Feature request: Conditional function chaining

[ceremcem]

I think it would be nice to have conditional function chaining, like the following:

a
  .x!
  .y! if foo
  .z!

...which will be compiled to:

var x$;
x$ = a;
x$ = x$.x();
if (foo) {
  x$ = x$.y();
}
x$ = x$.z();

This feature will be useful when we need a conditional middle step on a long function chain.

[anko]

For comparison, currently possible patterns:

1. Cascade with conditional:

   a
     ..x!
       (if foo then ..y! else ..)
         ..z!

   var x$, y$, z$;
   x$ = a;
   y$ = x$.x();
   z$ = foo ? y$.y() : y$;
   z$.z();

2. Pipe-chaining accessor functions:

   a
     |> (.x!)
     |> -> if foo then it.y! else it
     |> (.z!)

   (function(it){
     return it.z();
   })(
   function(it){
     if (foo) {
       return it.y();
     } else {
       return it;
     }
   }(
   function(it){
     return it.x();
   }(
   a)));

The suggested syntax would be clearer.