[Ocaml-lib-devel] Enum inconsistent

[John S. <sk...@oz...>]

The current Enum module seems inconsistent.
The interplay between force, count, etc
make the point in time at which user
supplied next function is called indeterminate.

That isn't really acceptable, since the enumeration
is conceptually a model of a mutable object:
even though the enum module itself is functional,
it is being used to contruct mutator functions
which operate on a stateful object.

The fast_count function must be elided:
it is a symptom of the designer not being
able to make up his mind exactly what
the model is.

This is non-trivial. The only way to count
a filtered enumeration is eagerly,
on the other hand next can be applied lazily.

In particular: it must be specified not only if
count consumes an emumeration, but also if
it forces lazy operations. Both questions
must have a definite answer.

The same is probably true for all other operations,
however in most cases the answer is obvious.

The point in time a next function supplied
to make is called is of vital interest
to the client and must be predictable
due to side effects on the object being
enumerated.

There are several possible ways to resolve
this issue, it is a nasty problem, but expected
since the entity being modelled is stateful,
and the client is providing mutators to the
Enum module.

The [from] function is the biggest hassle,
I'd consider removing it. The client can
always use

	init f limit

which also might turn accidental infinite loops
into merely very long ones :-)

-- 
John Max Skaller, mailto:sk...@oz...
snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia.
voice:61-2-9660-0850