Curious thoughts, regarding functional programming

[Jacob Carlborg]

On 2011-10-12 22:56, Nick Sabalausky wrote:
> "Jacob Carlborg"<doob at me.com>  wrote in message
> news:j740a6$2t8m$1 at digitalmars.com...
>>
>> When this delegate is called you want to both be able to just return from
>> the delegate but also return from "foo".
>>
>> iterate(1, 10 ; int a)
>> {
>>      if (a == 2)
>> yield; // soft return, just returns from the delegate
>>
>>      else if (a == 4)
>>          return; // hard return, return from both the delegate and the
>> function that called the delegate
>> }
>>
>> Currently we only have "soft" returns from delegates.
>>
>
> Better (IMHO):
>
> void foo()
> {
>      iterate(int a; 1, 10)
>      {
>          if (a == 2)
>              continue; // return from just the delegate
>
>          else if (a == 4)
>              break; // return from both delegate and iterate
>
>          else if (a == 6)
>              return; // return from the delegate, iterate, and foo
>      }
> }

That's actually how it works in Ruby as well. Ruby also has both lambdas 
and blocks, the only difference between them is that you can't 
return/break from a lambda but you can from a block (I hope I got this 
right).

This answer to a stack overflow question explains how it works in Ruby:

http://stackoverflow.com/questions/1402757/how-to-break-out-from-a-ruby-block#answer-1402764 


> Ie, same syntax and semantics as foreach. Also, a couple new things that
> foreach doesn't have to deal with:
>
> auto x = map(i; 1, 10)
> {
>      //continue; // Error: map's dg can't return void
>      continue i*2; // OK
> }
> assert(x == [2, 4, 6, etc...]); // Conventiently ignoring ranges just for
> the sake of illustration
>
> Of course, maybe it would be better to require "yield" in such a case (and
> maybe make "yield" synonymous with "continue" for void delegates?), but
> there's a lot of resistance against new keywords.

Yeah, I know that.

> And, one last thing to take care of:
>
> auto x = iterate(i; 1, 10)
> {
>      if(i == 4)
>      {
>          //break; // Error: need a return value
>          break i*2; // OK
>      }
> }
> assert(x == 8);

Yeah, assuming "iterate" takes a delegate that returns something. But 
that would be nice, to create, what look like, statements that return a 
values.

-- 
/Jacob Carlborg