(assert=
  (let ((x 0)) (let loop () (when (< x 5) (set! x (+ x 1)) (loop))) x)
  5
  "set! counter in named let loop")

(assert=
  (let
    ((acc (list)))
    (let
      loop
      ((i 0))
      (when (< i 3) (set! acc (append acc (list i))) (loop (+ i 1))))
    acc)
  (list 0 1 2)
  "set! list accumulator in named let with param")

(assert=
  (let
    ((acc (list)) (i 0))
    (let loop () (when (< i 3) (append! acc i) (set! i (+ i 1)) (loop)))
    acc)
  (list 0 1 2)
  "append! + set! counter in named let")

(assert=
  (let
    ((sum 0))
    (let
      loop
      ((i 1))
      (when (<= i 10) (set! sum (+ sum i)) (loop (+ i 1))))
    sum)
  55
  "set! sum in named let loop (1..10)")

(assert=
  (let
    ((result ""))
    (let
      loop
      ((i 0))
      (when (< i 3) (set! result (str result (str i))) (loop (+ i 1))))
    result)
  "012"
  "set! string accumulator in named let")

(assert= (let ((x 0)) (set! x 42) x) 42 "set! in plain let (baseline)")

(assert=
  (let loop ((i 0) (acc 0)) (if (< i 5) (loop (+ i 1) (+ acc i)) acc))
  10
  "named let without set! (baseline)")