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digitalmars.D.learn - Cannot Qualify Variadic Functions with Lazy Arguments as nothrow

reply "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
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?
May 14 2015
next sibling parent reply "Maxim Fomin" <maxim-fomin outlook.com> writes:
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);
}
May 14 2015
parent "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
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.
May 14 2015
prev sibling parent "anonymous" <anonymous example.com> writes:
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
May 14 2015