Using the codetree class

The codetree class implements a generic parser that can parse source code (or similarly structured input) and create an XML tree representing the code. The class can also take that XML tree and write it back out as code.

A grammar must be specified to parse the input. Grammars are defined in an XML format based on EBNF with a few extensions. Each grammar is composed of definitions, each of which defines a nonterminal. Definitions may contain terminals, nonterminals, alternations, repetitions, concatenations, and other constructs.

The codetreegrammar class extends xmldom and provides codetree-specific optimizations for working with grammars.

The following example defines a simple grammar for basic math expressions (numbers and addition), parses the string "12+34", prints the resulting tree, and writes the tree back out as code.

#include <rudiments/codetree.h>
#include <rudiments/domnode.h>
#include <rudiments/stringbuffer.h>
#include <rudiments/stdio.h>

// helper function to print a code tree
static void printtree(domnode *node, int indent) {

	for (domnode *n=node->getFirstTagChild();
			!n->isNullNode();
			n=n->getNextTagSibling()) {

		for (int i=0; i<indent; i++) {
			stdoutput.write("  ");
		}
		stdoutput.printf("%s",n->getName());

		const char	*value=n->getAttributeValue("value");
		if (value) {
			stdoutput.printf(": %s",value);
		}
		stdoutput.write('\n');

		printtree(n,indent+1);
	}
}

int main(int argc, const char **argv) {

	codetree	ct;

	// define a simple grammar for basic math expressions
	// (numbers and addition)
	const char	*grammar=
		"<grammar>"
		"  <definition name=\"expression\">"
		"    <concatenation>"
		"      <nonterminal name=\"number\"/>"
		"      <repetition min=\"0\">"
		"        <concatenation>"
		"          <terminal value=\"+\"/>"
		"          <nonterminal name=\"number\"/>"
		"        </concatenation>"
		"      </repetition>"
		"    </concatenation>"
		"  </definition>"
		"  <definition name=\"number\" type=\"literal\">"
		"    <repetition min=\"1\">"
		"      <alternation>"
		"        <terminal value=\"0\"/>"
		"        <terminal value=\"1\"/>"
		"        <terminal value=\"2\"/>"
		"        <terminal value=\"3\"/>"
		"        <terminal value=\"4\"/>"
		"        <terminal value=\"5\"/>"
		"        <terminal value=\"6\"/>"
		"        <terminal value=\"7\"/>"
		"        <terminal value=\"8\"/>"
		"        <terminal value=\"9\"/>"
		"      </alternation>"
		"    </repetition>"
		"  </definition>"
		"</grammar>";


	// parse some input
	stdoutput.write("parsing: 12+34\n\n");

	domnode		*out=new domnode(NULL);
	const char	*codeposition=NULL;

	if (ct.parse("12+34",grammar,"expression",out,&codeposition)) {

		// print the resulting tree
		stdoutput.write("parse tree:\n");
		printtree(out,0);
		stdoutput.write('\n');

		// write the tree back out as code
		stringbuffer	sb;
		ct.write(out,grammar,&sb);
		stdoutput.printf("write output: %s\n",sb.getString());

	} else {
		stdoutput.write("parse failed");
		if (codeposition) {
			stdoutput.printf(" at: %s",codeposition);
		}
		stdoutput.write('\n');
	}

	delete out;
}