Impressed

[Graham Fawcett]

On Friday, 27 July 2012 at 13:10:46 UTC, Stuart wrote:
> On Friday, 27 July 2012 at 03:00:25 UTC, Brad Anderson wrote:
>>
>> D equivalent: iota(0, int.max, 2).map!(a => /* do something 
>> with even numbers */)();
>
> I think you're missing the point. The purpose isn't to generate 
> a sequence of numbers, but to illustrate how the Yield keyword 
> is used in VB.NET. Sure, getting a sequence of numbers may be 
> straightforward, but what about a lazy-populated list of all 
> files on a computer? That can be done using Yield - and more 
> importantly, WRITTEN like a normal synchronous function. Let's 
> see you do that with map.

That's easy:

import std.file, std.stdio, std.algorithm;

void main()
{
   static BASE_DIR = "/path/to/base";
   static SIZE_CUTOFF = 100;

   // 'entries' is an InputRange

   auto entries = dirEntries(BASE_DIR, SpanMode.breadth);

   // filter the range; map to a range of filenames

   auto smallFileNames = entries
     .filter!(e => e.size < SIZE_CUTOFF)
     .map!(e => e.name);

   // note, the filesystem hasn't been touched yet;
   // we have full laziness.

   foreach(name; smallFileNames)
     writeln(name);
}


And check out this example, where you can process the entries in 
parallel:

http://dlang.org/phobos/std_file.html#dirEntries

You should spend some time using ranges before drawing 
conclusions about them.

Graham