Comment by alpaca128

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);