(.module:
  [lux (#- function)
   ["_" test (#+ Test)]
   [abstract
    [monad (#+ do)]]
   [control
    [pipe (#+ case>)]]
   [data
    ["." maybe]
    ["." error (#+ Error)]
    [collection
     ["." list ("#@." functor)]]]
   [math
    ["r" random (#+ Random) ("#@." monad)]]
   [tool
    [compiler
     [analysis (#+ Arity)]
     ["." reference (#+ Register)]
     ["." synthesis (#+ Synthesis)]]]]
  ["." // #_
   ["#." case]
   [//
    [common (#+ Runner)]]])

(def: max-arity Arity 10)

(def: arity
  (Random Arity)
  (|> r.nat (r@map (|>> (n/% max-arity) (n/max 1)))))

(def: (local arity)
  (-> Arity (Random Register))
  (|> r.nat (r@map (|>> (n/% arity) inc))))

(def: function
  (Random [Arity Register Synthesis])
  (do r.monad
    [arity ..arity
     local (..local arity)]
    (wrap [arity local
           (synthesis.function/abstraction
            {#synthesis.environment (list)
             #synthesis.arity arity
             #synthesis.body (synthesis.variable/local local)})])))

(def: #export (spec run)
  (-> Runner Test)
  (do r.monad
    [[arity local functionS] ..function
     partial-arity (|> r.nat (:: @ map (|>> (n/% arity) (n/max 1))))
     inputs (r.list arity r.safe-frac)
     #let [expectation (maybe.assume (list.nth (dec local) inputs))
           inputsS (list@map (|>> synthesis.f64) inputs)]]
    ($_ _.and
        (_.test "Can read arguments."
                (|> (synthesis.function/apply {#synthesis.function functionS
                                               #synthesis.arguments inputsS})
                    (run "with-local")
                    (//case.verify expectation)))
        (_.test "Can partially apply functions."
                (or (n/= 1 arity)
                    (let [preS (list.take partial-arity inputsS)
                          postS (list.drop partial-arity inputsS)
                          partialS (synthesis.function/apply {#synthesis.function functionS
                                                              #synthesis.arguments preS})]
                      (|> (synthesis.function/apply {#synthesis.function partialS
                                                     #synthesis.arguments postS})
                          (run "partial-application")
                          (//case.verify expectation)))))
        (_.test "Can read environment."
                (or (n/= 1 arity)
                    (let [environment (|> partial-arity
                                          (list.n/range 1)
                                          (list@map (|>> #reference.Local)))
                          variableS (if (n/<= partial-arity local)
                                      (synthesis.variable/foreign (dec local))
                                      (synthesis.variable/local (|> local (n/- partial-arity))))
                          inner-arity (n/- partial-arity arity)
                          innerS (synthesis.function/abstraction
                                  {#synthesis.environment environment
                                   #synthesis.arity inner-arity
                                   #synthesis.body variableS})
                          outerS (synthesis.function/abstraction
                                  {#synthesis.environment (list)
                                   #synthesis.arity partial-arity
                                   #synthesis.body innerS})]
                      (|> (synthesis.function/apply {#synthesis.function outerS
                                                     #synthesis.arguments inputsS})
                          (run "with-foreign")
                          (//case.verify expectation)))))
        )))