#11 Custom Terminals

Aug 29, 2012 | 7 minutes | Grammar

Lern how to use custom terminals with value converters to improve your DSL-grammar, model, generator and other Xtext components.

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The Xtext grammar syntax (scroll down for custom terminals): http://www.eclipse.org/Xtext/documentation.html#syntax

Common terminals: http://www.eclipse.org/Xtext/documentation.html#_15

Definition of the custom terminal within the DSL-grammar:

              xtext
                    
        terminal BINARY returns ecore::EInt:
	('0' | '1')+ 'b'
;
        
terminal BINARY returns ecore::EInt:
        ('0' | '1')+ 'b'
;

Declaration of the user defined IValueConverterService:

              MyDslRuntimeModule.java
                    
        public class MyDslRuntimeModule extends org.xtext.example.mydsl.AbstractMyDslRuntimeModule {
	@Override
	public Class<? extends IValueConverterService> bindIValueConverterService() {
		return MyTerminalConverters.class;
	}
}
        
public class MyDslRuntimeModule extends org.xtext.example.mydsl.AbstractMyDslRuntimeModule {
        @Override
        public Class<? extends IValueConverterService> bindIValueConverterService() {
                return MyTerminalConverters.class;
        }
}

Implementation of the user defined IValueConverterService:

              MyTerminalConverters.java
                    
        public class MyTerminalConverters extends DefaultTerminalConverters {
	@Inject
	private BINARYValueConverter binaryValueConverter;
	
	@ValueConverter(rule = "BINARY")
	public IValueConverter<Integer> BINARY() {
		return binaryValueConverter;
	}

}
        
public class MyTerminalConverters extends DefaultTerminalConverters {
        @Inject
        private BINARYValueConverter binaryValueConverter;
        
        @ValueConverter(rule = "BINARY")
        public IValueConverter<Integer> BINARY() {
                return binaryValueConverter;
        }

}

Implementation of the binary number <-> integer converter:

              BINARYValueConverter.java
                    
        public class BINARYValueConverter extends AbstractLexerBasedConverter<Integer> {
	@Override
	protected String toEscapedString(Integer value) {
		return Integer.toBinaryString(value) + "b";
	}
	
	@Override
	protected void assertValidValue(Integer value) {
		super.assertValidValue(value);
		if (value < 0)
			throw new ValueConverterException(getRuleName() + "-value may not be negative (value: " + value + ").", null, null);
	}
	
	public Integer toValue(String string, INode node) {
		if (Strings.isEmpty(string))
			throw new ValueConverterException("Couldn't convert empty string to an binary value.", node, null);
		try {
			int intValue = Integer.parseInt(string.substring(0, string.length() - 1), 2);
			return Integer.valueOf(intValue);
		} catch (NumberFormatException e) {
			throw new ValueConverterException("Couldn't convert '" + string + "' to an binary value.", node, e);
		}
	}

}
        
        
        
        
        
        
        
        
        
      
public class BINARYValueConverter extends AbstractLexerBasedConverter<Integer> {
        @Override
        protected String toEscapedString(Integer value) {
                return Integer.toBinaryString(value) + "b";
        }
        
        @Override
        protected void assertValidValue(Integer value) {
                super.assertValidValue(value);
                if (value < 0)
                        throw new ValueConverterException(getRuleName() + "-value may not be negative (value: " + value + ").", null, null);
        }
        
        public Integer toValue(String string, INode node) {
                if (Strings.isEmpty(string))
                        throw new ValueConverterException("Couldn't convert empty string to an binary value.", node, null);
                try {
                        int intValue = Integer.parseInt(string.substring(0, string.length() - 1), 2);
                        return Integer.valueOf(intValue);
                } catch (NumberFormatException e) {
                        throw new ValueConverterException("Couldn't convert '" + string + "' to an binary value.", node, e);
                }
        }

}