An Xtext workflow written as an Xtend class.

GenerateMyDsl.xtend

package org.xtext.example.mydsl

import org.eclipse.emf.mwe.utils.DirectoryCleaner
import org.eclipse.emf.mwe.utils.StandaloneSetup
import org.eclipse.xtext.generator.Generator
import org.eclipse.xtext.generator.LanguageConfig
import org.eclipse.xtext.generator.builder.BuilderIntegrationFragment
import org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment
import org.eclipse.xtext.generator.exporting.QualifiedNamesFragment
import org.eclipse.xtext.generator.formatting.FormatterFragment
import org.eclipse.xtext.generator.generator.GeneratorFragment
import org.eclipse.xtext.generator.grammarAccess.GrammarAccessFragment
import org.eclipse.xtext.generator.junit.Junit4Fragment
import org.eclipse.xtext.generator.parser.antlr.XtextAntlrGeneratorFragment
import org.eclipse.xtext.generator.parser.antlr.XtextAntlrUiGeneratorFragment
import org.eclipse.xtext.generator.resourceFactory.ResourceFactoryFragment
import org.eclipse.xtext.generator.scoping.ImportNamespacesScopingFragment
import org.eclipse.xtext.generator.serializer.SerializerFragment
import org.eclipse.xtext.generator.types.TypesGeneratorFragment
import org.eclipse.xtext.generator.validation.ValidatorFragment
import org.eclipse.xtext.generator.xbase.XbaseGeneratorFragment
import org.eclipse.xtext.ui.generator.compare.CompareFragment
import org.eclipse.xtext.ui.generator.contentAssist.ContentAssistFragment
import org.eclipse.xtext.ui.generator.labeling.LabelProviderFragment
import org.eclipse.xtext.ui.generator.outline.OutlineTreeProviderFragment
import org.eclipse.xtext.ui.generator.outline.QuickOutlineFragment
import org.eclipse.xtext.ui.generator.quickfix.QuickfixProviderFragment
import org.eclipse.xtext.ui.generator.refactoring.RefactorElementNameFragment
import org.eclipse.xtext.ui.generator.templates.CodetemplatesGeneratorFragment

class GenerateMyDsl extends XtendWorkflow {

  String grammarURI = "classpath:/org/xtext/example/mydsl/MyDsl.xtext"
	String fileExtensions = "mydsl"
	String projectName = "org.xtext.example.mydsl"
	String runtimeProject = "../${projectName}".resolve
	boolean generateXtendStub = true

	new() {
		beans += new StandaloneSetup => [
			scanClassPath = true
			platformUri = "${runtimeProject}/..".resolve
			// The following two lines can be removed, if Xbase is not used.
			addRegisterGeneratedEPackage("org.eclipse.xtext.xbase.XbasePackage")
			addRegisterGenModelFile("platform:/resource/org.eclipse.xtext.xbase/model/Xbase.genmodel")
		]

		components += new DirectoryCleaner => [
			directory = "${runtimeProject}/src-gen".resolve
		]

		components += new DirectoryCleaner => [
			directory = "${runtimeProject}.ui/src-gen".resolve
		]

