[m-dev.] for review: use bitsets in quantification

[Ralph Becket]

>From Fergus Henderson on 03/11/2000 08:45:04
> > +:- typeclass enum(T) where [
> > +	func to_int(T) = int,
> > +	func from_int(int) = T
> > +].
> 
> The documentation and interface here suggests that only types which
> are isomorphic to `int' are allowed, and that `from_int' can't fail.
> But I think the intent is that this typeclass should be allowed
> for types which are isomorphic to a subrange of `int'.
> The `from_int' function should be semidet, and you should
> document when it should fail.

I'd rather keep from_int/1 det and see an extra predicate or two added:

	pred int_is_enum_image(int::in) is semidet,
	pred convert_int(int::in, T::out) is semidet

Quite often (e.g. when converting between chars and ints) you know
that a conversion operation is going to succeed, so making semidet
the default mode would needlessly complicate such code.

> > +:- module sparse_bitset.
> ...
> > +	% `set__equal(SetA, SetB' is true iff `SetA' and `SetB'
> > +	% contain the same elements.
> > +:- pred equal(sparse_bitset(T), sparse_bitset(T)).
> > +:- mode equal(in, in) is semidet.
> 
> s/set__//

s/, SetB'/, SetB)'/

> > +	% `fold(Func, Set, Start)' calls Func with each element
> > +	% of `Set' and an accumulator (with the initial value of
> > +	% `Start'), and returns the final value.
> > +	% Takes O(NlogN) time.
> > +:- func fold(func(T, U) = U, sparse_bitset(T), U) = U <= enum(T).
> 
> You should document the order in which elements are processed.

I recently posted a draft spec. for collection types of which this
is obviously an instance.  It'd be nice if the interface to this
module conformed.

> It may be worth defining a generic `foldr' that traverses the elements
> in reverse order, and using that.

Seconded (see above comment).

One final remark: you include pred versions of the funcs - why?!

--
Ralph Becket      |      MSR Cambridge      |      rbeck at microsoft.com 

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