/interpreter/tags/at2dist091109/src/edu/vub/at/objects/natives/grammar/AGUnquote.java

 1/**
 2 * AmbientTalk/2 Project
 3 * AGUnquote.java created on 26-jul-2006 at 16:29:32
 4 * (c) Programming Technology Lab, 2006 - 2007
 5 * Authors: Tom Van Cutsem & Stijn Mostinckx
 6 * 
 7 * Permission is hereby granted, free of charge, to any person
 8 * obtaining a copy of this software and associated documentation
 9 * files (the "Software"), to deal in the Software without
10 * restriction, including without limitation the rights to use,
11 * copy, modify, merge, publish, distribute, sublicense, and/or
12 * sell copies of the Software, and to permit persons to whom the
13 * Software is furnished to do so, subject to the following
14 * conditions:
15 *
16 * The above copyright notice and this permission notice shall be
17 * included in all copies or substantial portions of the Software.
18 *
19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
26 * OTHER DEALINGS IN THE SOFTWARE.
27 */
28package edu.vub.at.objects.natives.grammar;
29
30import edu.vub.at.exceptions.InterpreterException;
31import edu.vub.at.exceptions.XIllegalUnquote;
32import edu.vub.at.objects.ATContext;
33import edu.vub.at.objects.ATObject;
34import edu.vub.at.objects.grammar.ATExpression;
35import edu.vub.at.objects.grammar.ATUnquote;
36import edu.vub.at.objects.natives.NATText;
37
38import java.util.HashSet;
39import java.util.Set;
40
41/**
42 * The native implementation of an unquotation AG element.
43 * Example: <tt>#(x+1)</tt>
44 *
45 * @author tvcutsem
46 */
47public class AGUnquote extends AGExpression implements ATUnquote {
48
49	protected final ATExpression unqExp_;
50	
51	public AGUnquote(ATExpression exp) {
52		unqExp_ = exp;
53	}
54	
55	public ATExpression base_expression() { return unqExp_; }
56
57	/**
58	 * An unquotation cannot be evaluated, but rather gives rise to an XIllegalUnquote exception.
59	 * This is because an unquotation should always be nested within a quotation.
60	 * 
61	 * AGUNQ(exp).eval(ctx) = ERROR
62	 */
63	public ATObject meta_eval(ATContext ctx) throws InterpreterException {
64		throw new XIllegalUnquote(unqExp_);
65	}
66
67	/**
68	 * Quoting an unquotation means evaluating its contained expression, and returning
69	 * its value as the result of the quote.
70	 */
71	public ATObject meta_quote(ATContext ctx) throws InterpreterException {
72		return unqExp_.meta_eval(ctx);
73	}
74
75	public NATText meta_print() throws InterpreterException {
76		return NATText.atValue("#("+ unqExp_.meta_print().javaValue + ")");
77	}
78	
79	/**
80	 * FV(#exp) = FV(exp)
81	 */
82	public Set impl_freeVariables() throws InterpreterException {
83		return unqExp_.impl_freeVariables();
84	}
85	
86	/**
87	 * Turn unquotation back into quotation.
88	 * E.g. `(x + #(y)) => y is considered a free variable
89	 */
90	public Set impl_quotedFreeVariables() throws InterpreterException {
91		return this.impl_freeVariables();
92	}
93	
94}