diff --git a/src/som/primitives/StringPrimitives.java b/src/som/primitives/StringPrimitives.java
index a5e34fe..f05af02 100644
--- a/src/som/primitives/StringPrimitives.java
+++ b/src/som/primitives/StringPrimitives.java
@@ -118,5 +118,43 @@ public void invoke(final Frame frame, final Interpreter interpreter) {
       }
     });
 
+    installInstancePrimitive(new SPrimitive("isWhiteSpace", universe) {
+
+      @Override
+      public void invoke(final Frame frame, final Interpreter interpreter) {
+        SString self = (SString) frame.pop();
+        if (Character.isWhitespace(self.getEmbeddedString().charAt(0))) {
+          frame.push(universe.trueObject);
+        } else {
+          frame.push(universe.falseObject);
+        }
+      }
+    });
+
+    installInstancePrimitive(new SPrimitive("isLetter", universe) {
+
+      @Override
+      public void invoke(final Frame frame, final Interpreter interpreter) {
+        SString self = (SString) frame.pop();
+        if (Character.isLetter(self.getEmbeddedString().charAt(0))) {
+          frame.push(universe.trueObject);
+        } else {
+          frame.push(universe.falseObject);
+        }
+      }
+    });
+
+    installInstancePrimitive(new SPrimitive("isDigit", universe) {
+
+      @Override
+      public void invoke(final Frame frame, final Interpreter interpreter) {
+        SString self = (SString) frame.pop();
+        if (Character.isDigit(self.getEmbeddedString().charAt(0))) {
+          frame.push(universe.trueObject);
+        } else {
+          frame.push(universe.falseObject);
+        }
+      }
+    });
   }
 }