たけとんさんの書いたeitherで遊んでみた

gistfile1.scm

(define $maybe
  (lambda [$a]
    (matcher {
      ;; <primitive-pp> 
      [,$val [a] {[$tgt 
        (match [val tgt] [(maybe a) (maybe a)] {
          [[<just $x> <just ,x>] {[x]}]
          [[<nothing> <nothing>] {[]}]
          [_ {}]})]}]
      ;; <primitive-dp> 
      [<just $> [a] {[<Just $x> {[x]}] [_ {}]}]
      [<nothing> [] {[<Nothing> {[]}] [_ {}]}]})))

(define $either
  (lambda [$a $b]
    (matcher {
      ;; <primitive-pp>
      [,$val [a b] {[$tgt
        (match [val tgt] [(either a b) (either a b)] {
          [[<left $x> <left ,x>] {[x]}]
          [[<right $y> <right ,y>] {[y]}]
          [_ {}]
        })
      ]}]
      ;; <primitive-dp>
      [<left $> [a] {
        [<Left $x> {[x]}]
        [_ {}]
      }]
      [<right $> [b] {
        [<Right $x> {[x]}]
        [_ {}]
      }]
    })
  )
)

(test "------------")
(define $my-func
  (lambda $x 
    (match x (either (maybe string) (list integer)) {
      [<left <just _>>        <Pattern1>]
      [<left <nothing>>       <Pattern2>]
      [<left <cons $x $y>>    <Pattern3 x y>]
      [<right <cons ,1 _>>    <Pattern4>]
      [<right <cons ,999 $x>> <Pattern5 x>]
      ;;[<right <nothing>>      <Pattern6>] ;;Error
      [<right <cons $x $y>>   <Pattern7 x y>]})))

(test (my-func <Left <Just 5>>))
(test (my-func <Left <Nothing>>))
;;(test (my-func <Left {1 2 3}>)) ;;Error
(test (my-func <Right {1 2 3 4}>))
(test (my-func <Right {999 2 3 4}>))
;;(test (my-func <Right <Nothing>>))
(test (my-func <Right {2 4 6 8}>))