Invalid code in class_assign_1.f08

[Neil Carlson]

The code class_assign_1.f08 makes inappropriate use of the MODULE attribute in several places (there are no submodules involved here). In addition, the abstract interface for base_add needs to import the derived type base; the interface body is a separate scoping unit and doesn't know anything about base otherwise (this suggests gfortran has a bug here).

With this diff the code compiles and runs cleanly with NAG 6.1 and Intel 18.0.1

diff --git a/class_assign_1.f08 b/class_assign_1.f08
index fb1f655..3d4cc48 100644
--- a/class_assign_1.f08
+++ b/class_assign_1.f08
@@ -12,7 +12,8 @@ module base_mod
   end type base
 
   abstract interface
-    module function base_add(l, r) result(res)
+    function base_add(l, r) result(res)
+      import base
       class(base), intent(in) :: l
       integer, intent(in) :: r
       class(base), allocatable :: res
@@ -41,7 +42,7 @@ module extend_mod
   end type extend
 
 contains
-  module function add(l, r) result(res)
+  function add(l, r) result(res)
     class(extend), intent(in) :: l
     integer, intent(in) :: r
     class(base), allocatable :: res