(if-let (op1 ...)
  (if-let (op2 ...)
    ...
  err1
err2

(if-let [res (some-> arg
                     op1
                     op2)]
  res
  somethin-failed) ;; what failed though?

(some-with-err-> arg
                 op1 err1
                 op2 err2
                 ...)