| import java.time.ZoneId | |
| import java.time.format.DateTimeFormatterBuilder | |
| import java.time.temporal.TemporalQueries | |
| def parseZoneId(input: String): ZoneId = | |
| new DateTimeFormatterBuilder() | |
| .appendZoneId | |
| .toFormatter | |
| .parse(input) | |
| .query(TemporalQueries.zoneId) |
| def foldMapF[F[_]: Monad, A, B](o: OptionT[F, A], f: A => B)(implicit M0: Monoid[B]): F[B] = o.fold(f, M0.zero) |
| trait HasInverse[A] | |
| object HasInverse { | |
| def apply[A]: HasInverse[A] = new HasInverse[A] {} | |
| } | |
| implicit def dummyHasInverse[A]: HasInverse[A] = HasInverse[A] | |
| trait Inverse[A, B] { self => | |
| def value: A | |
| def inverse: B |
| object jsonExample { | |
| import scala.language.higherKinds | |
| import scalaz._, Scalaz._ | |
| type Path = String | |
| type JValue | |
| type JObject | |
| implicit class RichDisjunction[A, B](disjunction: A \/ B) { |
Say we have a morally correct json library.
It comes with types like: JValue, JObject and Path.
It also has error types extending JsonError like ParsingError, CastingError and FieldError. To make it even smarter, there's a sweet Semigroup[JsonError] to accumulate errors properly (left as an exercise).
Finally, there are a bunch of basic combinators:
def parse(in: String): ParsingError \/ JValue
| def retry[F[_]: Monad, E, A](f: => EitherT[F, E, A])(n: Int): EitherT[F, List[E], A] = | |
| Stream.fill(n)(f).traverseU(_.swap).map(_.toList).swap |
| « Mais c'est précisément parce que j'attends peu de chose de la condition humaine, les périodes de bonheur, les progrès partiels, les efforts de recommencement et de continuité me semblent autant de prodiges qui compensent presque l'immense masse des maux, des échecs, de l'incurie et de l'erreur. Les catastrophes et les ruines viendront ; le désordre triomphera, mais de temps en temps l'ordre aussi. La paix s'installera de nouveau entre deux périodes de guerre ; les mots de liberté, d'humanité, de justice retrouveront çà et là le sens que nous avons tenté de leur donner. » | |
| – Marguerite Yourcenar, « Mémoires d'Hadrien » |
| import Data.Tuple | |
| {-- | |
| Okay, shoot! Fell asleep while composing a problem; sorry for the delay! | |
| So, this one is an easy one. We get a little Forth'y'. This is from P19 | |
| of the P99 problem-set. | |
| --} |
| {-| Keep equal elements that are at the same position in both lists | |
| Examples: | |
| >>> keepEqual "hello" "world" | |
| "l" | |
| >>> keepEqual (repeat 1) [0..10] | |
| [1] |
| {-# LANGUAGE TupleSections #-} | |
| -- Follow the type and the properties | |
| f :: Either a a -> (Bool, a) | |
| f = either (False,) (True,) | |
| g :: (Bool, a) -> Either a a | |
| g (False, a) = Left a | |
| g (True, a) = Right a |