@super

[marcelocantos]

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Purpose

Please describe the end goal you are trying to achieve that has led you to request this feature.

As an extension to #485, support the special value @super, which refers to the lhs of a merge, either regular (some_tuple +> (y: @super.x + 1) equals some_tuple +> (y: some_tuple.x + 1)) or within special tuple/dict syntax (a +> (y+>: @super.x)) equals a +> (y+>: a.x))).

Chaining is not supported. Referring up the tree requires capturing in let forms:

some_tuple_expr +> (y+>: @super -> (z+>: @super.w + .x))

equals:

some_tuple_expr -> . +> (y+>: (z+>: .y.w + .x))

While the above hardly looks like an improvement, the existing syntax is still obviously not as clean

@super is purely a lexical construct. It is not part of the data model or execution model. Consequently, the following wouldn't work, because @super doesn't mean anything in the context in which it appears:

let merger = (y: @super.x + 1);
some_tuple +> merger

Suggested approaches

What have you tried, and how might this problem be solved?

The name @super was inspired by Jsonnet, from which this concept is lifted. A better name might be @lhs. I even considered just @, but I want to reserve that in case we implement the equivalent of Jsonnet's self, though that seems unlikely at this stage, since (a: 1, b: @.a + 1) can be trivially refactored as let a = 1; (:a, b: a + 1).