I like the lispiness and features of ITERATE but it breaks source location for debugging errors in SBCL with SLIME. Instead the ITER form is indicated, which dampens my enthusiasm for it somewhat.

  (defpackage :test
    (:use :cl :iterate))

  (in-package :test)

  (defun test-iter ()
    (declare (optimize (debug 3) (safety 3) (speed 0)))
    (iter:iter   ;;; <-- highlights whole ITER form
      (sleep 2)
      (error "test")))

  (defun test-loop ()
    (declare (optimize (debug 3) (safety 3) (speed 0)))
    (loop
      :do (sleep 2)
      :do (error "test")))   ;;; <-- highlights ERROR form