Add reject (partial function) method to MonadError
#2194
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Oh hang on tests still need attention. I will revisit this after I have fixed them. |
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Thanks for this. The method seems useful, but I do agree that |
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Thanks for taking a look. I've renamed it to Re: binary compatibility, mea cupla, I forgot adding a method to a trait isn't safe prior to Scala 2.12. |
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| @@ -16,6 +16,9 @@ final class MonadErrorOps[F[_], E, A](val fa: F[A]) extends AnyVal { | |||
| def ensureOr(error: A => E)(predicate: A => Boolean)(implicit F: MonadError[F, E]): F[A] = | |||
| F.ensureOr(fa)(error)(predicate) | |||
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| def reject(pf: PartialFunction[A, E])(implicit F: MonadError[F, E]): F[A] = | |||
| F.flatMap(fa)(a => if (pf.isDefinedAt(a)) F.raiseError(pf(a)) else F.pure(a)) | |||
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There is this trick that avoids calling isDefinedAt and then apply of the PartialFunction, maybe worthwhile to copy here, just a thought. Also, instead of F.pure(a) shall we just return fa?
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I'm thinking of doing F.flatMap(fa)(a => pf.andThen(F.raiseError[A]).applyOrElse(a, _ => fa)), though that does create a new "AndThen" object. Is avoiding the allocation important?
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that might be a good balance between readability and performance.
wogan
changed the title
reject (partial function) method to MonadError
Partial functions are a convenient method for expressing
ensure.In ApplicativeError
handleErrorhas another methodrecoverwhich acceptsPartialFunction. This is similar but for the reverse direction. If you can think of a better name thanensurePI'm open to it - perhapsreject,guardorguarantee.