Banjo

First-class messages

(Inspired by Elm's .foo syntax to create a field accessor function)

It would be very useful to support a method call whose target hasn't been specified yet, as a kind of currying. It should support acting as a getter or a setter, so maybe:

.y = {
  (x) = x.y
  lazy(x) = -> x.y
  setter(x) = {(val) = x {+} {y = val}}}
  mapper(f) = {(x) = x {+} {y = f(x.y)}}
}

.foo(bar) = [
  (x) = x.foo(bar)
  lazy(x) = -> x.foo(bar)
  setter(x) = ... // ???
}

The setter is useful for higher-order functions where you want to create a function that replaces a field in its parameter with new value.

The mapper transforms the single field to give a new object where just that field was replaced.