Simplify inspection of matched sequences

[Cory Dodt]

I need to capture the parsed text for certain cases. For example, in the template language I'm (re-)implementing:

"[foo]bar"

The first token [foo] is expanded to the value of the template named 'foo', if it exists. If it doesn't, it's supposed to expand to the literal string '[foo]'.

Here's a test and an implementation. In this test, a2 returns both a return value 'cd' and the original matched text.

    def test_matchToCursor(self):
        in2 = "ab[cd]ef"
        g = """aa ::= ('a' 'b' => 'ab'):a1 <a2>:a2 ('e' 'f' => 'ef'):a3 <end> => a1,a2,a3
            a2 ::= <pos>:p1 '[' 'c' 'd' ']' => 'cd', ''.join(self.matchToCursor(p1))
            """
        MyGrammar = style2.EnhancedGrammar.makeGrammar(g, {}, "MyGrammar")
        parser = MyGrammar(in2)
        actual = parser.apply('aa')
        expected = ('ab', ('cd', '[cd]'), 'ef')
        self.assertEqual(actual, expected)

        in1 = ["ab", ["c", "d"], "ef"]
        g = """aa ::= "ab":a1 <a2>:a2 "ef":a3 <end> => a1,a2,a3
            a2 ::= <pos>:p1 [ "c" "d" ] => 'cd', self.matchToCursor(p1)
            """
        MyGrammar2 = style2.EnhancedGrammar.makeGrammar(g, {}, "MyGrammar2")
        parser = MyGrammar2(in1)
        actual = parser.apply('aa')
        expected = ('ab', ('cd', [['c', 'd']]), 'ef')
        self.assertEqual(actual, expected)

and style2.EnhancedGrammar looks like this:

class EnhancedGrammar(OMeta):
    def rule_pos(self):
        """
        Return the position the cursor is currently at
        """
        return self.input.position

    def matchToCursor(self, startpos):
        """
        Return the sequence beginning at startpos and ending at the current
        input cursor
        """
        return self.input.data[startpos:self.input.position]