Add --quiet option to supress anything on stdout.

build.gradle

@@ -119,7 +119,7 @@ task preprocessRelationTest(type: JavaExec, group: 'verification') {
     classpath = sourceSets.main.runtimeClasspath
     main = 'org.jastadd.relast.compiler.Compiler'
     //noinspection GroovyAssignabilityCheck
-    args 'src/test/jastadd/relations/Relations.relast', '--useJastAddNames', '--file', '--grammarName=src/test/jastadd/relations/Relations'
+    args 'src/test/jastadd/relations/Relations.relast', '--quiet', '--useJastAddNames', '--file', '--grammarName=src/test/jastadd/relations/Relations'
 }
 
 task doublePreprocessRelationTest(type: JavaExec, group: 'verification') {
@@ -131,7 +131,7 @@ task doublePreprocessRelationTest(type: JavaExec, group: 'verification') {
     classpath = sourceSets.main.runtimeClasspath
     main = 'org.jastadd.relast.compiler.Compiler'
     //noinspection GroovyAssignabilityCheck
-    args 'src/test/jastadd/relations/Relations.ast', '--useJastAddNames', '--file', '--grammarName=src/test/jastadd/relations/Relations2'
+    args 'src/test/jastadd/relations/Relations.ast', '--quiet', '--useJastAddNames', '--file', '--grammarName=src/test/jastadd/relations/Relations2'
 }
 
 task compileRelationTest(type: JavaExec, group: 'verification') {

buildSrc/src/main/java/org/jastadd/relast/plugin/RelastTest.java

@@ -193,6 +193,7 @@ public class RelastTest extends DefaultTask {
         javaExecSpec.setClasspath(runtimeClasspath);
         javaExecSpec.setMain("org.jastadd.relast.compiler.Compiler");
         List<Object> args = new ArrayList<>(getRelastFiles());
+        args.add("--quiet");
         if (isWriteToFile()) {
           args.add("--file");
         }

src/main/java/org/jastadd/relast/compiler/Compiler.java

@@ -25,16 +25,18 @@ public class Compiler {
   private EnumOption optionSerializer;
   private FlagOption optionResolverHelper;
   private FlagOption optionUseJastaddNames;
+  private FlagOption optionQuiet;
   private CommandLine commandLine;
 
   public Compiler(String[] args) throws CommandLineException {
-    System.out.println("Running RelAST " + VERSION);
     options = new ArrayList<>();
     addOptions();
 
     commandLine = new CommandLine(options);
     commandLine.parse(args);
 
+    printMessage("Running RelAST " + VERSION);
+
     if (commandLine.getArguments().size() < 1) {
       error("specify at least one input file");
     }
@@ -43,7 +45,7 @@ public class Compiler {
     Program p = parseProgram(filenames);
 
     if (optionJastAddList.isSet()) {
-      System.out.println("JastAdd List type is set to " + optionJastAddList.getValue());
+      printMessage("JastAdd List type is set to " + optionJastAddList.getValue());
       ASTNode.jastAddListType = optionJastAddList.getValue();
     }
 
@@ -68,7 +70,7 @@ public class Compiler {
     } else {
 
       if (optionListClass.isSet()) {
-        System.out.println("ListClass is set to " + optionListClass.getValue());
+        printMessage("ListClass is set to " + optionListClass.getValue());
         ASTNode.listClass = optionListClass.getValue();
       }
 
@@ -109,8 +111,8 @@ public class Compiler {
       } else if (optionPrintAST.isSet()) {
         System.out.println(p.dumpTree());
       } else {
-        System.out.println(p.generateAbstractGrammar());
-        System.out.println(p.generateAspect());
+        printMessage(p.generateAbstractGrammar());
+        printMessage(p.generateAspect());
       }
     }
   }
@@ -119,11 +121,17 @@ public class Compiler {
     try {
       new Compiler(args);
     } catch (CommandLineException e) {
-      System.out.println(e.getMessage());
+      System.err.println(e.getMessage());
       System.exit(1);
     }
   }
 
+  private void printMessage(String message) {
+    if (!optionQuiet.isSet()) {
+      System.out.println(message);
+    }
+  }
+
   private void writeToFile(String filename, String str) {
     try {
       PrintWriter writer = new PrintWriter(filename);
@@ -137,14 +145,14 @@ public class Compiler {
 
   private void addOptions() {
     optionWriteToFile = addOption(new FlagOption("file", "write output to files <filename>Gen.ast and <filename>Gen.jadd"));
-    optionPrintAST = addOption(new FlagOption("ast", "print AST"));
+    optionPrintAST = addOption(new FlagOption("ast", "print AST (ignores quiet option)"));
     optionListClass = addOption(new StringOption("listClass", "determine the class name of the nonterminal reference list"));
     optionGrammarName = addOption(new StringOption("grammarName", "name of the generated grammar and aspect (without file extension)"));
     optionResolverHelper = addOption(new FlagOption("resolverHelper", "create a subtype for each type containing a string that can be used to resolve the type later"));
     optionJastAddList = addOption(new StringOption("jastAddList", "set the name of the List type in JastAdd (has to match the option '--List' or its default List)"));
     optionUseJastaddNames = addOption(new FlagOption("useJastAddNames", "generate names in the form of addX, removeX and setX. If omitted, the default, original naming scheme resulting in addToX, removeFromX and setX will be used."));
     optionSerializer = addOption(new EnumOption("serializer", "generate a (de-)serializer", Arrays.asList("jackson"), "jackson"));
-
+    optionQuiet = addOption(new FlagOption("quiet", "do not output anything on stdout"));
   }
 
   private <OptionType extends Option<?>> OptionType addOption(OptionType option) {