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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 | ||
31 | (export 'push-operator) | |
32 | (defgeneric push-operator (operator state) | |
33 | (:documentation | |
34 | "Push an OPERATOR onto the STATE's operator stack. | |
35 | ||
36 | This should apply existing stacked operators as necessary to obey the | |
37 | language's precedence rules.")) | |
38 | ||
bf090e02 | 39 | (export 'push-value) |
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40 | (defgeneric push-value (value state) |
41 | (:documentation | |
42 | "Push VALUE onto the STATE's value stack. | |
43 | ||
268f7777 | 44 | The default method just does that without any fuss. It's unlikely that |
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45 | this will need changing unless you invent some really weird values.")) |
46 | ||
47 | (export 'apply-operator) | |
48 | (defgeneric apply-operator (operator state) | |
49 | (:documentation | |
50 | "Apply the OPERATOR to argument on the STATE's value stack. | |
51 | ||
52 | This should pop any necessary arguments, and push the result.")) | |
53 | ||
54 | (export 'operator-push-action) | |
55 | (defgeneric operator-push-action (left right) | |
56 | (:documentation | |
57 | "Determine relative precedence between LEFT and RIGHT operators. | |
58 | ||
59 | Returns one of three possible values: | |
60 | ||
61 | * `:push' means to push the RIGHT operator onto the stack, above the | |
62 | LEFT operator -- i.e., RIGHT has higher precedence than LEFT. | |
63 | ||
64 | * `:apply' means to apply the LEFT operator to arguments immediately | |
65 | and try again, comparing RIGHT to the new topmost operator -- i.e., | |
66 | LEFT has higher precedence than RIGHT. | |
67 | ||
68 | * `:error' means that the situation is erroneous: a continuable error is | |
69 | signalled and the situation resolved by applying the LEFT operator and | |
70 | then pushing the RIGHT one -- i.e., treating them as having similar | |
71 | precedence and left associativity). | |
72 | ||
73 | There is a default method which decides between `:push' and `:apply' by | |
74 | comparing numerical precedence values.")) | |
75 | ||
76 | (export 'expr) | |
77 | (defparse expr ((&key (nestedp (gensym "NESTEDP-"))) | |
78 | operand binop preop postop) | |
bf090e02 MW |
79 | "Parse an expression involving unary and binary operators. |
80 | ||
81 | Within the parsers for operands and operators, the variable NESTEDP is | |
82 | bound to a generalized boolean which is true if an unmatched open- | |
83 | parenthesis has been seen. | |
84 | ||
85 | The OPERAND parser should produce a value; the various operator parsers | |
86 | (BINOP, PREOP, and POSTOP) should produce objects obeying the `operator' | |
87 | protocol. The final output of the `expr' parse is the result of | |
88 | evaluating the parsed expression. (Of course, the definition of | |
89 | `evaluation' here is determined entirely by the methods on | |
90 | `apply-operator', so the final value may be a parse tree, for example.)" | |
91 | ||
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92 | (flet ((wrap (parser) |
93 | `(parser (,nestedp) | |
94 | (declare (ignorable ,nestedp)) | |
95 | ,parser))) | |
96 | `(parse-expression ,(wrap operand) | |
97 | ,(wrap binop) | |
98 | ,(wrap preop) | |
99 | ,(wrap postop)))) | |
100 | ||
101 | ;;;-------------------------------------------------------------------------- | |
102 | ;;; Numerical precedence. | |
103 | ||
104 | (export '(operator-left-precedence operator-right-precedence)) | |
105 | (defgeneric operator-left-precedence (operator) | |
106 | (:documentation | |
107 | "Return the OPERATOR's left-precedence. | |
108 | ||
109 | Higher precedence numbers indicate tighter leftward binding. Under the | |
110 | default method for `operator-push-action', the OPERATOR's left precedence | |
111 | is compared to the existing operators' right precedences to determine the | |
112 | parser's behaviour: if it is higher, then the OPERATOR is pushed; | |
113 | otherwise the existing operator is applied. Thus, equal precedences cause | |
114 | left-associative parsing.")) | |
