document java interpretere

java/lox-interpreter/src/main/java/ch/vanwa/lox_interpreter/Interpreter.java

@@ -1,5 +1,8 @@
 package ch.vanwa.lox_interpreter;
 
+/**
+ * Evaluate Lox expressions.
+ */
 class Interpreter implements Expr.Visitor<Object> {
   void interpret(Expr expression) {
     try {
@@ -87,12 +90,18 @@ class Interpreter implements Expr.Visitor<Object> {
     return null;
   }
 
+  /**
+   * Throw a runtime error if the operand is not an instance of Double.
+   */
   private void checkNumberOperand(Token operator, Object operand) {
     if (operand instanceof Double)
       return;
     throw new RuntimeError(operator, "Operand must be a number.");
   }
 
+  /**
+   * Throw a runtime error if left and right are not both instances of Double.
+   */
   private void checkNumberOperands(Token operator,
       Object left, Object right) {
     if (left instanceof Double && right instanceof Double)
@@ -101,6 +110,9 @@ class Interpreter implements Expr.Visitor<Object> {
     throw new RuntimeError(operator, "Operands must be numbers.");
   }
 
+  /**
+   * Return true if the object is a boolean with value true, false otherwise.
+   */
   private boolean isTruthy(Object object) {
     if (object == null)
       return false;
@@ -109,6 +121,10 @@ class Interpreter implements Expr.Visitor<Object> {
     return true;
   }
 
+  /**
+   * Return true if object a and b are not null and a equals be, otherwise return
+   * false.
+   */
   private boolean isEqual(Object a, Object b) {
     if (a == null && b == null)
       return true;
@@ -118,6 +134,12 @@ class Interpreter implements Expr.Visitor<Object> {
     return a.equals(b);
   }
 
+  /**
+   * Convert an object to a string.
+   *
+   * If the object is null, return "nil", if it is a Double properly print it as a
+   * decimal, otherwise just call toString.
+   */
   private String stringify(Object object) {
     if (object == null) {
       return "nil";