Thread overview | |||||||||
---|---|---|---|---|---|---|---|---|---|
|
January 08, 2011 Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
eg. to return a fibonacci delegate: return (ulong m) { if(m < 2) return m ; return _self_ref(m-1)+_self_ref(m-2) ; } ; Is it possible? Thank you! |
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to tsukikage | On 01/08/2011 04:45 PM, tsukikage wrote: > eg. to return a fibonacci delegate: > > return (ulong m) { > if(m < 2) return m ; > return _self_ref(m-1)+_self_ref(m-2) ; > } ; > > Is it possible? Thank you! http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator I don't think there's a built in way to self-recurse. |
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to Pelle | As a workaround you can do this for now: import std.stdio; enum deleg = returnFib(); ulong delegate(ulong m) returnFib() { return (ulong m) { if(m < 2) return m; return deleg(m-1)+deleg(m-2); }; } void main() { writeln(returnFib()(10)); } Otherwise I'd really like the ability for a lambda to call itself. Perhaps a feature request is in order. |
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to Pelle | On 08/01/2011 16:00, Pelle wrote:
<snip>
> http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator
<snip>
How are you getting around D not supporting recursively defined types?
Stewart.
|
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to Andrej Mitrovic | On 08/01/2011 17:40, Andrej Mitrovic wrote:
<snip>
> Otherwise I'd really like the ability for a lambda to call itself.
> Perhaps a feature request is in order.
I'm not sure what D would gain in practice. If you want a function that calls itself, why not just name the function?
Stewart.
|
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to Stewart Gordon | On 1/8/11, Stewart Gordon <smjg_1998@yahoo.com> wrote:
> On 08/01/2011 17:40, Andrej Mitrovic wrote:
> <snip>
>> Otherwise I'd really like the ability for a lambda to call itself. Perhaps a feature request is in order.
>
> I'm not sure what D would gain in practice. If you want a function that calls itself, why not just name the function?
>
> Stewart.
>
I don't know. Perhaps it would be useful in generics..
|
January 08, 2011 Re: Calling anonymous delegate recursively ? | ||||
---|---|---|---|---|
| ||||
Posted in reply to Pelle | Thank Pelle , and others. I'm thinking ways to do this task : http://rosettacode.org/wiki/Anonymous_recursion With this last version of Y-combinator http://rosettacode.org/wiki/Y_combinator#D , it look like this: ulong fib(long n) { if(n < 0) throw new Exception("No negative") ; return Y((ulong delegate(ulong) self) { return (ulong m) { return (m <= 1) ? m : self(m-1) + self(m-2) ; } ; })(n) ; } and works. Only that this Y-combinator seems induced a lot of overhead(four return statements in the Y's definition). From D document, if i not misunderstood, a delegate has 2 property .ptr (frame pointer) and .funcptr (address of function), so the delegate should be a structure? Would there be a hack to get access to this structure? It seems not now. Thanks again. Pelle wrote: > On 01/08/2011 04:45 PM, tsukikage wrote: >> eg. to return a fibonacci delegate: >> >> return (ulong m) { >> if(m < 2) return m ; >> return _self_ref(m-1)+_self_ref(m-2) ; >> } ; >> >> Is it possible? Thank you! > > http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator > > I don't think there's a built in way to self-recurse. |
Copyright © 1999-2021 by the D Language Foundation