Add conditionnal grammar file for #2

java-vtl-parser/src/main/antlr4/imports/Relational.g4

@@ -0,0 +1,10 @@
+grammar Relational;
+
+relationalExpression : unionExpression ;
+
+unionExpression : 'union' '(' datasetExpression (',' datasetExpression)+ ')' ;
+
+datasetExpression : 'datasetExpr' NUM+;
+
+
+NUM : '0'..'9' ;

java-vtl-parser/src/test/java/imports/UnionParserTest.java

@@ -0,0 +1,57 @@
+package imports;
+
+
+import com.google.common.io.Resources;
+import org.antlr.v4.runtime.ANTLRInputStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.LexerInterpreter;
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.antlr.v4.tool.Grammar;
+import org.antlr.v4.tool.GrammarParserInterpreter;
+import org.antlr.v4.tool.Rule;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.rules.ExternalResource;
+
+import java.net.URL;
+import java.nio.charset.Charset;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.io.Resources.getResource;
+
+public class UnionParserTest {
+
+    private static Grammar grammar;
+    @ClassRule
+    public static ExternalResource grammarResource = new ExternalResource() {
+        @Override
+        protected void before() throws Throwable {
+            URL grammarURL = getResource(this.getClass(), "Relational.g4");
+            String grammarString = Resources.toString(grammarURL, Charset.defaultCharset());
+            grammar = new Grammar(checkNotNull(grammarString));
+        }
+    };
+
+
+    @Test
+    public void testUnion() throws Exception {
+        String expression = "union ( dataset1, dataset2, dataset3)";
+
+
+    }
+
+    // TODO: Build a more robust way to test.
+    private String parse(String expression) {
+        LexerInterpreter lexerInterpreter = grammar.createLexerInterpreter(
+                new ANTLRInputStream(expression)
+        );
+        GrammarParserInterpreter parserInterpreter = grammar.createGrammarParserInterpreter(
+                new CommonTokenStream(lexerInterpreter)
+        );
+
+        Rule clause = grammar.getRule("clauseExpression");
+        parserInterpreter.setErrorHandler(new GrammarParserInterpreter.BailButConsumeErrorStrategy());
+        ParserRuleContext parse = parserInterpreter.parse(clause.index);
+        return parse.toStringTree(parserInterpreter);
+    }
+}