;;  Copyright (c) Eduardo Julian. All rights reserved.
;;  This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
;;  If a copy of the MPL was not distributed with this file,
;;  You can obtain one at http://mozilla.org/MPL/2.0/.

(ns lux.analyser.lux
  (:require (clojure [template :refer [do-template]]
                     [set :as set])
            clojure.core.match
            clojure.core.match.array
            (lux [base :as & :refer [|do return return* fail fail* |let |list |case]]
                 [parser :as &parser]
                 [type :as &type]
                 [host :as &host])
            (lux.analyser [base :as &&]
                          [lambda :as &&lambda]
                          [case :as &&case]
                          [env :as &&env]
                          [module :as &&module]
                          [record :as &&record]
                          [meta :as &&meta])))

;; [Utils]
;; TODO: Walk the type to set up the bound-type, instead of doing a
;; rough calculation like this one.
(defn ^:private count-univq [type]
  "(-> Type Int)"
  (|case type
    (&/$UnivQ env type*)
    (inc (count-univq type*))

    _
    0))

;; TODO: This technique won't work if the body of the type contains
;; nested quantifications that cannot be directly counted.
(defn ^:private next-bound-type [type]
  "(-> Type Type)"
  (&/$BoundT (->> (count-univq type) (* 2) (+ 1))))

(defn ^:private embed-inferred-input [input output]
  "(-> Type Type Type)"
  (|case output
    (&/$UnivQ env output*)
    (&/$UnivQ env (embed-inferred-input input output*))

    _
    (&/$LambdaT input output)))

;; [Exports]
(defn analyse-unit [analyse ?exo-type]
  (|do [_cursor &/cursor
        _ (&type/check ?exo-type &/$UnitT)]
    (return (&/|list (&&/|meta ?exo-type _cursor
                               (&&/$tuple (&/|list)))))))

(defn analyse-tuple [analyse ?exo-type ?elems]
  (|case ?elems
    (&/$Nil)
    (analyse-unit analyse (|case ?exo-type
                            (&/$Left exo-type) exo-type
                            (&/$Right exo-type) exo-type))

    (&/$Cons ?elem (&/$Nil))
    (analyse (|case ?exo-type
               (&/$Left exo-type) exo-type
               (&/$Right exo-type) exo-type)
             ?elem)

    _
    (|case ?exo-type
      (&/$Left exo-type)
      (|do [exo-type* (&type/actual-type exo-type)]
        (|case exo-type*
          (&/$UnivQ _)
          (&type/with-var
            (fn [$var]
              (|do [exo-type** (&type/apply-type exo-type* $var)
                    [[tuple-type tuple-cursor] tuple-analysis] (&&/cap-1 (analyse-tuple analyse (&/$Left exo-type**) ?elems))
                    =var (&type/resolve-type $var)
                    inferred-type (|case =var
                                    (&/$VarT iid)
                                    (|do [:let [=var* (next-bound-type tuple-type)]
                                          _ (&type/set-var iid =var*)
                                          tuple-type* (&type/clean $var tuple-type)]
                                      (return (&/$UnivQ &/$Nil tuple-type*)))

                                    _
                                    (&type/clean $var tuple-type))]
                (return (&/|list (&&/|meta inferred-type tuple-cursor
                                           tuple-analysis))))))

          _
          (analyse-tuple analyse (&/$Right exo-type*) ?elems)))

