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1 point by akkartik 545 days ago | link | parent

What are the semantics of `lets` exactly? Do you have to alternate binding forms with 'body' expressions?

2 points by rocketnia 545 days ago | link

No, you can interleave bindings and body expressions however you like, but the catch is that you can't use destructuring bindings since they look like expressions. It works like this:

  (lets) -> nil
  (lets a) -> a
  (lets a b . rest) ->
    If `a` is ssyntax or a non-symbol, we treat it as an expression:
      (do a (lets b . rest))
    Otherwise, we treat it as a variable to bind:
      (let a b (lets . rest))
The choice is almost forced in each case. It almost never makes sense to use an ssyntax symbol in a variable binding, and it almost never makes sense to discard the result of an expression that's just a variable name.

The implementation is here in Lathe's arc/utils.arc:

Current link:

Posterity link: