/interpreter/tags/at2dist091109/src/edu/vub/at/objects/natives/grammar/AGBegin.java
Java | 132 lines | 64 code | 15 blank | 53 comment | 6 complexity | f7f9c833fc4a00211f1034a74ce138a4 MD5 | raw file
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}