     return
   }
 
-  func parseSources(yaml: Yaml) {
+  func parseSources(yaml: Yaml) -> ParsingError? {
     if let sourcesYamls = yaml.array {
       sources = sourcesYamls.map { (s) in
         return s.string!
       }
-    } else {
-      print("Cannot parse sources")
+      return nil
+    } else {
+      return ParsingError(message: "Cannot parse sources")
     }
   }
 

      "compiler_options":       self.parseCompilerOptions,
      "dependencies":           self.parseDependencies,
      "linker_options":         self.parseLinkerOptions,
      "test_target":            self.parseTestTarget,
    ]


    let unfailableActionMap = [
      "name":                   self.parseName,
      "version":                self.parseVersion,
      "modules":                self.parseModules,
      "framework_search_paths": self.parseFrameworkSearchPaths,
      "target_type":            self.parseTargetType,
