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<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-western">Hi
Mark,
<br>
<br>
<br>
it's a great adventure to explore Mercury; to understand more and more
and
<br>
to gain confidence steadily!
<br>
<br>
Of course I knew I was going to experiment with daring workarounds, and
I think
<br>
the work you are planning to do will present an even more satisfying
solution - so,
<br>
I guess, it's time for some patience...
<br>
<br>
If there are some `stupid' tasks to be done for assisting you, I would
be happy if <br>
you would
let me know...
<br>
<br>
But anyway, I can wait - it is definitely worth the time... <span
class="moz-smiley-s3"><span> ;-) </span></span>
<br>
<br>
<br>
All the best,
<br>
<br>
Nick
<br>
<br>
<blockquote type="cite">As mentioned near the start of section 10.2 of
the reference manual,
<br>
the types appearing in instances must be constructors with distinct
type
<br>
variables as arguments. The problem here is that T is not distinct --
it
<br>
appears twice in the arguments of fringeW/2.
<br>
<br>
We'd really like to lift this restriction, but it's deeply built into
the
<br>
implementation and is not likely to be lifted any time soon.
<br>
<br>
The compiler really should be reporting this error properly. That's a
<br>
compiler bug (and I'm surprised we haven't noticed this before, since
the
<br>
code that is supposed to do this check has been there for a long time).
<br>
We can at least fix the error reporting without too much trouble.
<br>
<br>
Hope that helps.
<br>
<br>
Cheers,
<br>
Mark.
<br>
<br>
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