I was able to reproduce the crash and got this trace: ******************************** Thread exception ***************************** In thread Root thread 0x0 (thread id) ******************************************************************************* ------------------------------------------------------------------------------- Class / Object Routine Nature of exception Effect ------------------------------------------------------------------------------- CONSTRAINT_LIST_AS reverse_extend_separator @4 <0000000006CC2144> (From EIFFEL_LIST) Feature call on void target. Fail ------------------------------------------------------------------------------- CONSTRAINT_LIST_AS reverse_extend_separator @4 <0000000006CC2144> (From EIFFEL_LIST) Routine failure. Fail ------------------------------------------------------------------------------- AST_ROUNDTRIP_COMPILER_LIGHT_FACTORY reverse_extend_separator @2 <0000000006A03034> (From AST_ROUNDTRIP_LIGHT_FACTORY) Routine failure. Fail ------------------------------------------------------------------------------- EIFFEL_PARSER yy_do_action_288 @4 <0000000008FF2D48> Routine failure. Fail ------------------------------------------------------------------------------- EIFFEL_PARSER yy_do_action_201_400 @89 <0000000008FF2D48> Routine failure. Fail ------------------------------------------------------------------------------- EIFFEL_PARSER yy_do_action @4 <0000000008FF2D48> Routine failure. Fail ------------------------------------------------------------------------------- EIFFEL_PARSER parse @73 <0000000008FF2D48> (From YY_PARSER_SKELETON) Routine failure. Rescue ------------------------------------------------------------------------------- EIFFEL_PARSER parse_class @15 <0000000008FF2D48> (From EIFFEL_PARSER_SKELETON) Routine failure. Rescue ------------------------------------------------------------------------------- EIFFEL_CLASS_C build_ast @21 <0000000006981F14> Routine failure. Rescue ------------------------------------------------------------------------------- DEGREE_5 process_class @6 <0000000006A02968> Routine failure. Fail ------------------------------------------------------------------------------- DEGREE_5 execute @17 <0000000006A02968> Routine failure. Fail ------------------------------------------------------------------------------- SYSTEM_I process_degree_5 @15 <0000000008FACA7C> Routine failure. Fail ------------------------------------------------------------------------------- SYSTEM_I do_recompilation @19 <0000000008FACA7C> Routine failure. Fail ------------------------------------------------------------------------------- SYSTEM_I recompile @6 <0000000008FACA7C> Routine failure. Rescue ------------------------------------------------------------------------------- WORKBENCH_I recompile @23 <00000000078287E8> Routine failure. Rescue ------------------------------------------------------------------------------- E_PROJECT melt @7 <00000000077A0FF0> Routine failure. Rescue ------------------------------------------------------------------------------- E_PROJECT quick_melt @3 <00000000077A0FF0> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND perform_compilation @1 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND compile @5 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND compile_and_run @1 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND confirm_execution_halt @2 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND confirm_and_compile @1 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND compile_no_save @4 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND execute_with_c_compilation_flag @16 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND go_on_compile @1 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EB_MELT_PROJECT_COMMAND execute @11 <000000000783D704> Routine failure. Fail ------------------------------------------------------------------------------- EV_NOTIFY_ACTION_SEQUENCE call @21 <00000000076A5860> (From ACTION_SEQUENCE) Routine failure. Fail ------------------------------------------------------------------------------- EV_NOTIFY_ACTION_SEQUENCE call @3 <00000000076A5860> (From EV_LITE_ACTION_SEQUENCE) Routine failure. Fail ------------------------------------------------------------------------------- EV_APPLICATION_IMP process_event_queue @15 <00000000076A5650> (From EV_APPLICATION_I) Routine failure. Fail ------------------------------------------------------------------------------- EV_APPLICATION_IMP launch @3 <00000000076A5650> (From EV_APPLICATION_I) Routine failure. Fail ------------------------------------------------------------------------------- EV_APPLICATION launch @2 <00000000076A562C> Routine failure. Fail ------------------------------------------------------------------------------- ES_GRAPHIC make @4 <00000000076A5614> Routine failure. Fail ------------------------------------------------------------------------------- EB_KERNEL make @6 <00000000076A55E4> Routine failure. Fail ------------------------------------------------------------------------------- EB_KERNEL root's creation <00000000076A55E4> Routine failure. Exit -------------------------------------------------------------------------------