Either matcher of Egison

either_matcher.egi

(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 "------------")
(test (assert-equal "right case : wildcard"
  (match <Right 5> (either string integer) {[<right _> [<OK>]] [_ <KO>]})
  <OK>
))

(test (assert-equal "right case : wildcard / with <left _>, not match"
  (match <Right 5> (either string integer) {[<left _> [<OK>]] [_ <KO>]})
  <KO>
))

(test (assert-equal "right case : return value"
  (match <Right 5> (either string integer) {[<right $x> [x]] [_ <KO>]})
  5
))

(test (assert-equal "left case : return message"
  (match <Left "somethin lefty"> (either string integer) {[<left $x> [x]] [_ <KO>]})
  "somethin lefty"
))

(test (assert-equal "left case : with <right $x>, not match"
  (match <Left "somethin lefty"> (either string integer) {[<right $x> [x]] [_ <KO>]})
  <KO>
))

(test (assert-equal "But, the type params is not useless."
  (match <Left "somethin lefty"> (either float float) {[<left $x> [x]] [_ <KO>]})
  <KO>
))