Implem of Build.progn

src/build.ml

@@ -190,3 +190,32 @@ let and_create_file fn =
     { action with
       action = Progn [action.action; Create_file fn]
     })
+
+(*
+   {[
+     let progn ts =
+       all ts >>^ fun (actions : Action.t list) ->
+       match actions with
+       | [] ->
+         { Action.
+           context = None
+         ; dir     = Path.root
+         ; action  = Progn []
+         }
+       | first :: rest ->
+         let rest =
+           List.map rest ~f:(fun a ->
+             (match first.context, a.context with
+              | None, None -> ()
+              | Some c1, Some c2 when c1.name = c2.name -> ()
+              | _ ->
+                Sexp.code_error "Build.progn"
+                  [ "actions", Sexp.To_sexp.list Action.sexp_of_t actions ]);
+             if first.dir = a.dir then
+               a.action
+             else
+               Chdir (a.dir, a.action))
+         in
+         { first with action = Progn (first :: rest) }
+   ]}
+*)