挺大的改动。增加 as运算符，转换不了抛出 TypeError。import语法更新。修复try一点错误。现在表达式运算返回ExprResult。通过3个宏实现简便错误传播与解包 unwrap

src/Module/Library/lang/lang.fig

@@ -31,6 +31,27 @@ public interface Error
     getErrorMessage() -> String;
 }
 
+public struct TypeError
+{
+    public msg: String;
+}
+
+impl Error for TypeError
+{
+    toString()
+    {
+        return "TypeError: " + getErrorMessage();
+    }
+    getErrorClass()
+    {
+        return "TypeError";
+    }
+    getErrorMessage()
+    {
+        return msg;
+    }
+}
+
 // Operation interface
 
 public interface Operation

src/Module/Library/std/std.fig

@@ -3,7 +3,12 @@
     Library/std/std.fig
 */
 
-import io;    // link std.io
-import value; // link std.type
-import math;  // link std.math
-import tester; // link std.tester
+import io as std_io;
+import value as std_value;
+import math as std_math; 
+import test as std_test; 
+
+public const io := std_io;        // link std.io
+public const value := std_value;  // link std.type
+public const math := std_math;    // link std.math
+public const test := std_test;    // link std.test