (:documentation | |
176 | "A simple operator applies a FUNCTION to arguments when it is applied. | |
177 | ||
178 | The precise details of the function are left to subclasses to sort out.")) | |
179 | ||
180 | (export 'simple-unary-operator) | |
181 | (defclass simple-unary-operator (simple-operator) | |
182 | () | |
183 | (:documentation | |
184 | "A unary operator works on the topmost value on the value stack. | |
185 | ||
186 | The topmost item is popped, the FUNCTION is applied to it, and the result | |
187 | is pushed back on.")) | |
188 | ||
189 | (export 'simple-binary-operator) | |
190 | (defclass simple-binary-operator (simple-operator) | |
191 | ((lprec :initarg :left-precedence :initarg :precedence | |
192 | :reader operator-left-precedence) | |
193 | (rprec :initarg :right-precedence :reader operator-right-precedence) | |
194 | (associativity :initarg :associative :initform :left | |
195 | :reader operator-associativity)) | |
196 | (:documentation | |
197 | "A binary operator works on the two topmost values on the value stack. | |
198 | ||
199 | The function's arguments are the two topmost items in /reverse/ order -- | |
200 | so the topmost item is second. This is usually what you want. | |
201 | ||
202 | The left and right precedences are settable independently. Usually (and | |
203 | this is the default) you will set them equal, and use the `:associativity' | |
204 | initarg to determine associativity; however, right-associativity can also | |
205 | be obtained by setting the right-precedence lower than the left. Special | |
206 | effects can be obtained by setting them in other ways. Use your | |
207 | imagination.")) | |
208 | ||
209 | (export 'simple-postfix-operator) | |
210 | (defclass simple-postfix-operator (simple-unary-operator) | |
211 | ((lprec :initarg :left-precedence :initarg :precedence | |
212 | :reader operator-left-precedence) | |
213 | (rprec :initarg :right-precedence :reader operator-right-precedence)) | |
214 | (:documentation | |
215 | "A postfix operator is applied to a single operand. | |
216 | ||
217 | The left and right precedences are settable independently. Usually you | |
218 | will want to set them equal (this is the default) and quite high. Special | |
219 | effects can be obtained by doing other things instead; but note that you | |
220 | will get an incorrect parse if the right precedence is lower than the left | |
221 | precedence of a binary operator because the postfix operator will be | |
222 | applied to the result of the binary operator.")) | |
223 | ||
224 | (export 'simple-prefix-operator) | |
225 | (defclass simple-prefix-operator (prefix-operator simple-unary-operator) | |
226 | ((rprec :initarg :precedence :reader operator-right-precedence)) | |
227 | (:documentation | |
228 | "A prefix operator is applied to a single operand. | |
229 | ||
230 | There is only one precedence value for a prefix operator: the | |
231 | `prefix-operator' superclass arranges that the left precedence is | |
232 | effectively minus infinity.")) | |
233 | ||
234 | (export 'preop) | |
235 | (defmacro preop (name (x prec) &body body) | |
bf090e02 MW |
236 | "Define a prefix operator. |
237 | ||
238 | The operator will be called NAME in error messages, and have right | |
239 | precedence PREC. To apply the operator, BODY is evaluated with X bound to | |
240 | the operand." | |
241 | ||
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242 | `(make-instance 'simple-prefix-operator |
243 | :name ,name | |
244 | :precedence ,prec | |
245 | :function (lambda (,x) ,@body))) | |
246 | ||
247 | (export 'postop) | |
248 | (defmacro postop (name (x prec &key rprec) &body body) | |
bf090e02 MW |
249 | "Define a postfix operator. |
250 | ||
251 | The operator will be called NAME in error messages, and have left | |
252 | precedence PREC and right precendence RPREC (defaulting to PREC). To | |
253 | apply the operator, BODY is evaluated with X bound to the operand." | |
254 | ||
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255 | (once-only (name prec rprec) |
256 | `(make-instance 'simple-postfix-operator | |
257 | :name ,name | |
258 | :left-precedence ,prec | |
259 | :right-precedence ,(or rprec prec) | |
260 | :function (lambda (,x) ,@body)))) | |
261 | ||
262 | (export 'binop) | |
263 | (defmacro binop (name (x y prec &key rprec (assoc :left)) &body body) | |
bf090e02 MW |
264 | "Define a binary operator. |
265 | ||
266 | The operator will be called NAME in error messages, and have left | |
267 | precedence PREC and right precedence RPREC (defaulting to PREC, implying | |
268 | left associativity under the default `operator-push-action' | |
269 | implementation. To apply the operator, BODY is evaluated with X and Y | |
270 | bound to the operands in the order they were parsed" | |
271 | ||
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272 | (once-only (name prec rprec assoc) |
273 | `(make-instance 'simple-binary-operator | |
274 | :name ,name | |
275 | :left-precedence ,prec | |
276 | :right-precedence ,(or rprec prec) | |
277 | :associative ,assoc | |
278 | :function (lambda (,x ,y) ,@body)))) | |
279 | ||
280 | ;;;-------------------------------------------------------------------------- | |
281 | ;;; Parentheses. | |
282 | ||
283 | (defclass parenthesis () | |
284 | ((tag :initarg :tag :initform nil)) | |
285 | (:documentation | |
286 | "Base class for parenthesis operators.")) | |
287 | ||
288 | (export 'open-parenthesis) | |
289 | (defclass open-parenthesis (parenthesis prefix-operator) ()) | |
290 | ||
291 | (export 'close-parenthesis) | |
292 | (defclass close-parenthesis (parenthesis) ()) | |
293 | ||
294 | (export '(lparen rparen)) | |
295 | (defun lparen (tag) | |
296 | (make-instance 'open-parenthesis :tag tag)) | |
297 | (defun rparen (tag) | |
298 | (make-instance 'close-parenthesis :tag tag)) | |
299 | ||
300 | ;;;----- That's all, folks -------------------------------------------------- |