(define-module (hnh util values)
  :use-module (ice-9 control)
  :use-module (hnh util lens)
  :export (abort* on-fst on-snd
                  on-nth
                  value-ref
                  value-refx
                  apply/values))


(define-syntax-rule (abort* form)
  (call-with-values (lambda () form) abort))


;; (on-fst (+ 2 (abort* (values 3 4))))
;; ⇒ 5 ⇒ 4

(define-syntax-rule (on-fst form)
  (% form
     (lambda (prompt fst . rest)
       (apply values (prompt fst) rest))))

(define-syntax-rule (on-snd form)
  (% form
     (lambda (prompt fst snd . rest)
       (apply values fst (prompt snd) rest))))

(define-syntax-rule (on-nth idx form)
  (% form
     (lambda (prompt . rets)
       (apply values (modify rets (ref idx) prompt)))))

(define-syntax-rule (value-ref form idx)
  (call-with-values (lambda () form)
    (lambda returns (list-ref returns idx))))

(define-syntax-rule (value-refx idx form)
  (value-ref form idx))

;; TODO replace this with apply/mv from srfi-210
(define-syntax-rule (apply/values proc form)
  (call-with-values (lambda () form)
    proc))