Slides from LASER 2012

[Dmitry Olshansky]

On 21-Sep-12 03:27, Timon Gehr wrote:
> On 09/21/2012 12:51 AM, bearophile wrote:
>> Timon Gehr:
>>
>>> chain has type Result. dynRange takes an arbitrary range and transforms
>>> it into a range with the same value/vs reference behaviour whose static
>>> type depends only on the element type.
>>
>> I see. So that chain() is the normal chain of Phobos :-)
>>
>
> Exactly.
>
>> (But is DynRange a lazy stream/sequence? This is the most important
>> thing, because creating an eager linked list is kind of easy already,
>> and misses the main point of my "request".)
>>
>> Bye,
>> bearophile
>
> Proof of concept:
>
> import std.range, std.algorithm;
> struct DynRange(T){
>      @property T front(){ return frontImpl(); }
>      @property bool empty(){ return emptyImpl(); }
>      void popFront(){
>          auto u = popFrontImpl();
>          frontImpl = u.frontImpl;
>          emptyImpl = u.emptyImpl;
>          popFrontImpl = u.popFrontImpl;
>      }
> private:
>      T delegate() frontImpl;
>      bool delegate() emptyImpl;
>      DynRange!T delegate() popFrontImpl;
> }
> DynRange!(ElementType!R) dynRange(R)(R range)if(isInputRange!R){
>      DynRange!(ElementType!R) result;
>      result.frontImpl = ()=>range.front;
>      result.emptyImpl = ()=>range.empty;
>      result.popFrontImpl = (){
>          auto newRange = range;
>          newRange.popFront();
>          return dynRange(newRange);
>      };
>      return result;
> }
>
> void main(){
>      auto r = iota(0,10).dynRange;
>      auto t = [1,2,3,4,5].dynRange;
>      import std.stdio;
>      writeln(r,r,t,t);
> }
>
> To allow the definition of recursive lazy ranges, we'd also need
> a facility to 'delay' computation. I'll post a proof of concept
> tomorrow, by implementing eg. a lazy prime sieve.

I swear I've seen it somewhere in Phobos:
http://dlang.org/phobos/std_range.html#InputRangeObject
and friends. Maybe we ought to lay a better infrastructure for it.

-- 
Dmitry Olshansky