115 | (defgeneric operator-right-precedence (operator) | |
116 | (:documentation | |
117 | "Return the OPERATOR's right-precedence. | |
118 | ||
119 | Higher precedence numbers indicate tighter rightward binding. Under the | |
120 | default method for `operator-push-action', a new operator's left | |
bf090e02 | 121 | precedence may be compared to the existing OPERATOR's right precedences to |
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122 | determine the parser's behaviour: if it is higher, then the new operator |
123 | is pushed; otherwise the existing OPERATOR is applied. Thus, equal | |
124 | precedences cause left-associative parsing.")) | |
125 | ||
126 | (defgeneric operator-associativity (operator) | |
127 | (:documentation | |
128 | "Returns an OPERATOR's associativity, as a symbol. | |
129 | ||
130 | The return value is one of `:left', `:right' or `nil'. If two adjacent | |
131 | operators have the same precedence, their associativities are compared. | |
132 | If both associativities are `:left' then the left-hand operator is | |
133 | considered to have higher precedence; if both are `:right' then the | |
134 | right-hand operator is considered to have higher precedence. If they're | |
135 | inconsistent or `nil', then an error is reported and the behaviour is as | |
136 | if both were `:left'.") | |
137 | (:method (operator) :left)) | |
138 | ||
139 | ;;;-------------------------------------------------------------------------- | |
140 | ;;; Basic operator protocol. | |
141 | ||
142 | (export 'prefix-operator) | |
143 | (defclass prefix-operator () | |
144 | () | |
145 | (:documentation | |
146 | "Prefix operator base class. | |
147 | ||
148 | Prefix operators are special because they are pushed at a time when the | |
149 | existing topmost operator on the stack may not have its operand | |
150 | available. It is therefore incorrect to attempt to apply any existing | |
151 | operators without careful checking. This class provides a method on | |
152 | `push-operator' which immediately pushes the new operator without | |
153 | inspecting the existing stack.")) | |
154 | ||
155 | (export 'simple-operator) | |
156 | (defclass simple-operator () | |
4b8e5c03 | 157 | ((%function :initarg :function :reader operator-function) |
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158 | (name :initarg :name :initform "<unnamed operator>" |
159 | :reader operator-name)) | |
160 | (:documentation | |
161 | "A simple operator applies a FUNCTION to arguments when it is applied. | |
162 | ||
163 | The precise details of the function are left to subclasses to sort out.")) | |
164 | ||
165 | (export 'simple-unary-operator) | |
166 | (defclass simple-unary-operator (simple-operator) | |
167 | () | |
168 | (:documentation | |
169 | "A unary operator works on the topmost value on the value stack. | |
170 | ||
171 | The topmost item is popped, the FUNCTION is applied to it, and the result | |
172 | is pushed back on.")) | |
173 | ||
174 | (export 'simple-binary-operator) | |
175 | (defclass simple-binary-operator (simple-operator) | |
176 | ((lprec :initarg :left-precedence :initarg :precedence | |
177 | :reader operator-left-precedence) | |
178 | (rprec :initarg :right-precedence :reader operator-right-precedence) | |
179 | (associativity :initarg :associative :initform :left | |
180 | :reader operator-associativity)) | |
181 | (:documentation | |
182 | "A binary operator works on the two topmost values on the value stack. | |
183 | ||
184 | The function's arguments are the two topmost items in /reverse/ order -- | |
185 | so the topmost item is second. This is usually what you want. | |
186 | ||
187 | The left and right precedences are settable independently. Usually (and | |
188 | this is the default) you will set them equal, and use the `:associativity' | |
189 | initarg to determine associativity; however, right-associativity can also | |
190 | be obtained by setting the right-precedence lower than the left. Special | |
191 | effects can be obtained by setting them in other ways. Use your | |
192 | imagination.")) | |
193 | ||
194 | (export 'simple-postfix-operator) | |
195 | (defclass simple-postfix-operator (simple-unary-operator) | |
