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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.millscript.expr.Expr;
24  
25  /**
26   * The PostfixSyntaxInterface interface should be implemented by any class which
27   * provides a piece of postfix syntax. Postfix syntax is that which specifically
28   * follows the expression it operates on, but it may also preceed an additional
29   * expression. e.g. explode syntax vs. append syntax.
30   *
31   * <p>
32   * Postfix syntax also has the concept of precedence, which allows the parser to
33   * utomatically glue syntax together. e.g. in the following:
34   * <code>
35   * x := arg.func + 7;
36   * </code>
37   * means assign the result of adding 7 to the result of calling
38   * <code>func</code> with argument <code>arg</code> to variable <code>x</code>.
39   * The parser can automatically interpret this becuase <code>.</code> has a
40   * higher precedence than <code>+</code>, which in turn has a higher precedence
41   * than <code>:=</code>.
42   * </p>
43   */
44  public interface PostfixSyntaxInterface {
45  
46      /**
47       * Returns the precedence of this piece of postfix syntax. Higher values
48       * represent more tightly bound syntax.
49       *
50       * @return  the precedence of this postfix syntax
51       */
52      int getPrecedence();
53  
54      /**
55       * Parse the syntax for the specified symbol, using the specified
56       * <code>Parser</code>. The symbol is specified because different symbols
57       * may share the same syntax, but result in slightly different expressions.
58       * The <code>Parser</code> is supplied as the source to parse from. As this
59       * is postfix syntax, we are also supplied the expression on the left hand
60       * side of the symbol along with the current precedence we should parse to.
61       *
62       * @param   sym     the symbol to parse this syntax for
63       * @param   prec    the current precedence we should parse to
64       * @param   lhs     the expression on the left hand side of the specified
65       *                  symbol
66       * @param   parser  Parser to parse from, i.e. the source to parse from
67       * @return  an expression for this syntax
68       */
69      Expr postfix( final String sym, final int prec, final Expr lhs, final Parser parser );
70  
71  }