      (&/$Right exo-type)
      (|do [unknown? (&type/unknown? exo-type)]
        (if unknown?
          (|do [=elems (&/map% #(|do [=analysis (&&/analyse-1+ analyse %)]
                                  (return =analysis))
                               ?elems)
                _ (&type/check exo-type (|case (->> (&/|map &&/expr-type* =elems) (&/|reverse))
                                          (&/$Cons last prevs)
                                          (&/fold (fn [right left] (&/$ProdT left right))
                                                  last prevs)))
                _cursor &/cursor]
            (return (&/|list (&&/|meta exo-type _cursor
                                       (&&/$tuple =elems)
                                       ))))
          (|do [exo-type* (&type/actual-type exo-type)]
            (&/with-attempt
              (|case exo-type*
                (&/$ProdT _)
                (|let [num-elems (&/|length ?elems)
                       [_shorter _tuple-types] (&type/tuple-types-for num-elems exo-type*)]
                  (if (= num-elems _shorter)
                    (|do [=elems (&/map2% (fn [elem-t elem]
                                            (&&/analyse-1 analyse elem-t elem))
                                          _tuple-types
                                          ?elems)
                          _cursor &/cursor]
                      (return (&/|list (&&/|meta exo-type _cursor
                                                 (&&/$tuple =elems)
                                                 ))))
                    (|do [=direct-elems (&/map2% (fn [elem-t elem] (&&/analyse-1 analyse elem-t elem))
                                                 (&/|take (dec _shorter) _tuple-types)
                                                 (&/|take (dec _shorter) ?elems))
                          =indirect-elems (analyse-tuple analyse
                                                         (&/$Right (&/|last _tuple-types))
                                                         (&/|drop (dec _shorter) ?elems))
                          _cursor &/cursor]
                      (return (&/|list (&&/|meta exo-type _cursor
                                                 (&&/$tuple (&/|++ =direct-elems =indirect-elems))
                                                 ))))))

                (&/$ExQ _)
                (&type/with-var
                  (fn [$var]
                    (|do [exo-type** (&type/apply-type exo-type* $var)
                          [[tuple-type tuple-cursor] tuple-analysis] (&&/cap-1 (analyse-tuple analyse (&/$Right exo-type**) ?elems))
                          =tuple-analysis (&&/clean-analysis $var (&&/|meta exo-type tuple-cursor
                                                                            tuple-analysis))]
                      (return (&/|list =tuple-analysis)))))

                (&/$UnivQ _)
                (|do [$var &type/existential
                      :let [(&/$ExT $var-id) $var]
                      exo-type** (&type/apply-type exo-type* $var)
                      [[tuple-type tuple-cursor] tuple-analysis] (&/with-scope-type-var $var-id
                                                                   (&&/cap-1 (analyse-tuple analyse (&/$Right exo-type**) ?elems)))]
                  (return (&/|list (&&/|meta exo-type tuple-cursor
                                             tuple-analysis))))

                _
                (&/fail-with-loc (str "[Analyser Error] Tuples require tuple-types: " (&type/show-type exo-type*)))
                )
              (fn [err]
                (&/fail-with-loc (str err "\n" "[Analyser Error] Tuples require tuple-types: " (&type/show-type exo-type)))))))))
    ))

(defn ^:private analyse-variant-body [analyse exo-type ?values]
  (|do [_cursor &/cursor
        output (|case ?values
                 (&/$Nil)
                 (analyse-unit analyse exo-type)

                 (&/$Cons ?value (&/$Nil))
                 (analyse exo-type ?value)

                 _
                 (analyse-tuple analyse (&/$Right exo-type) ?values))]
    (|case output
      (&/$Cons x (&/$Nil))
      (return x)

      _
      (&/fail-with-loc "[Analyser Error] Can't expand to other than 1 element."))))

(defn analyse-variant [analyse ?exo-type idx is-last? ?values]
  (|case ?exo-type
    (&/$Left exo-type)
    (|do [exo-type* (&type/actual-type exo-type)]
      (|case exo-type*
        (&/$UnivQ _)
        (&type/with-var
          (fn [$var]
            (|do [exo-type** (&type/apply-type exo-type* $var)
                  [[variant-type variant-cursor] variant-analysis] (&&/cap-1 (analyse-variant analyse (&/$Left exo-type**) idx is-last? ?values))
                  =var (&type/resolve-type $var)
                  inferred-type (|case =var
                                  (&/$VarT iid)
                                  (|do [:let [=var* (next-bound-type variant-type)]
                                        _ (&type/set-var iid =var*)
                                        variant-type* (&type/clean $var variant-type)]
                                    (return (&/$UnivQ &/$Nil variant-type*)))

