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

(type: #export #rec Primitive
  #Unit
  (#Bool Bool)
  (#Nat Nat)
  (#Int Int)
  (#Deg Deg)
  (#Frac Frac)
  (#Text Text))

(type: #export Tag Nat)

(type: #export (Composite a)
  (#Sum (Either a a))
  (#Product [a a]))

(type: #export Register Nat)

(type: #export #rec Pattern
  (#Simple Primitive)
  (#Complex (Composite Pattern))
  (#Bind Register))

(type: #export Variable
  (#Local Register)
  (#Foreign Register))

(type: #export (Match p e)
  [[p e] (List [p e])])

(type: #export Environment
  (List Variable))

(type: #export (Special e)
  [Text (List e)])

(type: #export #rec Analysis
  (#Primitive Primitive)
  (#Structure (Composite Analysis))
  (#Case Analysis (Match Pattern Analysis))
  (#Function Environment Analysis)
  (#Apply Analysis Analysis)
  (#Variable Variable)
  (#Constant Ident)
  (#Special (Special Text)))

## Variants get analysed as binary sum types for the sake of semantic
## simplicity.
## This is because you can encode a variant of any size using just
## binary sums by nesting them.

(do-template [<name> <tag>]
  [(def: <name>
     (-> Analysis Analysis)
     (|>> <tag> #Sum #Structure))]

  [left #.Left]
  [right #.Right]
  )

(def: (last? size tag)
  (-> Nat Tag Bool)
  (n/= (dec size) tag))

(def: #export (no-op value)
  (-> Analysis Analysis)
  (let [identity (#Function (list) (#Variable (#Local +1)))]
    (#Apply value identity)))

(def: #export (sum tag size temp value)
  (-> Tag Nat Register Analysis Analysis)
  (if (last? size tag)
    (if (n/= +1 tag)
      (..right value)
      (list/fold (function.const ..left)
                 (..right value)
                 (list.n/range +0 (n/- +2 tag))))
    (list/fold (function.const ..left)
               (case value
                 (#Structure (#Sum _))
                 (no-op value)

                 _
                 value)
               (list.n/range +0 tag))))

(def: #export (tuple members)
  (-> (List Analysis) Analysis)
  (case (list.reverse members)
    #.Nil
    (#Primitive #Unit)

    (#.Cons singleton #.Nil)
    singleton

    (#.Cons last prevs)
    (list/fold (function (_ left right) (#Structure (#Product left right)))
               last prevs)))

(def: #export (apply args func)
  (-> (List Analysis) Analysis Analysis)
  (list/fold (function (_ arg func) (#Apply arg func)) func args))

(type: #export Analyser
  (-> Code (Meta Analysis)))