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Comment by alpaca128 | Hacker News Reader

The scope is clearly defined by the parentheses, though if you're not used to Lisp syntax that can be confusing at first.

    (let n 12)                 =>  let n = 12;
    (let res (square a))       =>  let res = a*a;
    (let mod3 (eq 0 (% i 3)))  =>  let mod3 = (0 == i % 3);

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In Lisp, "let" is only used for binding the variable, and it comes with a scope.

  (let ((a 1)
        (b 2))
    (+ a b))

It's closer to the ML version of let, which works like this:

  let
      val a = 1
      val b = 2
  in
      a + b
  end

You can sequence expressions for side effects, as well.

  (let ((a 1)
        (b 2))
    (incf a)
    (do-it a b)
    (+ a b))

> The scope is clearly defined by the parentheses, though if you're not used to Lisp syntax that can be confusing at first.

The scope is clearly not defined by the parentheses, and I've been programming in Common Lisp for 25 years, so I'm pretty used to Lisp syntax.

A sibling comment suggests it comes from the JavaScript let (which did not exist when I learned JavaScript; it wasn't introduced until 1.7), which is scoped to the containing lexical block, rather than a block introduced by the let form itself.

Those lets in TFA seem more like Lisp’s setq rather than let. A let expression would bind values to names only within the scope of (let …) itself. The lets in TFA and in your examples have side effects. You reference the bound values outside of (let …).

In other lisps a let form has a body that the binding(s) range over and they are not available outside. As in `(let n 12 (+ n n))` here n wouldn't be accessible after. You have `(def name 5)` for making definitions that are readable outsude.

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