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February 19, 2013 Recurrence | ||||
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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. |
February 19, 2013 Re: Recurrence | ||||
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Posted in reply to n00b | 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] //---- |
February 19, 2013 Re: Recurrence | ||||
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Posted in reply to monarch_dodra | 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...^^
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