Interpreter.diff

diff --git a/java/com/craftinginterpreters/lox/Interpreter.java b/java/com/craftinginterpreters/lox/Interpreter.java
index 823503f4..1bf3d9a7 100644
--- a/java/com/craftinginterpreters/lox/Interpreter.java
+++ b/java/com/craftinginterpreters/lox/Interpreter.java
@@ -3,6 +3,7 @@ package com.craftinginterpreters.lox;
 //> Statements and State import-list
 
 //> Functions import-array-list
+import java.io.IOException;
 import java.util.ArrayList;
 //< Functions import-array-list
 //> Resolving and Binding import-hash-map
@@ -12,6 +13,8 @@ import java.util.List;
 //< Statements and State import-list
 //> Resolving and Binding import-map
 import java.util.Map;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
 //< Resolving and Binding import-map
 
 /* Evaluating Expressions interpreter-class < Statements and State interpreter
@@ -46,6 +49,82 @@ class Interpreter implements Expr.Visitor<Object>,
         return (double)System.currentTimeMillis() / 1000.0;
       }
 
+      @Override
+      public String toString() { return "<native fn>"; }
+    });
+    globals.define("read", new LoxCallable() {
+      @Override
+      public int arity() { return 0; }
+
+      @Override
+      public Object call(Interpreter interpreter,
+                         List<Object> arguments) {
+        try
+        {
+          int b = System.in.read();
+          return b == -1 ? null : (double)b;
+        } catch (IOException e)
+        {
+          throw new RuntimeException(e);
+        }
+      }
+
+      @Override
+      public String toString() { return "<native fn>"; }
+    });
+    globals.define("utf", new LoxCallable() {
+      @Override
+      public int arity() { return 4; }
+
+      @Override
+      public Object call(Interpreter interpreter,
+                         List<Object> arguments) {
+        Object o1 = arguments.get(0);
+        Object o2 = arguments.get(1);
+        Object o3 = arguments.get(2);
+        Object o4 = arguments.get(3);
+        byte[] bytes = new byte[] {
+                o1 == null ? 0 : ((Double)o1).byteValue(),
+                o2 == null ? 0 : ((Double)o2).byteValue(),
+                o3 == null ? 0 : ((Double)o3).byteValue(),
+                o4 == null ? 0 : ((Double)o4).byteValue()
+        };
+        int count = 0;
+        if (o1 != null) count++;
+        if (o2 != null) count++;
+        if (o3 != null) count++;
+        if (o4 != null) count++;
+        return new String(bytes, 0, count, UTF_8);
+      }
+
+      @Override
+      public String toString() { return "<native fn>"; }
+    });
+    globals.define("exit", new LoxCallable() {
+      @Override
+      public int arity() { return 1; }
+
+      @Override
+      public Object call(Interpreter interpreter,
+                         List<Object> arguments) {
+        System.exit((int)(double)arguments.get(0));
+        return null;
+      }
+
+      @Override
+      public String toString() { return "<native fn>"; }
+    });
+    globals.define("printerr", new LoxCallable() {
+      @Override
+      public int arity() { return 1; }
+
+      @Override
+      public Object call(Interpreter interpreter,
+                         List<Object> arguments) {
+        System.err.println(arguments.get(0));
+        return null;
+      }
+
       @Override
       public String toString() { return "<native fn>"; }
     });