[Hat] Pattern match errors in do?

[Malcolm Wallace]

"Neil Mitchell" <ndmitchell at gmail.com> wrote:

> Running Main without any arguments via Hat gives me a trace, and the
> error message:
> > Error: pattern-match failure in do expression
> 
> Running hat-stack Main.hat gives me:
> > Tracefile "Main.hat" contains no reference to a program error.

Very strange.  The tracefile contains the error message (at the end),
and an explicit reference to it (in bytes 8-11).  But it contains no
reference (in bytes 4-7) to the expression that triggered the error, and
so hat-stack quite reasonably complains.

It looks like the library code to trap the error and tidy up the
tracefile might have a bug.

Regards,
    Malcolm