                                  _
                                  (&type/clean $var variant-type))]
              (return (&/|list (&&/|meta inferred-type variant-cursor
                                         variant-analysis))))))

        _
        (analyse-variant analyse (&/$Right exo-type*) idx is-last? ?values)))

    (&/$Right exo-type)
    (|do [exo-type* (|case exo-type
                      (&/$VarT ?id)
                      (&/try-all% (&/|list (|do [exo-type* (&type/deref ?id)]
                                             (&type/actual-type exo-type*))
                                           (|do [_ (&type/set-var ?id &type/Type)]
                                             (&type/actual-type &type/Type))))

                      _
                      (&type/actual-type exo-type))]
      (&/with-attempt
        (|case exo-type*
          (&/$SumT _)
          (|do [vtype (&type/sum-at idx exo-type*)
                :let [num-variant-types (&/|length (&type/flatten-sum exo-type*))
                      is-last?* (if (nil? is-last?)
                                  (= idx (dec num-variant-types))
                                  is-last?)]
                =value (analyse-variant-body analyse vtype ?values)
                _cursor &/cursor]
            (if (= 1 num-variant-types)
              (return (&/|list =value))
              (return (&/|list (&&/|meta exo-type _cursor (&&/$variant idx is-last?* =value))))
              ))

          (&/$UnivQ _)
          (|do [$var &type/existential
                exo-type** (&type/apply-type exo-type* $var)]
            (analyse-variant analyse (&/$Right exo-type**) idx is-last? ?values))

          (&/$ExQ _)
          (&type/with-var
            (fn [$var]
              (|do [exo-type** (&type/apply-type exo-type* $var)
                    =exprs (analyse-variant analyse (&/$Right exo-type**) idx is-last? ?values)]
                (&/map% (partial &&/clean-analysis $var) =exprs))))
          
          _
          (&/fail-with-loc (str "[Analyser Error] Can't create variant if the expected type is " (&type/show-type exo-type*) " " idx " " (->> ?values (&/|map &/show-ast) (&/|interpose " ") (&/fold str "")))))
        (fn [err]
          (|case exo-type
            (&/$VarT ?id)
            (|do [=exo-type (&type/deref ?id)]
              (&/fail-with-loc (str err "\n" "[Analyser Error] Can't create variant if the expected type is " (&type/show-type =exo-type) " " idx " " (->> ?values (&/|map &/show-ast) (&/|interpose " ") (&/fold str "")))))

            _
            (&/fail-with-loc (str err "\n" "[Analyser Error] Can't create variant if the expected type is " (&type/show-type exo-type) " " idx " " (->> ?values (&/|map &/show-ast) (&/|interpose " ") (&/fold str "")))))))
      )))

(defn analyse-record [analyse exo-type ?elems]
  (|do [[rec-members rec-type] (&&record/order-record ?elems)]
    (|case exo-type
      (&/$VarT id)
      (|do [? (&type/bound? id)]
        (if ?
          (analyse-tuple analyse (&/$Right exo-type) rec-members)
          (|do [[[tuple-type tuple-cursor] tuple-analysis] (&&/cap-1 (analyse-tuple analyse (&/$Left rec-type) rec-members))
                _ (&type/check exo-type tuple-type)]
            (return (&/|list (&&/|meta exo-type tuple-cursor
                                       tuple-analysis))))))

      _
      (analyse-tuple analyse (&/$Right exo-type) rec-members)
      )))

(defn ^:private analyse-global [analyse exo-type module name]
  (|do [[[r-module r-name] [endo-type ?meta ?value]] (&&module/find-def module name)
        ;; This is a small shortcut to optimize analysis of typing code.
        _ (if (and (clojure.lang.Util/identical &type/Type endo-type)
                   (clojure.lang.Util/identical &type/Type exo-type))
            (return nil)
            (&type/check exo-type endo-type))
        _cursor &/cursor]
    (return (&/|list (&&/|meta endo-type _cursor
                               (&&/$var (&/$Global (&/T [r-module r-name]))))))))

