How does `let` work in Scheme?

While not exactly the problem you’re experiencing, but an aside based on your questioning about the sequence of evaluating the arguments, let is also “syntactic sugar” for a lambda followed by it’s arguments that are first evaluated and then passed to the lambda which is then evaluated.

For instance:

(let ((a (list 1 2 3))
      (b (list 4 5 6)))
     (cons a b))

is the same as:

((lambda (list-a list-b) (cons list-a list-b)) (list 1 2 3) (list 4 5 6))

So, if you’re ever wondering about evaluation sequence, the arguments are evaluated fully before the body is evaluated (and one argument cannot refer to an argument preceding it … use let* for something that requires bindings like that).

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