with and alias keywords

[orenelbaum]

If we add placeholders to pipeline operators, we could do something similar to old JS's with:

very.long.expression
  |> ^.a = ^.b + 1

We could also maybe support assignment:

very.long.expression
  |> ^ = ^ + 1
//  ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
very.long.expression = very.long.expression + 1

although this is not necessarily as straight forward as it might seem.

I'm proposing reviving the with keyword, but unlike the old with, use it with placeholders to make it less terrible, and make it assignable.

with very.long.expression
  ^ = ^ + 1
  if (^ > 3) return ^

This could support aliases and multiple parameters:

with (a = some.long.expression, b = another.long.expression)
  if (a > 3) a = b + 1
  else b = a + 1

Or with a combination of an alias and placeholders for documentation purposes

with (coolNumber = an.array.with.lots.of.numbers[5])
  if (* > 5) console.log 'big!'
  else if (* < 2) console.log 'small.'

Also like if and for, this could support implicit return and being used as an expression.

A related proposal, made by @edemaine, is alias declarations, that introduce a binding to the current scope.

alias x = very.long.expression
if (x > 2) x = 1
//  ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
if (very.long.expression > 2) very.long.expression = 1

This is pretty powerful and could even be used to create reactive variables similar to Svelte:

alias sig = createSignal().val
if (sig > 2) sig = 1
//  ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
const ref = createSignal()
if (ref.val > 2) ref.val = 1

Both proposals have nuances and I think there's a lot to think about, but I also think that they could be very handy in some situations.