New subject: [polyml] exception SysErr

10 Oct 2009


      David,
The basis library documentation for exception SysErr states:
...but if a SysErr exception has the form SysErr (s, SOME e),
  then we have errorMsg e = s.
http://www.standardml.org/Basis/os.html
However, it appears that Poly/ML is not always preserving that property 
because errorMsg e and s are sometimes different strings, for example:
val () = ignore (TextIO.openIn "a non-existent file name")
  handle
    e as IO.Io {cause, ...} => (
      case cause of
        OS.SysErr (s, SOME e) => (
          print "\n";
          app print ["s          = "", s,             ""\n"];
          app print ["errorMsg e = "", OS.errorMsg e, ""\n"]
        )
      | _                     => ()
    );
If the Standard is to be followed and one of the messages must be 
chosen, the string returned by errorMsg e seems to be the useful one as 
s can be deduced from the structure of the program, at least in this 
example.
Regards,
Phil