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• Why Polymorphic Variants (For Ok and Error)

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Implementation Notes

Why Polymorphic Variants (For Ok and Error)

Using

type ('a, 'b) t =
  | Ok of 'a
  | Error of 'b

gives two annoying alternatives:

• be incompatible with Core Result.t, or
• depend on Core.

Type equality constraints do not work twice. I.e. one cannot write:

type ('a, 'b) result_core = ('a, 'b) Result.t  = Ok of 'a | Error of 'b
type ('a, 'b) result_err = ('a, 'b) Err.t  = Ok of 'a | Error of 'b
type ('a, 'b) result = ('a, 'b) result_err  = ('a, 'b) result_core

or any combination like that.