We need to have a way to say "convert this nested function into a struct"

[via Digitalmars-d]

On Saturday, 6 June 2015 at 13:44:51 UTC, Jacob Carlborg wrote:
> On 2015-06-06 08:59, Jonathan M Davis wrote:
>> On Saturday, 6 June 2015 at 06:16:17 UTC, Andrei Alexandrescu 
>> wrote:
>>> Nested functions that allocate their environment dynamically 
>>> can be
>>> quite useful. However, oftentimes the need is to convert the 
>>> code plus
>>> the data needed into an anonymous struct that copies the 
>>> state inside,
>>> similar to C++ lambdas that capture by value.
>>>
>>> I wonder how to integrate that within the language nicely.
>>
>> Some of us were discussing this at dconf. Essentially, we need 
>> a way to
>> create a functor similar to how C++ lambdas do. The most 
>> straightforward
>> way would involve string mixins, and you'd do something like
>>
>> auto f = makeFunctor!"function code here"(arguments);
>
> Which could look like this with AST macros ;)
>
> auto f = makeFunctor(args) {
>    function code goes here, no strings are needed
> }

Well, this kind of syntax can be implemented without AST macros. 
But there are syntactic ambiguities if the delegate has 
parameters:

auto f = makeFunctor(args) (a, b) { }

Is the second pair of parens the delegate's parameter list, or a 
call a callable object returned by makeFunctor?

Besides, do we require a semicolon after the closing brace? If 
yes, that would be at odds with the rest of the language, but if 
not, we cannot easily chain such calls...