generated at
2/18/2025, 4:16:28 PM
QuantifiedConstraints
https://the.igreque.info/slides/2018-12-07-ghc8x.html#(1)
インスタンスの定義に量化が使える
https://downloads.haskell.org/~ghc/8.6.1/docs/html/users_guide/glasgow_exts.html#extension-QuantifiedConstraints