refac(depth_first_search): subroutine -> function

Author: Damian Rouson

src/dag_s.f90

@@ -42,7 +42,7 @@ pure module function topological_sort(dag) result(order)
 
       do v = 1, size(dag%vertices)
         if (.not. any(v == searched_and_ordered%s)) then
-          call depth_first_search(v, [integer::], searched_and_ordered%o, searched_and_ordered%s)
+          searched_and_ordered = depth_first_search(v, [integer::], searched_and_ordered%o)
           discovered = [discovered, searched_and_ordered%s]
           searched_and_ordered%s= discovered
         end if
@@ -52,10 +52,10 @@ pure module function topological_sort(dag) result(order)
 
   contains
 
-    pure recursive subroutine depth_first_search(v, d, o, s)
-      integer, intent(in) :: v, d(:)
-      integer, intent(out), allocatable :: s(:)
-      integer, intent(inout), allocatable :: o(:)
+    pure recursive function depth_first_search(v, d, o) result(result_)
+      integer, intent(in) :: v
+      integer, intent(in), dimension(:) :: d, o
+      type(searched_and_ordered_t) result_
 
       call assert(.not. any(v == d), "depth_first_search: cycle detected", intrinsic_array_t([v,d]))
 
@@ -64,25 +64,24 @@ pure recursive subroutine depth_first_search(v, d, o, s)
         integer w
         type(searched_and_ordered_t) hybrid
 
-        hybrid%o = o
+        hybrid = searched_and_ordered_t(s = [integer::], o = o)
         dependencies = dag%depends_on(v)
 
-        allocate(d_local(0), hybrid%s(0))
+        allocate(d_local(0))
 
         do w = 1, size(dependencies)
           if (.not. any(dependencies(w) == hybrid%s)) then
-            call depth_first_search(dependencies(w), [d, v], hybrid%o, hybrid%s)
+            hybrid = depth_first_search(dependencies(w), [d, v], hybrid%o)
             d_local = [d_local, hybrid%s]
             hybrid%s = d_local
           end if
         end do
 
         if (.not. any(v == hybrid%o)) hybrid%o = [v, hybrid%o]
-        s = [v, hybrid%s]
-        o = hybrid%o
+        result_ = searched_and_ordered_t(s = [v, hybrid%s], o = hybrid%o)
       end block
 
-    end subroutine
+    end function
 
   end function topological_sort