(;module:
  lux
  (lux (data [bool "bool/" Eq<Bool>]
             [text "text/" Eq<Text>]
             [number]
             (coll [list "list/" Fold<List>]))
       (meta [code "code/" Eq<Code>]))
  (luxc (lang ["la" analysis]
              ["ls" synthesis])
        (synthesizer ["&;" function])))

(def: #export (path pattern)
  (-> la;Pattern ls;Path)
  (case pattern
    (#la;BindP register)
    (` ("lux case bind" (~ (code;nat register))))
    
    (^template [<from> <to>]
      (<from> value)
      (<to> value))
    ([#la;BoolP code;bool]
     [#la;NatP  code;nat]
     [#la;IntP  code;int]
     [#la;DegP  code;deg]
     [#la;FracP code;frac]
     [#la;TextP code;text])
    
    (#la;TupleP membersP)
    (case (list;reverse membersP)
      #;Nil
      (' ("lux case pop"))

      (#;Cons singletonP #;Nil)
      (path singletonP)

      (#;Cons lastP prevsP)
      (let [length (list;size membersP)
            last-idx (n.dec length)
            [_ tuple-path] (list/fold (function [current-pattern [current-idx next-path]]
                                        [(n.dec current-idx)
                                         (` ("lux case seq"
                                             ("lux case tuple left" (~ (code;nat current-idx)) (~ (path current-pattern)))
                                             (~ next-path)))])
                                      [(n.dec last-idx)
                                       (` ("lux case tuple right" (~ (code;nat last-idx)) (~ (path lastP))))]
                                      prevsP)]
        tuple-path))
    
    (#la;VariantP tag num-tags memberP)
    (if (n.= (n.dec num-tags) tag)
      (` ("lux case variant right" (~ (code;nat tag)) (~ (path memberP))))
      (` ("lux case variant left" (~ (code;nat tag)) (~ (path memberP)))))))

(def: #export (weave leftP rightP)
  (-> ls;Path ls;Path ls;Path)
  (with-expansions [<default> (as-is (` ("lux case alt" (~ leftP) (~ rightP))))]
    (case [leftP rightP]
      (^template [<special>]
        (^ [[_ (#;Form (list [_ (#;Text <special>)] [_ (#;Nat left-idx)] left-then))]
            [_ (#;Form (list [_ (#;Text <special>)] [_ (#;Nat right-idx)] right-then))]])
        (if (n.= left-idx right-idx)
          (` (<special> (~ (code;nat left-idx)) (~ (weave left-then right-then))))
          <default>))
      (["lux case tuple left"]
       ["lux case tuple right"]
       ["lux case variant left"]
       ["lux case variant right"])

      (^ [[_ (#;Form (list [_ (#;Text "lux case seq")] left-pre left-post))]
          [_ (#;Form (list [_ (#;Text "lux case seq")] right-pre right-post))]])
      (case (weave left-pre right-pre)
        (^ [_ (#;Form (list [_ (#;Text "lux case alt")] _ _))])
        <default>

        weavedP
        (` ("lux case seq" (~ weavedP) (~ (weave left-post right-post)))))

      _
      (if (code/= leftP rightP)
        leftP
        <default>))))