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

  1/**
  2 * AmbientTalk/2 Project
  3 * AGBegin.java created on 26-jul-2006 at 12:26:48
  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.eval.Evaluator;
 31import edu.vub.at.exceptions.InterpreterException;
 32import edu.vub.at.exceptions.XTypeMismatch;
 33import edu.vub.at.objects.ATAbstractGrammar;
 34import edu.vub.at.objects.ATContext;
 35import edu.vub.at.objects.ATObject;
 36import edu.vub.at.objects.ATTable;
 37import edu.vub.at.objects.grammar.ATBegin;
 38import edu.vub.at.objects.grammar.ATStatement;
 39import edu.vub.at.objects.mirrors.NativeClosure;
 40import edu.vub.at.objects.natives.NATNumber;
 41import edu.vub.at.objects.natives.NATText;
 42
 43import java.util.HashSet;
 44import java.util.Set;
 45
 46/**
 47 * AGBegin represents the abstract grammar element of a list of statements.
 48 * Examples:
 49 *  <tt>a ; b ; c</tt>
 50 *  
 51 * @author tvcutsem
 52 */
 53public final class AGBegin extends NATAbstractGrammar implements ATBegin {
 54	
 55	private final ATTable statements_;
 56	
 57	// contains a cached version of the expression's free variables
 58	private Set freeVars_;
 59	
 60	public AGBegin(ATTable statements) {
 61	  statements_ = statements;
 62	}
 63	
 64	/**
 65	 * AGBEGIN encapsulates a sequence of statements and evaluates each of these statements in turn.
 66	 * The return value is the value of the last statement.
 67	 * 
 68	 * AGBEGIN([statement | statements]).eval(ctx) = statement.eval(ctx) ; BEGIN(statements).eval(ctx)
 69	 * AGBEGIN([statement]).eval(ctx) = statement.eval(ctx)
 70	 * 
 71	 * Note that this implementation of begin is *not* tail-recursive.
 72	 * Tail-recursion is made impossible because Java will not allow a return
 73	 * to the caller until the last expression is also evaluated. Tail-recursion optimalisation
 74	 * requires a minimal form of explicit continuations.
 75	 */
 76	public ATObject meta_eval(ATContext ctx) throws InterpreterException {
 77		NATNumber siz = statements_.base_length().asNativeNumber();
 78		int lastIdx = siz.javaValue;
 79		if (lastIdx == 0) {
 80			return Evaluator.getNil();
 81		}
 82		for (int i = 1; i < lastIdx; i++) {
 83			statements_.base_at(NATNumber.atValue(i)).meta_eval(ctx);
 84		}
 85		return statements_.base_at(NATNumber.atValue(lastIdx)).meta_eval(ctx);
 86	}
 87
 88	/**
 89	 * AGBEGIN(statements*).quote(ctx) = AGBEGIN((statements*).quote(ctx))
 90	 */
 91	public ATObject meta_quote(ATContext ctx) throws InterpreterException {
 92		return new AGBegin(statements_.meta_quote(ctx).asTable());
 93	}
 94	
 95	public ATTable base_statements() { return statements_; }
 96	
 97	public NATText meta_print() throws InterpreterException {
 98		return Evaluator.printAsStatements(statements_);
 99	}
100	
101	public ATBegin asBegin() throws XTypeMismatch {
102		return this;
103	}
104	
105	/**
106	 * FV({ stmt1; stmt2; ... }) = FV(stmt1) U FV(stmt2) U ... \ (IV(stmt1) U IV(stmt2) U ...) }
107	 */
108	public Set impl_freeVariables() throws InterpreterException {
109		if (freeVars_ == null) {
110			freeVars_ = new HashSet();
111			final Set boundVars = new HashSet();
112			statements_.base_each_(new NativeClosure(this) {
113				public ATObject base_apply(ATTable args) throws InterpreterException {
114					ATAbstractGrammar stmt = this.get(args, 1).asAbstractGrammar();
115					freeVars_.addAll(stmt.impl_freeVariables());
116					if (stmt.isDefinition()) {
117						boundVars.addAll(stmt.asDefinition().impl_introducedVariables());					
118					}
119					return stmt;
120				}
121			});
122			freeVars_.removeAll(boundVars);
123		}
124		return freeVars_;
125	}
126	
127	
128	public Set impl_quotedFreeVariables() throws InterpreterException {
129		return statements_.impl_quotedFreeVariables();
130	}
131
132}