(.module:
  lux
  (lux (data (coll [list "list/" Functor<List>]))))

(def: #export Variable Int)
(def: #export Register Nat)

(def: #export (captured register)
  (-> Register Variable)
  (|> register n/inc nat-to-int (i/* -1)))

(def: #export (local register)
  (-> Register Variable)
  (nat-to-int register))

(def: #export (local-register variable)
  (-> Variable Register)
  (int-to-nat variable))

(def: #export (captured-register variable)
  (-> Variable Register)
  (|> variable (i/* -1) int-to-nat n/dec))

(do-template [<name> <comp>]
  [(def: #export (<name> var)
     (-> Variable Bool)
     (<comp> 0 var))]

  [self?     i/=]
  [local?    i/>]
  [captured? i/<]
  )

(def: #export (from-ref ref)
  (-> Ref Variable)
  (case ref
    (#.Local register)
    (local register)
    
    (#.Captured register)
    (captured register)))

(def: #export (environment scope)
  (-> Scope (List Variable))
  (|> scope
      (get@ [#.captured #.mappings])
      (list/map (function (_ [_ [_ ref]]) (from-ref ref)))))