A very naive string node has been added

src/main/java/serene/simple/NumberNode.java

@@ -16,4 +16,4 @@ public class NumberNode extends Node {
   public String toString() {
     return String.format("%s", this.value);
   }
- }
+}

src/main/java/serene/simple/Reader.java

@@ -20,6 +20,9 @@ public class Reader {
     else if (Character.isDigit(c)) {
       return readNumber(inputStream);
     }
+    else if (c == '"') {
+      return readString(inputStream);
+    }
     else if (c == ')') {
       throw new IllegalArgumentException("Unmatch paranthesis.");
     }
@@ -109,6 +112,24 @@ public class Reader {
     return new NumberNode(Long.parseLong(number, 10));
   }
 
+  private static Node readString(PushbackReader inputStream) throws IOException {
+    char opening = (char) inputStream.read();
+    assert opening == '"' : "Strings should start with \"";
+    String str = "";
+
+    while (true) {
+      char ch = (char) inputStream.read();
+
+      if(ch == '"') {
+        break;
+      }
+      str = str + ch;
+    };
+
+    return new StringNode(str);
+
+  }
+
   private static void skipWhiteSpaces(PushbackReader inputStream) throws IOException {
     int ch = inputStream.read();
 

src/main/java/serene/simple/StringNode.java

@@ -0,0 +1,19 @@
+package serene.simple;
+
+public class StringNode extends Node {
+  private final String value;
+
+  public StringNode(String v) {
+    this.value = v;
+  }
+
+  @Override
+  public Object eval(BaseScope scope) {
+    return this.value;
+  }
+
+  @Override
+  public String toString() {
+    return this.value;
+  }
+}