Hello.

------
MyType increment(MyType previous)
{
	//snip
}

auto myRec = std.range.recurrence!increment(initialMyType);
-----

... doesn't work. What am I doing wrong? The documentation doesn't seem to imply the function has to be passed as a string, if that's the issue.

On Tuesday, 19 February 2013 at 10:37:31 UTC, n00b wrote:
> Hello.
>
> ------
> MyType increment(MyType previous)
> {
> 	//snip
> }
>
> auto myRec = std.range.recurrence!increment(initialMyType);
> -----
>
> ... doesn't work. What am I doing wrong? The documentation doesn't seem to imply the function has to be passed as a string, if that's the issue.

It is not very well documented (or should I say, documented at all...), but the signature of a recurrence function must take the form:

"auto recurrence(R)(R r, size_t n);"

Where:
n is the current index being calculated and:
r is a range that holds the values of your recurrence, and is valid for the indices "n - 1" to "n - numberOfInitialArgs". The type of R is implementation defined. (It's a "Cycle!(T[Args.length])" for efficiency reasons, fyi, but this is an implementation detail).

For example, fibs and ! would be implemented as such:

//----
import std.stdio;
import std.range;

int fibFun(R)(R r, size_t n)
{
    return r[n - 1] + r[n - 2];
}
int expFun(R)(R r, size_t n)
{
    return n * r[n - 1];
}

void main()
{
    //auto myRec = std.range.recurrence!(increment)('a', 'b');
    auto fib = std.range.recurrence!fibFun(1, 1);
    auto exp = std.range.recurrence!expFun(1);
    writeln(fib.take(10));
    writeln(exp.take(10));
}
//----
[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
//----

Le 19/02/2013 07:09, monarch_dodra a écrit :
> On Tuesday, 19 February 2013 at 10:37:31 UTC, n00b wrote:
>> Hello.
>>
>> ------
>> MyType increment(MyType previous)
>> {
>> //snip
>> }
>>
>> auto myRec = std.range.recurrence!increment(initialMyType);
>> -----
>>
>> ... doesn't work. What am I doing wrong? The documentation doesn't
>> seem to imply the function has to be passed as a string, if that's the
>> issue.
>
> It is not very well documented (or should I say, documented at all...),
> but the signature of a recurrence function must take the form:
>
> "auto recurrence(R)(R r, size_t n);"
>
> Where:
> n is the current index being calculated and:
> r is a range that holds the values of your recurrence, and is valid for
> the indices "n - 1" to "n - numberOfInitialArgs". The type of R is
> implementation defined. (It's a "Cycle!(T[Args.length])" for efficiency
> reasons, fyi, but this is an implementation detail).
>
> For example, fibs and ! would be implemented as such:
>
> //----
> import std.stdio;
> import std.range;
>
> int fibFun(R)(R r, size_t n)
> {
> return r[n - 1] + r[n - 2];
> }
> int expFun(R)(R r, size_t n)
> {
> return n * r[n - 1];
> }
>
> void main()
> {
> //auto myRec = std.range.recurrence!(increment)('a', 'b');
> auto fib = std.range.recurrence!fibFun(1, 1);
> auto exp = std.range.recurrence!expFun(1);
> writeln(fib.take(10));
> writeln(exp.take(10));
> }
> //----
> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
> [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
> //----


Thanks a lot. I reported the lack of documentation to bugzilla, I hope I did it right...^^