Variable_Primary returns PrimaryVariable:
	name=Variable_Name
	
;

Variable_Name: 
	ID | 'E' | 'e'
;

Real_Value returns ecore::EDouble:
	Signed_Int '.' UNSIGNED_INT ('E' Signed_Int)?
;

terminal UNSIGNED_INT returns ecore::ELong:
	DIGIT ('_'? DIGIT)*
;

terminal fragment LETTER: 'a'..'z' | 'A'..'Z' | '_';
terminal fragment DIGIT: '0'..'9';

terminal ID:
 	DIGIT? LETTER (LETTER | DIGIT)* 	
;

@Check
def checkVariableName(Variable_Primary toCheck) {
  if (toCheck.hasParentheses) {
      error('The name cannot has parentheses.', toCheck, ...)
  }
}

@Test def testParseIllegalVarName(){
		parseFunctionBlock('''
			FUNCTION_BLOCK 3V0
			 VAR_INPUT
			  e:BOOL;
			  E:BOOL;
			  X:NUMERIC:=1.23E-23;
			 END_VAR
			 VAR_OUTPUT
			  B:BOOL;
			  D:BOOL;
			 END_VAR
			 VAR
			  C(1):BOOL;
			 END_VAR
			END_FUNCTION_BLOCK
		''').assertNoErrors
	}

package org.xtext.example.mydsl;

import org.eclipse.xtext.common.services.DefaultTerminalConverters;
import org.eclipse.xtext.conversion.IValueConverter;
import org.eclipse.xtext.conversion.ValueConverter;
import org.eclipse.xtext.conversion.ValueConverterException;
import org.eclipse.xtext.conversion.impl.KeywordAlternativeConverter;
import org.eclipse.xtext.nodemodel.INode;

import com.google.inject.Inject;

public class MyDslValueConverterService extends DefaultTerminalConverters {
	
	@Inject
	private VarNameVC varNameVC;

	@ValueConverter(rule = "Variable_Name")
	public IValueConverter<String> Variable_Name() {
		return varNameVC;
	}
	
	public static class VarNameVC implements IValueConverter<String> {

		@Override
		public String toValue(String string, INode node) throws ValueConverterException {
			return string;
		}

		@Override
		public String toString(String value) throws ValueConverterException {
			if (value.contains("(")) {
				throw new ValueConverterException("mimimi", null, null);
			}
			return value;
		}
		
	}

}

public static class MyDslParser2 extends MyDslParser {
		public IParseResult doParseVarName(CharSequence sequence) {
			try {
				return parse("Variable_Name", new ANTLRReaderStream(new StringReader(sequence.toString())));
			} catch (IOException e) {
				throw new WrappedException(e);
			}
		}
	}
	
	public static class VarNameVC implements IValueConverter<String> {
		
		@Inject
		MyDslParser2 p;


		@Override
		public String toValue(String string, INode node) throws ValueConverterException {
			return string;
		}

		@Override
		public String toString(String value) throws ValueConverterException {
			IParseResult result = p.doParseVarName(value);
			if (result.hasSyntaxErrors()) {
				System.err.println(result.getSyntaxErrors());
				throw new ValueConverterException("mimimi", null, null);
			}
			return value;
		}