(defn ^:private analyse-local [analyse exo-type name]
  (fn [state]
    (|let [stack (&/get$ &/$scopes state)
           no-binding? #(and (->> % (&/get$ &/$locals)  (&/get$ &/$mappings) (&/|contains? name) not)
                             (->> % (&/get$ &/$closure) (&/get$ &/$mappings) (&/|contains? name) not))
           [inner outer] (&/|split-with no-binding? stack)]
      (|case outer
        (&/$Nil)
        (&/run-state (|do [module-name &/get-module-name]
                       (analyse-global analyse exo-type module-name name))
                     state)

        (&/$Cons ?genv (&/$Nil))
        (if-let [global (->> ?genv (&/get$ &/$locals) (&/get$ &/$mappings) (&/|get name))]
          (|case global
            [(&/$Global ?module* name*) _]
            (&/run-state (analyse-global analyse exo-type ?module* name*)
                         state)

            _
            (fail* "[Analyser Error] Can't have anything other than a global def in the global environment."))
          (fail* (str "[Analyser Error] Unknown global definition: " name)))
        
        (&/$Cons bottom-outer _)
        (|let [scopes (&/|map #(&/get$ &/$name %) (&/|reverse inner))
               [=local inner*] (&/fold2 (fn [register+new-inner frame in-scope]
                                          (|let [[register new-inner] register+new-inner
                                                 [register* frame*] (&&lambda/close-over in-scope name register frame)]
                                            (&/T [register* (&/$Cons frame* new-inner)])))
                                        (&/T [(or (->> bottom-outer (&/get$ &/$locals)  (&/get$ &/$mappings) (&/|get name))
                                                  (->> bottom-outer (&/get$ &/$closure) (&/get$ &/$mappings) (&/|get name)))
                                              &/$Nil])
                                        (&/|reverse inner) scopes)]
          ((|do [_ (&type/check exo-type (&&/expr-type* =local))]
             (return (&/|list =local)))
           (&/set$ &/$scopes (&/|++ inner* outer) state)))
        ))))

(defn analyse-symbol [analyse exo-type ident]
  (|do [:let [[?module ?name] ident]]
    (if (= "" ?module)
      (analyse-local analyse exo-type ?name)
      (analyse-global analyse exo-type ?module ?name))
    ))

(defn ^:private analyse-apply* [analyse exo-type fun-type ?args]
  (|case ?args
    (&/$Nil)
    (|do [_ (&type/check exo-type fun-type)]
      (return (&/T [fun-type &/$Nil])))
    
    (&/$Cons ?arg ?args*)
    (|do [?fun-type* (&type/actual-type fun-type)]
      (&/with-attempt
        (|case ?fun-type*
          (&/$UnivQ _)
          (&type/with-var
            (fn [$var]
              (|do [type* (&type/apply-type ?fun-type* $var)
                    [=output-t =args] (analyse-apply* analyse exo-type type* ?args)
                    ==args (&/map% (partial &&/clean-analysis $var) =args)]
                (|case $var
                  (&/$VarT ?id)
                  (|do [? (&type/bound? ?id)
                        type** (if ?
                                 (&type/clean $var =output-t)
                                 (|do [_ (&type/set-var ?id (next-bound-type =output-t))
                                       cleaned-output* (&type/clean $var =output-t)
                                       :let [cleaned-output (&/$UnivQ &/$Nil cleaned-output*)]]
                                   (return cleaned-output)))
                        _ (&type/clean $var exo-type)]
                    (return (&/T [type** ==args])))
                  ))))

          (&/$ExQ _)
          (|do [$var &type/existential
                type* (&type/apply-type ?fun-type* $var)]
            (analyse-apply* analyse exo-type type* ?args))

