Hi Olivier,
Actually I do have TextPad and I get: "Cannot find key 'TextPad\shell\open\ddeexec\application' in registration database (error 2)" which, as I said in my first email, is the same error that I get when trying "winhugs /edit" from the command line. I speculated that was the command because that is the HKEY_CLASSES_ROOT\hugs_haskell\shell\Edit\command key but it is clear that more happens under the cover after that.
Under Options, TextPad is already the selected editor, so that doesn't help me. The (grayed out) command is "C:\Programme\ Textpad 5\System\DDEOPN32.EXE TextPad %s(%d)". Trying to execute that from the Windows shell gives the same error as above.
The fact that running the TextPad command gives a registry error means it's TextPad that is at fault. I know roughly what WinHugs does, but have absolutely no idea what TextPad does. The command is grayed out because it was automatically inferred, but change to a custom editor and you can edit it. All WinHugs does on /edit is invoke whatever that command line is after substituting %s for the filename and %d for the line number.
I think the mistake is to look for a TextPad entry: there isn't one. Instead there are Textpad.dde and TextPad.tws entries and I guess Textpad.dde is the correct one since it has the shell\open\ddeexec\application key. But whose mistake is it: TextPad's or WinHugs' and how does one go about fixing it?
TextPad is at fault. You can work round the textpad bug by changing the editor command line to something else, or try and bring it up in the TextPad support forum. Or try reinstalling TextPad. Thanks, Neil