At

https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L43

I've implemented a function either() with behaviour similar to the `or` function/operator in dynamic languages such as Python and Lisp.

I'm almost satisified with it except that the lazy evaluation at

https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L45

cannot be made nothrow.

If I qualify the function as nothrow DMD complains as

algorithm_ex.d(45,16): Error: 'a' is not nothrow
algorithm_ex.d(46,29): Error: '_param_1' is not nothrow

I don't see a reason why any of these two cases should throw.

The same problem occurs if I make the implementation use only one function and check the recursion termination case with `static if (bs.length == 1)` instead.

Is there a workaround for this?

On Thursday, 14 May 2015 at 09:53:20 UTC, Per Nordlöw wrote:
> At
>
> https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L43
>
> I've implemented a function either() with behaviour similar to the `or` function/operator in dynamic languages such as Python and Lisp.
>
> I'm almost satisified with it except that the lazy evaluation at
>
> https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L45
>
> cannot be made nothrow.
>
> If I qualify the function as nothrow DMD complains as
>
> algorithm_ex.d(45,16): Error: 'a' is not nothrow
> algorithm_ex.d(46,29): Error: '_param_1' is not nothrow
>
> I don't see a reason why any of these two cases should throw.

Lazy argument is essentially delegate/function. Currently there is no
way to mark it as nothrow.

> The same problem occurs if I make the implementation use only one function and check the recursion termination case with `static if (bs.length == 1)` instead.
>
> Is there a workaround for this?

One way to address is to use delegate explicitly.

int foo(lazy int a) //nothrow
{
	return a;
}

int bar(int delegate() nothrow dg) nothrow
{
	return dg();
}

void main() nothrow
{
	int a;
	bar(()=>a);
}

On Thursday, 14 May 2015 at 10:18:13 UTC, Maxim Fomin wrote:
> On Thursday, 14 May 2015 at 09:53:20 UTC, Per Nordlöw wrote:
>> At
>>
>> https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L43
>>
>> I've implemented a function either() with behaviour similar to the `or` function/operator in dynamic languages such as Python and Lisp.
>>
>> I'm almost satisified with it except that the lazy evaluation at
>>
>> https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L45
>>
>> cannot be made nothrow.
>>
>> If I qualify the function as nothrow DMD complains as
>>
>> algorithm_ex.d(45,16): Error: 'a' is not nothrow
>> algorithm_ex.d(46,29): Error: '_param_1' is not nothrow
>>
>> I don't see a reason why any of these two cases should throw.
>
> Lazy argument is essentially delegate/function. Currently there is no
> way to mark it as nothrow.
>
>> The same problem occurs if I make the implementation use only one function and check the recursion termination case with `static if (bs.length == 1)` instead.
>>
>> Is there a workaround for this?
>
> One way to address is to use delegate explicitly.
>
> int foo(lazy int a) //nothrow
> {
> 	return a;
> }
>
> int bar(int delegate() nothrow dg) nothrow
> {
> 	return dg();
> }
>
> void main() nothrow
> {
> 	int a;
> 	bar(()=>a);
> }

That does not feel right at all. D's filosophy is to infer these things.Are you saying that I should create to overloads for the leaf case of either(), namely one that takes a nothrow delegate as argument and another overload that handles the throw case. Further you example functions are not templates. either() must be a template. Could you please show how to modify either() to use your delegate-version instead.

On Thursday, 14 May 2015 at 09:53:20 UTC, Per Nordlöw wrote:
> I'm almost satisified with it except that the lazy evaluation at
>
> https://github.com/nordlow/justd/blob/master/algorithm_ex.d#L45
>
> cannot be made nothrow.
>
> If I qualify the function as nothrow DMD complains as
>
> algorithm_ex.d(45,16): Error: 'a' is not nothrow
> algorithm_ex.d(46,29): Error: '_param_1' is not nothrow


https://issues.dlang.org/show_bug.cgi?id=12647