[MLton] Option to show path map

[Vesa Karvonen]

Quoting Stephen Weeks <sweeks at sweeks.com>:
[...]
> I wonder if, to be consistent with -show-basis and -show-def-use, it
> would be better to make it
> 
>   -show-path-map <file>
> 
> rather than
> 
>   -show-path-map {false|true}
> 
> And, for consistency, don't exit after writing the data to a file.

I did wonder about the same thing.  Note that -show-path-map behaves
like -show-anns.  Personally, I'd prefer that the output would go to
stdout so that scripts wouldn't have to deal with temporary files and
that there would be no argument to the option.  IOW, you would just
write

  mlton [...] -show-anns

or

  mlton [...] -show-path-map

and you'd get the output.  It would probably make sense to use a
different naming convention for such options (or commands), e.g.
-print-anns and -print-path-map.

-Vesa Karvonen