Bernie Pope answered:
> > 1. Why do the rules of the monomorphism restriction explicitly mention
> > *simple* pattern bindings?
> > Where is the difference, especially as there is a translation to
> > simple pattern bindings?
> > Why should
> >
> > p | "a"=="b" = 2
> > | otherwise = 3
> >
> > be treated different than
> >
> > p = if "a"=="b" then 2 else 3
>
>
> They are the same (both are simple pattern bindings). The report says
> in section 4.4.3.2 that the first can be translated into the second.
Indeed, I meant to allude to this translation.
> A simple pattern binding is one where the lhs is a variable only.
That's consistent with the second reason for rule one of the MR.
However, the mentioned section 4.4.3.2 defines it differently:
A simple pattern binding has form p = e.
And if there is any doubt about what p stands for, it goes on:
The pattern p ...
Contrasting to that:
The general form of a pattern binding is p match, where a match is the same
structure as for function bindings above; in other words, a pattern binding
is:
p | g1 = e1
| g2 = e2
...
| gm = em
where { decls }
So according to this definition, a pattern binding is simple iff
there are no guards (unless they are in the expression).
Also the translation to a "simple pattern binding" only gets rid of guards.
So there seems to be an error in the report, which can be fixed by either
redefining "simple pattern binding", or using a differnet description in the
MR.
Bye
Christian Sievers
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