DIP19: Remove comma operator from D and provision better syntactic support for tuples

[bearophile]

> I have appreciated named fields of D tuples since the 
> beginning, I have found them quite handy. With them sometimes 
> you don't need to unpack a tuple, you can just access its 
> fields with a nice name, avoiding to move around more than one 
> variable.

In Haskell to solve this problem there is the @ syntax for 
tuples. As an example usage, this Haskell function vNorm 
normalizes a Vec (a 2D vector). Its input is a Vec, that is 
unpacked in its x and y fields, but vNorm al gives a name to the 
whole input Vec, naming it 'v'. So you are able to call the other 
function vLen with no need to pack again x and y in a Vec:

vLen :: Vec -> Double
vLen x = sqrt $ vDot x x

vNorm :: Vec -> Vec
vNorm v@(Vec x y) = Vec (x / l) (y / l) where l = vLen v

(In my first post in this thread I have not listed such extra 
features for tuples because I think they are less important than 
a good unpacking syntax in those four cases.)

Bye,
bearophile