1 files changed, 41 insertions, 0 deletions
diff --git a/vm_eval.c b/vm_eval.c
index 8e6bd76e9e..e9774d2785 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -1377,11 +1377,52 @@ rb_f_local_variables(void)
     return ary;
 }
 
+/*
+ *  call-seq:
+ *     block_given?   => true or false
+ *     iterator?      => true or false
+ *
+ *  Returns <code>true</code> if <code>yield</code> would execute a
+ *  block in the current context. The <code>iterator?</code> form
+ *  is mildly deprecated.
+ *
+ *     def try
+ *       if block_given?
+ *         yield
+ *       else
+ *         "no block"
+ *       end
+ *     end
+ *     try                  #=> "no block"
+ *     try { "hello" }      #=> "hello"
+ *     try do "hello" end   #=> "hello"
+ */
+
+
+VALUE
+rb_f_block_given_p(void)
+{
+    rb_thread_t *th = GET_THREAD();
+    rb_control_frame_t *cfp = th->cfp;
+    cfp = vm_get_ruby_level_caller_cfp(th, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));
+
+    if (cfp != 0 &&
+	(cfp->lfp[0] & 0x02) == 0 &&
+	GC_GUARDED_PTR_REF(cfp->lfp[0])) {
+	return Qtrue;
+    }
+    else {
+	return Qfalse;
+    }
+}
+
 void
 Init_vm_eval(void)
 {
     rb_define_global_function("eval", rb_f_eval, -1);
     rb_define_global_function("local_variables", rb_f_local_variables, 0);
+    rb_define_global_function("iterator?", rb_f_block_given_p, 0);
+    rb_define_global_function("block_given?", rb_f_block_given_p, 0);
 
     rb_define_global_function("catch", rb_f_catch, -1);
     rb_define_global_function("throw", rb_f_throw, -1);