		components += new Generator => [
			pathRtProject = runtimeProject
			pathUiProject = "${runtimeProject}.ui".resolve
			pathTestProject = "${runtimeProject}.tests".resolve
			projectNameRt = projectName
			projectNameUi = "${projectName}.ui".resolve
			addLanguage(
				new LanguageConfig => [
					autoInject
					uri = grammarURI
					// Java API to access grammar elements (required by several other fragments)
					addFragment(new GrammarAccessFragment => [autoInject])
					// generates Java API for the generated EPackages
					addFragment(
						new EcoreGeneratorFragment => [
							autoInject
						// referencedGenModels = "
						//  platform:/resource/org.eclipse.xtext.xbase/model/Xbase.genmodel,
						//  platform:/resource/org.eclipse.xtext.common.types/model/JavaVMTypes.genmodel
						// "
						])
					// the old serialization component
					// fragment = parseTreeConstructor.ParseTreeConstructorFragment auto-inject {}    
					// serializer 2.0
					addFragment(
						new SerializerFragment => [
							autoInject
							generateStub = false
						])
					// a custom ResourceFactory for use with EMF
					addFragment(
						new ResourceFactoryFragment => [
							autoInject
						])
					// The antlr parser generator fragment.
					addFragment(
						new XtextAntlrGeneratorFragment => [
							autoInject
						//  options = {
						//      backtrack = true
						//  }
						])
					// Xtend-based API for validation
					addFragment(
						new ValidatorFragment => [
							autoInject
						//    composedCheck = "org.eclipse.xtext.validation.ImportUriValidator"
						//    composedCheck = "org.eclipse.xtext.validation.NamesAreUniqueValidator"
						])
					// old scoping and exporting API
					// fragment = scoping.ImportURIScopingFragment auto-inject {}
					// fragment = exporting.SimpleNamesFragment auto-inject {}
					// scoping and exporting API
					addFragment(
						new ImportNamespacesScopingFragment => [
							autoInject
						])
					addFragment(
						new QualifiedNamesFragment => [
							autoInject
						])
					addFragment(
						new BuilderIntegrationFragment => [
							autoInject
						])
					// generator API
					addFragment(
						new GeneratorFragment => [
							autoInject
						])
					// formatter API
					addFragment(
						new FormatterFragment => [
							autoInject
						])
					// labeling API
					addFragment(
						new LabelProviderFragment => [
							autoInject
						])
					// outline API
					addFragment(
						new OutlineTreeProviderFragment => [
							autoInject
						])
					addFragment(
						new QuickOutlineFragment => [
							autoInject
						])
					// quickfix API
					addFragment(
						new QuickfixProviderFragment => [
							autoInject
						])
					// content assist API
					addFragment(
						new ContentAssistFragment => [
							autoInject
						])
					// generates a more lightweight Antlr parser and lexer tailored for content assist
					addFragment(
						new XtextAntlrUiGeneratorFragment => [
							autoInject
						])
					// generates junit test support classes into Generator#pathTestProject
					addFragment(
						new Junit4Fragment => [
							autoInject
						])
					// project wizard (optional)
					// fragment = projectWizard.SimpleProjectWizardFragment auto-inject {
					//      generatorProjectName = "${projectName}"
					// }
					// rename refactoring
					addFragment(
						new RefactorElementNameFragment => [
							autoInject
						])
					// provides the necessary bindings for java types integration
					addFragment(
						new TypesGeneratorFragment => [
							autoInject
						])
					// generates the required bindings only if the grammar inherits from Xbase
					addFragment(
						new XbaseGeneratorFragment => [
							autoInject
						])
					// provides a preference page for template proposals
					addFragment(
						new CodetemplatesGeneratorFragment => [
							autoInject
						])
					// provides a compare view
					addFragment(
						new CompareFragment => [
							autoInject
						])
				])
		]
	}

	def static void main(String[] args) {
		new GenerateMyDsl().run(null)
	}

}

XtendWorkflow.java

package org.xtext.example.mydsl;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.eclipse.emf.mwe2.runtime.workflow.IWorkflowComponent;
import org.eclipse.emf.mwe2.runtime.workflow.Workflow;
import org.eclipse.xtext.util.Strings;

import com.google.common.collect.Lists;

public class XtendWorkflow extends Workflow {

  protected List<Object> getBeans() {
		return Lists.newArrayList();
	}

	protected List<IWorkflowComponent> getComponents() {
		return getChildren();
	}

	protected <T> T autoInject(T t) {
		Class<?> tClass = t.getClass();
		for (Field field : getClass().getFields()) {
			String name = field.getName();
			Class<?> type = field.getType();
			try {
				Method setter = tClass.getMethod(
						"set" + Strings.toFirstUpper(name), type);
				field.setAccessible(true);
				setter.setAccessible(true);
				setter.invoke(t, field.get(this));
			} catch (SecurityException e) {
				e.printStackTrace();
			} catch (NoSuchMethodException e) {
				// no problem
			} catch (IllegalArgumentException e) {
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				e.printStackTrace();
			} catch (InvocationTargetException e) {
				e.printStackTrace();
			}
		}
		return t;
	}

	private static final Pattern VAR_PATTERN = Pattern.compile("\\$\\{([^\\}]+)\\}");

	protected String resolve(String s) {
		Matcher matcher = VAR_PATTERN.matcher(s);
		StringBuilder result = new StringBuilder();
		int last = 0;
		while (matcher.find()) {
			result.append(s.substring(last, matcher.start()));
			String group = matcher.group(1);
			result.append(getFieldValue(group));
			last = matcher.end();
		}
		result.append(s.substring(last));
		return result.toString();
	}

	private Object getFieldValue(String fieldName) {
		try {
			Field field = getClass().getDeclaredField(fieldName);
			field.setAccessible(true);
			return field.get(this);
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			e.printStackTrace();
		}
		return null;
	}
}

Somehow I managed to create this Gist in anonymous mode, so I've created a fork for the updated example: https://gist.github.com/4676978.