196 | ((lprec :initarg :left-precedence :initarg :precedence | |
197 | :reader operator-left-precedence) | |
198 | (rprec :initarg :right-precedence :reader operator-right-precedence)) | |
199 | (:documentation | |
200 | "A postfix operator is applied to a single operand. | |
201 | ||
202 | The left and right precedences are settable independently. Usually you | |
203 | will want to set them equal (this is the default) and quite high. Special | |
204 | effects can be obtained by doing other things instead; but note that you | |
205 | will get an incorrect parse if the right precedence is lower than the left | |
206 | precedence of a binary operator because the postfix operator will be | |
207 | applied to the result of the binary operator.")) | |
208 | ||
209 | (export 'simple-prefix-operator) | |
210 | (defclass simple-prefix-operator (prefix-operator simple-unary-operator) | |
211 | ((rprec :initarg :precedence :reader operator-right-precedence)) | |
212 | (:documentation | |
213 | "A prefix operator is applied to a single operand. | |
214 | ||
215 | There is only one precedence value for a prefix operator: the | |
216 | `prefix-operator' superclass arranges that the left precedence is | |
217 | effectively minus infinity.")) | |
218 | ||
219 | (export 'preop) | |
220 | (defmacro preop (name (x prec) &body body) | |
bf090e02 MW |
221 | "Define a prefix operator. |
222 | ||
223 | The operator will be called NAME in error messages, and have right | |
224 | precedence PREC. To apply the operator, BODY is evaluated with X bound to | |
225 | the operand." | |
226 | ||
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227 | `(make-instance 'simple-prefix-operator |
228 | :name ,name | |
229 | :precedence ,prec | |
230 | :function (lambda (,x) ,@body))) | |
231 | ||
232 | (export 'postop) | |
233 | (defmacro postop (name (x prec &key rprec) &body body) | |
bf090e02 MW |
234 | "Define a postfix operator. |
235 | ||
236 | The operator will be called NAME in error messages, and have left | |
237 | precedence PREC and right precendence RPREC (defaulting to PREC). To | |
238 | apply the operator, BODY is evaluated with X bound to the operand." | |
239 | ||
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240 | (once-only (name prec rprec) |
241 | `(make-instance 'simple-postfix-operator | |
242 | :name ,name | |
243 | :left-precedence ,prec | |
244 | :right-precedence ,(or rprec prec) | |
245 | :function (lambda (,x) ,@body)))) | |
246 | ||
247 | (export 'binop) | |
248 | (defmacro binop (name (x y prec &key rprec (assoc :left)) &body body) | |
bf090e02 MW |
249 | "Define a binary operator. |
250 | ||
251 | The operator will be called NAME in error messages, and have left | |
252 | precedence PREC and right precedence RPREC (defaulting to PREC, implying | |
253 | left associativity under the default `operator-push-action' | |
254 | implementation. To apply the operator, BODY is evaluated with X and Y | |
255 | bound to the operands in the order they were parsed" | |
256 | ||
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257 | (once-only (name prec rprec assoc) |
258 | `(make-instance 'simple-binary-operator | |
259 | :name ,name | |
260 | :left-precedence ,prec | |
261 | :right-precedence ,(or rprec prec) | |
262 | :associative ,assoc | |
263 | :function (lambda (,x ,y) ,@body)))) | |
264 | ||
265 | ;;;-------------------------------------------------------------------------- | |
266 | ;;; Parentheses. | |
267 | ||
268 | (defclass parenthesis () | |
269 | ((tag :initarg :tag :initform nil)) | |
270 | (:documentation | |
271 | "Base class for parenthesis operators.")) | |
272 | ||
273 | (export 'open-parenthesis) | |
274 | (defclass open-parenthesis (parenthesis prefix-operator) ()) | |
275 | ||
276 | (export 'close-parenthesis) | |
277 | (defclass close-parenthesis (parenthesis) ()) | |
278 | ||
279 | (export '(lparen rparen)) | |
280 | (defun lparen (tag) | |
281 | (make-instance 'open-parenthesis :tag tag)) | |
282 | (defun rparen (tag) | |
283 | (make-instance 'close-parenthesis :tag tag)) | |
284 | ||
285 | ;;;----- That's all, folks -------------------------------------------------- |