          (&/$LambdaT ?input-t ?output-t)
          (|do [[=output-t =args] (analyse-apply* analyse exo-type ?output-t ?args*)
                =arg (&/with-attempt
                       (&&/analyse-1 analyse ?input-t ?arg)
                       (fn [err]
                         (&/fail-with-loc (str err "\n" "[Analyser Error] Function expected: " (&type/show-type ?input-t)))))]
            (return (&/T [=output-t (&/$Cons =arg =args)])))

          _
          (&/fail-with-loc (str "[Analyser Error] Can't apply a non-function: " (&type/show-type ?fun-type*))))
        (fn [err]
          (&/fail-with-loc (str err "\n" "[Analyser Error] Can't apply function " (&type/show-type fun-type) " to args: " (->> ?args (&/|map &/show-ast) (&/|interpose " ") (&/fold str "")))))))
    ))

(defn ^:private do-analyse-apply [analyse exo-type =fn ?args]
  (|do [:let [[[=fn-type =fn-cursor] =fn-form] =fn]
        [=output-t =args] (analyse-apply* analyse exo-type =fn-type ?args)]
    (return (&/|list (&&/|meta =output-t =fn-cursor
                               (&&/$apply =fn =args)
                               )))))

(defn analyse-apply [analyse cursor exo-type =fn ?args]
  (|do [loader &/loader
        :let [[[=fn-type =fn-cursor] =fn-form] =fn]]
    (|case =fn-form
      (&&/$var (&/$Global ?module ?name))
      (|do [[real-name [?type ?meta ?value]] (&&module/find-def ?module ?name)]
        (|case (&&meta/meta-get &&meta/macro?-tag ?meta)
          (&/$Some _)
          (|do [macro-expansion (fn [state]
                                  (|case (-> ?value (.apply ?args) (.apply state))
                                    (&/$Right state* output)
                                    (&/$Right (&/T [state* output]))

                                    (&/$Left error)
                                    ((&/fail-with-loc error) state)))
                module-name &/get-module-name
                ;; :let [[r-prefix r-name] real-name
                ;;       _ (when (or (= "actor:" r-name)
                ;;                   ;; (= "|Codec@Json|" r-name)
                ;;                   ;; (= "|Codec@Json//encode|" r-name)
                ;;                   ;; (= "|Codec@Json//decode|" r-name)
                ;;                   ;; (= "derived:" r-name)
                ;;                   )
                ;;           (->> (&/|map &/show-ast macro-expansion)
                ;;                (&/|interpose "\n")
                ;;                (&/fold str "")
                ;;                (prn (&/ident->text real-name) module-name)))
                ;;       ]
                ]
            (&/flat-map% (partial analyse exo-type) macro-expansion))

          _
          (do-analyse-apply analyse exo-type =fn ?args)))
      
      _
      (do-analyse-apply analyse exo-type =fn ?args))
    ))

(defn analyse-case [analyse exo-type ?value ?branches]
  (|do [:let [num-branches (&/|length ?branches)]
        _ (&/assert! (> num-branches 0) "[Analyser Error] Can't have empty branches in \"case\" expression.")
        _ (&/assert! (even? num-branches) "[Analyser Error] Unbalanced branches in \"case\" expression.")
        =value (&&/analyse-1+ analyse ?value)
        :let [var?? (|case =value
                      [_ (&&/$var =var-kind)]
                      (&/$Some =value)

                      _
                      &/$None)]
        =match (&&case/analyse-branches analyse exo-type var?? (&&/expr-type* =value) (&/|as-pairs ?branches))
        _cursor &/cursor]
    (return (&/|list (&&/|meta exo-type _cursor
                               (&&/$case =value =match)
                               )))))

(defn ^:private unravel-inf-appt [type]
  (|case type
    (&/$AppT =input+ (&/$VarT _inf-var))
    (&/$Cons _inf-var (unravel-inf-appt =input+))

    _
    (&/|list)))

