1 ////////////////////////////////////////////////////////////////////////////////
2 // MillScript: an Open Spice interpreter and batch website creation tool
3 // Copyright (C) 2001-2004 Open World Ltd
4 //
5 // This file is part of MillScript.
6 //
7 // MillScript is free software; you can redistribute it and/or modify it under
8 // the terms of the GNU General Public License as published by the Free
9 // Software Foundation; either version 2 of the License, or (at your option)
10 // any later version.
11 //
12 // MillScript is distributed in the hope that it will be useful, but WITHOUT
13 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
15 // more details.
16 //
17 // You should have received a copy of the GNU General Public License along with
18 // MillScript; if not, write to the Free Software Foundation, Inc., 59 Temple
19 // Place, Suite 330, Boston, MA 02111-1307 USA
20 ////////////////////////////////////////////////////////////////////////////////
21 package org.millscript.millscript.syntax;
22
23 import org.millscript.commons.util.EList;
24 import org.millscript.commons.util.list.ELinkedList;
25 import org.millscript.millscript.expr.CaseExpr;
26 import org.millscript.millscript.expr.Expr;
27 import org.millscript.millscript.expr.SwitchExpr;
28
29 /**
30 * This class implements <code>switch</code> syntax. This is used to implement
31 * switch statements in MillScript.
32 *
33 * <p>
34 * <code>switch <expr> [ tests ] endswitch</code>
35 * </p>
36 *
37 * <p>
38 * The switch statement expression must return a single result, which can be
39 * tested by specifying some optional tests. Each test is a {@link CaseExpr},
40 * e.g
41 * </p>
42 *
43 * <p>
44 * <code>case <expr> [ case <expr> ] then <expr></code>
45 * </p>
46 *
47 * <p>
48 * Each <code>case</code> statement contains an expression whose result will be
49 * compared to the <code>switch</code> statement expression result. The body of
50 * the <code>case</code> statement will be executed if the <code>case</code>
51 * statement expression result matches the switch statement expression result.
52 * If you have several <code>case</code>s that need to share the same body, you
53 * can repeat as many <code>case</code> statements as you require before the
54 * <code>then</code>.
55 * </p>
56 *
57 * @see SwitchExpr
58 */
59 public final class SwitchSyntax extends PrefixSyntax {
60
61 /**
62 * @see org.millscript.millscript.syntax.PrefixSyntaxInterface#prefix(java.lang.String, org.millscript.millscript.syntax.Parser)
63 */
64 @Override
65 public SwitchExpr prefix( final String sym, final Parser parser ) {
66 // Read the switch expression
67 Expr sexpr = parser.readExpr();
68 // This list will hold the individual case expressions
69 EList< CaseExpr > cases = new ELinkedList< CaseExpr >();
70 // Placeholder for the optional default expression
71 Expr def = null;
72 // Keep reading until the end of the switch statement
73 while ( !parser.tryRead( "endswitch" ) ) {
74 // The switch body can only contain "else" or "case" expressions
75 if ( parser.tryRead( "else" ) ) {
76 // Read the default expression/statements
77 def = parser.readStmnts();
78 } else {
79 // This list will hold individual cases that share the same body
80 // expression
81 EList< Expr > c = new ELinkedList< Expr >();
82 // We must read "case"
83 parser.mustRead( "case" );
84 // Read the case expression and add it to the list
85 c.addLast( parser.readExpr() );
86 // Continue to try and read any further case expressions that
87 // will share the same body
88 while ( parser.tryRead( "case" ) ) {
89 // There is another "case", so read it and add it to the
90 // list
91 c.addLast( parser.readExpr() );
92 }
93 // There are no more cases this body, so we must read "then"
94 parser.mustRead( "then" );
95 // Read the body statements for this case
96 Expr dexpr = parser.readStmnts();
97 // Add this new case expression to the switch statement
98 cases.addLast( new CaseExpr( c, dexpr ) );
99 }
100 }
101 // Return a new switch expression for the parsed switch, case and
102 // default expressions.
103 return new SwitchExpr( sexpr, cases, def );
104 }
105
106 }