Tuple expression for .to(def)

[ssalbdivad]

There is an existing tuple expression for morphs (using "=>"), but it accepts a function as the second param.

.to is a helpful sugar that allows providing a validated definition, but there's no way to provide a validated definition to the expression, which could be helpful especially for inlining defs in a scope.

I'd like to determine what that would look like- either an extension of "=>" with an alternate index 2 shape letting us know it's a definition, or a new operator.