is(x = module) vs. __traits(isModule, x)

[Paul Backus]

On Wednesday, 7 October 2020 at 20:08:02 UTC, Stefan Koch wrote:
> On Wednesday, 7 October 2020 at 19:15:30 UTC, Paul Backus wrote:
>>
>> Here's my strawman proposal: turn all __traits into 
>> properties. A few before-and-after examples:
>>
>> __traits(isModule, foo)
>>   => foo.__isModule
>>
>> __traits(getMember, T, "x")
>>   => T.__member("x")
>>
>> __traits(compiles, some(kind, of + expression))
>>   => (some(kind, of + expression)).__compiles
>
> I don't think that looks much better.
> __traits are actually fine in my eyes.
> It's easy on semantic and parser.
> Determining whether a trait applies and therefore should be 
> imported into the properties of a given node is more nasty.
> (It means you have to change semanticX and semanticY as well as 
> resolvePropertiesX in DMD)

Couldn't you unconditionally lower <Node>.__isModule to 
__traits(isModule, <Node>) regardless of what type of node it is, 
and rely on the existing error messages for incorrect trait 
arguments? You don't have to worry about shadowing "real" 
properties, because anything that starts with "__" is a reserved 
identifier.