build.xml

<target name="compile" depends="compile-grammar">
    <javac srcdir="${src}" destdir="${build}">
        <classpath refid="classpath.base"/>
    </javac>
</target>

<target name="compile-grammar" depends="-check_grammar_needs_compile"
        if="grammarBuildRequired">
    <java classname="org.antlr.Tool" failonerror="true">
        <arg value="${grammar-file}"/>
        <classpath refid="classpath.antlr"/>
    </java>
</target>

<target name="-check_grammar_needs_compile">
    <uptodate property="grammarBuildRequired" targetfile="${grammar-file}"
        srcfile="${grammar-java-file}"/>
</target>