(defn ^:private clean-func-inference [$input $output =input =func]
  (|case =input
    (&/$VarT iid)
    (|do [:let [=input* (next-bound-type =func)]
          _ (&type/set-var iid =input*)
          =func* (&type/clean $input =func)
          =func** (&type/clean $output =func*)]
      (return (&/$UnivQ &/$Nil =func**)))
    
    (&/$AppT =input+ (&/$VarT _inf-var))
    (&/fold% (fn [_func _inf-var]
               (|do [:let [$inf-var (&/$VarT _inf-var)]
                     =inf-var (&type/resolve-type $inf-var)
                     _func* (clean-func-inference $inf-var $output =inf-var _func)
                     _ (&type/delete-var _inf-var)]
                 (return _func*)))
             =func
             (unravel-inf-appt =input))

    (&/$ProdT _ _)
    (&/fold% (fn [_func _inf-var]
               (|do [:let [$inf-var (&/$VarT _inf-var)]
                     =inf-var (&type/resolve-type $inf-var)
                     _func* (clean-func-inference $inf-var $output =inf-var _func)
                     _ (&type/delete-var _inf-var)]
                 (return _func*)))
             =func
             (&/|reverse (&type/flatten-prod =input)))
    
    _
    (|do [=func* (&type/clean $input =func)
          =func** (&type/clean $output =func*)]
      (return =func**))))

(defn analyse-lambda* [analyse exo-type ?self ?arg ?body]
  (|case exo-type
    (&/$VarT id)
    (|do [? (&type/bound? id)]
      (if ?
        (|do [exo-type* (&type/deref id)]
          (analyse-lambda* analyse exo-type* ?self ?arg ?body))
        ;; Inference
        (&type/with-var
          (fn [$input]
            (&type/with-var
              (fn [$output]
                (|do [[[lambda-type lambda-cursor] lambda-analysis] (analyse-lambda* analyse (&/$LambdaT $input $output) ?self ?arg ?body)
                      =input (&type/resolve-type $input)
                      =output (&type/resolve-type $output)
                      inferred-type (clean-func-inference $input $output =input (embed-inferred-input =input =output))
                      _ (&type/check exo-type inferred-type)]
                  (return (&&/|meta inferred-type lambda-cursor
                                    lambda-analysis)))
                ))))))

    _
    (&/with-attempt
      (|do [exo-type* (&type/actual-type exo-type)]
        (|case exo-type*
          (&/$UnivQ _)
          (|do [$var &type/existential
                :let [(&/$ExT $var-id) $var]
                exo-type** (&type/apply-type exo-type* $var)]
            (&/with-scope-type-var $var-id
              (analyse-lambda* analyse exo-type** ?self ?arg ?body)))

          (&/$ExQ _)
          (&type/with-var
            (fn [$var]
              (|do [exo-type** (&type/apply-type exo-type* $var)
                    =expr (analyse-lambda* analyse exo-type** ?self ?arg ?body)]
                (&&/clean-analysis $var =expr))))
          
          (&/$LambdaT ?arg-t ?return-t)
          (|do [[=scope =captured =body] (&&lambda/with-lambda ?self exo-type*
                                           ?arg ?arg-t
                                           (&&/analyse-1 analyse ?return-t ?body))
                _cursor &/cursor
                register-offset &&env/next-local-idx]
            (return (&&/|meta exo-type* _cursor
                              (&&/$lambda register-offset =scope =captured =body))))

          _
          (fail "")))
      (fn [err]
        (&/fail-with-loc (str err "\n" "[Analyser Error] Functions require function types: " (&type/show-type exo-type)))))
    ))

(defn analyse-lambda** [analyse exo-type ?self ?arg ?body]
  (|case exo-type
    (&/$UnivQ _)
    (|do [$var &type/existential
          :let [(&/$ExT $var-id) $var]
          exo-type* (&type/apply-type exo-type $var)
          [_ _expr] (&/with-scope-type-var $var-id
                      (analyse-lambda** analyse exo-type* ?self ?arg ?body))
          _cursor &/cursor]
      (return (&&/|meta exo-type _cursor _expr)))
    
