The following code now works and illustrates some good points
of typeclasses. It also shows a problem:
//////////////////////////////////////////
#import <flx.flxh>
include "stl";
open Reversible_Sequence[
Stl::Vector::stl_vector[int],
Stl::Vector::stl_vector_iterator[int],
Stl::Vector::stl_vector_reverse_iterator[int],
int
];
var x: Stl::Vector::stl_vector[int];
print$ empty x; endl;
open Stl::Vector;
push_back (x,4);
push_back (x,5);
push_back (x,6);
insert (x,begin x,3);
insert (x,end x,7);
insert (x,begin x,2);
insert (x,begin x,1);
print$ empty x; endl;
proc check[c,it,rit with Reversible_Sequence[c,it,rit,int]]
{
// forward iterator: forwards
var i = begin x;
whilst i != end x do
print$ *i; endl;
i++;
done;
// forward iterator: backwards
i = end x;
whilst i != begin x do
i--;
print$ *i; endl;
done;
// reverse iterator: forwards
var j = rbegin x;
whilst j != rend x do
print$ *j; endl;
j++;
done;
// reverse iterator: backwards
j = rend x;
whilst j != rbegin x do
j--;
print$ *j; endl;
done;
}
check [
Stl::Vector::stl_vector[int],
Stl::Vector::stl_vector_iterator[int],
Stl::Vector::stl_vector_reverse_iterator[int],
int
]();
//////////////////////////////////////////
What's cute is that the 'check' procedure is generic:
it will work on any Reversible_Sequence, not just vector.
The restriction to 'int' is simply because we don't have a Show[t]
typeclass for converting types to strings.
What isn't cute is the need to do this:
open Reversible_Sequence[
Stl::Vector::stl_vector[int],
Stl::Vector::stl_vector_iterator[int],
Stl::Vector::stl_vector_reverse_iterator[int],
int
];
just so that
print$ empty x; endl;
works. What we wanted was this:
Reversible_Sequence[
Stl::Vector::stl_vector[int],
Stl::Vector::stl_vector_iterator[int],
Stl::Vector::stl_vector_reverse_iterator[int],
int
]::empty x;
We can open a typeclass .. but we can't use a specialisation
of one as a qualifier in a qualified name. We can of course do:
fun empty[with Reversible_Sequence[
Stl::Vector::stl_vector[int],
Stl::Vector::stl_vector_iterator[int],
Stl::Vector::stl_vector_reverse_iterator[int],
int
]] (x:stl_vector[int]) => empty x;
to work around this .. perhaps even with an anonymous lambda
(not sure if you can have polymorphic lambdas ..).
It seems absurd you can't access a typeclass function directly.
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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