Index: src/natools-s_expressions-file_writers.adb
==================================================================
--- src/natools-s_expressions-file_writers.adb
+++ src/natools-s_expressions-file_writers.adb
@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
--- Copyright (c) 2014, Natacha Porté                                        --
+-- Copyright (c) 2014-2017, Natacha Porté                                   --
 --                                                                          --
 -- Permission to use, copy, modify, and distribute this software for any    --
 -- purpose with or without fee is hereby granted, provided that the above   --
 -- copyright notice and this permission notice appear in all copies.        --
 --                                                                          --
@@ -72,12 +72,40 @@
    begin
       Finalize (Self.Holder);
       Stream_IO.Open (Self.Holder.File, Stream_IO.Append_File, Name, Form);
    end Open;
 
+
+   function Open_Or_Create (Name : String; Form : String := "")
+     return Writer is
+   begin
+      return Result : Writer do
+         Open_Or_Create (Result, Name, Form);
+      end return;
+   end Open_Or_Create;
+
+
+   procedure Open_Or_Create
+     (Self : in out Writer;
+      Name : in String;
+      Form : in String := "") is
+   begin
+      Finalize (Self.Holder);
+
+      Open_Attempt :
+      begin
+         Stream_IO.Open (Self.Holder.File, Stream_IO.Append_File, Name, Form);
+         return;
+      exception
+         when Stream_IO.Name_Error => null;
+      end Open_Attempt;
+
+      Stream_IO.Create (Self.Holder.File, Stream_IO.Append_File, Name, Form);
+   end Open_Or_Create;
+
 
    function Name (Self : Writer) return String is
    begin
       return Stream_IO.Name (Self.Holder.File);
    end Name;
 
 end Natools.S_Expressions.File_Writers;

Index: src/natools-s_expressions-file_writers.ads
==================================================================
--- src/natools-s_expressions-file_writers.ads
+++ src/natools-s_expressions-file_writers.ads
@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
--- Copyright (c) 2014, Natacha Porté                                        --
+-- Copyright (c) 2014-2017, Natacha Porté                                   --
 --                                                                          --
 -- Permission to use, copy, modify, and distribute this software for any    --
 -- purpose with or without fee is hereby granted, provided that the above   --
 -- copyright notice and this permission notice appear in all copies.        --
 --                                                                          --
@@ -39,10 +39,20 @@
    procedure Open
      (Self : in out Writer;
       Name : in String;
       Form : in String := "");
       --  Reinitialize Self using Stream_IO.Create or Stream_IO.Open
+
+   function Open_Or_Create (Name : String; Form : String := "") return Writer;
+   procedure Open_Or_Create
+     (Self : in out Writer;
+      Name : in String;
+      Form : in String := "");
+      --  Construct or reinitialize a writer, trying a regular open first
+      --  and attempting to create if it doesn't work.
+      --  Note that there is some time between failure to open and actual
+      --  file creation, which might lead to race conditions.
 
    function Name (Self : Writer) return String;
       --  Return the underlying file name
 
 private