    (&/$VarT id)
    (|do [? (&type/bound? id)]
      (if ?
        (|do [exo-type* (&type/actual-type exo-type)]
          (analyse-lambda* analyse exo-type* ?self ?arg ?body))
        ;; Inference
        (analyse-lambda* analyse exo-type ?self ?arg ?body)))
    
    _
    (|do [exo-type* (&type/actual-type exo-type)]
      (analyse-lambda* analyse exo-type* ?self ?arg ?body))
    ))

(defn analyse-lambda [analyse exo-type ?self ?arg ?body]
  (|do [output (&/with-no-catches
                 (analyse-lambda** analyse exo-type ?self ?arg ?body))]
    (return (&/|list output))))

(defn analyse-def [analyse optimize eval! compile-def ?name ?value ?meta]
  (|do [_ &/ensure-statement
        module-name &/get-module-name
        ? (&&module/defined? module-name ?name)]
    (if ?
      (&/fail-with-loc (str "[Analyser Error] Can't redefine " (str module-name ";" ?name)))
      (|do [=value (&/without-repl-closure
                    (&/with-scope ?name
                      (&&/analyse-1+ analyse ?value)))
            =meta (&&/analyse-1 analyse &type/Anns ?meta)
            ==meta (eval! (optimize =meta))
            _ (&&module/test-type module-name ?name ==meta (&&/expr-type* =value))
            _ (&&module/test-macro module-name ?name ==meta (&&/expr-type* =value))
            _ (compile-def ?name (optimize =value) ==meta)]
        (return &/$Nil))
      )))

(defn ^:private merge-hosts
  "(-> Host Host Host)"
  [new old]
  (|let [merged-module-states (&/fold (fn [total m-state]
                                        (|let [[_name _state] m-state]
                                          (|case _state
                                            (&/$Cached)
                                            (&/|put _name _state total)
                                            
                                            (&/$Compiled)
                                            (&/|put _name _state total)

                                            _
                                            total)))
                                      (&/get$ &/$module-states old)
                                      (&/get$ &/$module-states new))]
    (->> old
         (&/set$ &/$module-states merged-module-states))))

(defn ^:private merge-modules
  "(-> Text Module Module Module)"
  [current-module new old]
  (&/fold (fn [total* entry]
            (|let [[_name _module] entry]
              (if (or (= current-module _name)
                      (->> _module
                           (&/get$ &&module/$defs)
                           &/|length
                           (= 0)))
                ;; Don't modify the entry of the current module, to
                ;; avoid overwritting it's data in improper ways.
                ;; Since it's assumed the "original" old module
                ;; contains all the proper own-module information.
                total*
                (&/|put _name _module total*))))
          old new))

(defn ^:private merge-compilers
  "(-> Text Compiler Compiler Compiler)"
  [current-module new old]
  (->> old
       (&/set$ &/$modules (merge-modules current-module
                                         (&/get$ &/$modules new)
                                         (&/get$ &/$modules old)))
       (&/set$ &/$seed (max (&/get$ &/$seed new)
                            (&/get$ &/$seed old)))
       (&/set$ &/$host (merge-hosts (&/get$ &/$host new)
                                    (&/get$ &/$host old)))))

(def ^:private get-compiler
  (fn [compiler]
    (return* compiler compiler)))

(defn ^:private set-compiler [compiler*]
  (fn [_]
    (return* compiler* compiler*)))

