On Mon, 2004-02-02 at 23:23, Alain.Frisch@ens.fr wrote:
> On Sun, 1 Feb 2004, Yaron M. Minsky wrote:
> 
> > Does anyone know why there's no support for Big_int comparisons?
> 

> A solution could be to allow attaching custom generic operations to
> non-custom blocks 

The problem with this is you end up re-implementing Python,
i.e. having a 'vector' of generic functions for each type.
Another 'useful' generic operator is of course 'get next'
for containers (C++ iterators, Python sequence operators ..)

Now, Ocaml does provide the tools to deal with this in most cases:
functors (provided the genericity is not required to be run-time). 

The problem then would seem to be that
its hard to write functors for every data structure,
sub-data structure of the data stucture, etc.

At least part of the reason is that the functors
provide abstract types, so building a functor
to provide, for example, a comparator so you 
can put them in sets isn't immediately compatible
with other generic operations such as pattern matching.

It seems like the 'private' keyword is a step forward here:
a way to control representation invariants during construction
(or mutation) which doesn't prevent convenient algrebraic
type destructors like pattern matching being used: even though,
in principle, these operations may not retain their semantics,
for example a type

	int * int

representing a rational number admits the destructor

	fst v

which is not in fact a projection (since the type
is not a product).


-- 
John Max Skaller, mailto:skaller@tpg.com.au
snail:25/85c Wigram Rd, Glebe, NSW 2037, Australia.
voice:61-2-9660-0850. Checkout Felix: http://felix.sf.net




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