(defn analyse-module [analyse optimize eval! compile-module ?meta]
  (|do [_ &/ensure-statement
        =anns (&&/analyse-1 analyse &type/Anns ?meta)
        ==anns (eval! (optimize =anns))
        module-name &/get-module-name
        _ (&&module/set-anns ==anns module-name)
        _imports (&&module/fetch-imports ==anns)
        current-module &/get-module-name
        ;; =asyncs (&/map% (fn [_import]
        ;;                   (|let [[path alias] _import]
        ;;                     (&/without-repl
        ;;                      (&/save-module
        ;;                       (|do [_ (if (= current-module path)
        ;;                                 (&/fail-with-loc (str "[Analyser Error] Module can't import itself: " path))
        ;;                                 (return nil))
        ;;                             already-compiled? (&&module/exists? path)
        ;;                             active? (&/active-module? path)
        ;;                             _ (&/assert! (not active?)
        ;;                                          (str "[Analyser Error] Can't import a module that is mid-compilation: " path " @ " current-module))
        ;;                             _ (&&module/add-import path)
        ;;                             ?async (if (not already-compiled?)
        ;;                                      (compile-module path)
        ;;                                      (|do [_compiler get-compiler]
        ;;                                        (return (doto (promise)
        ;;                                                  (deliver (&/$Right _compiler))))))
        ;;                             _ (if (= "" alias)
        ;;                                 (return nil)
        ;;                                 (&&module/alias current-module alias path))]
        ;;                         (return ?async))))))
        ;;                 _imports)
        ;; _compiler get-compiler
        ;; ;; Some type-vars in the typing environment stay in
        ;; ;; the environment forever, making type-checking slower.
        ;; ;; The merging process for compilers more-or-less "fixes" the
        ;; ;; problem by resetting the typing enviroment, but ideally
        ;; ;; those type-vars shouldn't survive in the first place.
        ;; ;; TODO: MUST FIX
        ;; _ (&/fold% (fn [compiler _async]
        ;;              (|case @_async
        ;;                (&/$Right _new-compiler)
        ;;                (set-compiler (merge-compilers current-module _new-compiler compiler))

        ;;                (&/$Left ?error)
        ;;                (fail ?error)))
        ;;            _compiler
        ;;            =asyncs)
        ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
        _ (&/map% (fn [_import]
                    (|let [[path alias] _import]
                      (&/without-repl
                       (&/save-module
                        (|do [_ (if (= current-module path)
                                  (&/fail-with-loc (str "[Analyser Error] Module can't import itself: " path))
                                  (return nil))
                              already-compiled? (&&module/exists? path)
                              active? (&/active-module? path)
                              _ (&/assert! (not active?)
                                           (str "[Analyser Error] Can't import a module that is mid-compilation: " path " @ " current-module))
                              _ (&&module/add-import path)
                              _ (if (not already-compiled?)
                                  (compile-module path)
                                  (return nil))
                              _ (if (= "" alias)
                                  (return nil)
                                  (&&module/alias current-module alias path))]
                          (return nil))))))
                  _imports)]
    (return &/$Nil)))

(defn ^:private coerce [new-type analysis]
  "(-> Type Analysis Analysis)"
  (|let [[[_type _cursor] _analysis] analysis]
    (&&/|meta new-type _cursor
              _analysis)))

(defn analyse-ann [analyse eval! exo-type ?type ?value]
  (|do [=type (&&/analyse-1 analyse &type/Type ?type)
        ==type (eval! =type)
        _ (&type/check exo-type ==type)
        =value (&/with-expected-type ==type
                 (&&/analyse-1 analyse ==type ?value))
        _cursor &/cursor]
    (return (&/|list (&&/|meta ==type _cursor
                               (&&/$ann =value =type)
                               )))))

(defn analyse-coerce [analyse eval! exo-type ?type ?value]
  (|do [=type (&&/analyse-1 analyse &type/Type ?type)
        ==type (eval! =type)
        _ (&type/check exo-type ==type)
        =value (&&/analyse-1+ analyse ?value)]
    (return (&/|list (coerce ==type =value)))))

(let [input-type (&/$AppT &type/List &type/Text)
      output-type (&/$AppT &type/IO &/$UnitT)]
  (defn analyse-program [analyse optimize compile-program ?args ?body]
    (|do [_ &/ensure-statement
          =body (&/with-scope ""
                  (&&env/with-local ?args input-type
                    (&&/analyse-1 analyse output-type ?body)))
          _ (compile-program (optimize =body))]
      (return &/$Nil))))