Infix operators for monadic functions in Swift
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Latest commit 30701f9 Apr 15, 2018

Indecipherable symbols that some people claim have actual meaning.

pod Carthage compatible Swift Package Manager compatible

Please see the documentation for version compatibility and installation information.

What's included?

Importing Runes introduces several new operators and one global function that correspond to common Haskell typeclasses:


  • <^> (pronounced "map")

Applicative Functor

  • <*> (pronounced "apply")
  • <* (pronounced "left sequence")
  • *> (pronounced "right sequence")
  • pure (pronounced "pure")


  • <|> (pronounced "alternate")
  • empty (pronounced "empty")


  • >>- (pronounced "flatMap") (left associative)
  • -<< (pronounced "flatMap") (right associative)
  • >-> (pronounced "Monadic compose") (left associative)
  • <-< (pronounced "Monadic compose") (right associative)


We also include default implementations for Optional and Array with the following type signatures:

// Optional+Functor:
public func <^> <T, U>(f: T -> U, x: T?) -> U?

// Optional+Applicative:
public func <*> <T, U>(f: (T -> U)?, x: T?) -> U?
public func <* <T, U>(lhs: T?, rhs: U?) -> T?
public func *> <T, U>(lhs: T?, rhs: U?) -> U?
public func pure<T>(x: T) -> T?

// Optional+Alternative:
public func <|> <T>(lhs: T?, rhs: T?) -> T?
public func empty<T>() -> T?

// Optional+Monad:
public func >>- <T, U>(x: T?, f: T -> U?) -> U?
public func -<< <T, U>(f: T -> U?, x: T?) -> U?
public func >-> <T, U, V>(f: T -> U?, g: U -> V?) -> T -> V?
public func <-< <T, U, V>(f: U -> V?, g: T -> U?) -> T -> V?

// Array+Functor:
public func <^> <T, U>(f: T -> U, x: [T]) -> [U]

// Array+Applicative:
public func <*> <T, U>(fs: [T -> U], x: [T]) -> [U]
public func <* <T, U>(lhs: [T], rhs: [U]) -> [T]
public func *> <T, U>(lhs: [T], rhs: [U]) -> [U]
public func pure<T>(x: T) -> [T]

// Array+Alternative:
public func <|> <T>(lhs: [T], rhs: [T]) -> [T]
public func empty<T>() -> [T]

// Array+Monad:
public func >>- <T, U>(x: [T], f: T -> [U]) -> [U]
public func -<< <T, U>(f: T -> [U], x: [T]) -> [U]
public func >-> <T, U, V>(f: T -> [U], g: U -> [V]) -> T -> [V]
public func <-< <T, U, V>(f: U -> [V], g: T -> [U]) -> T -> [V]


See the CONTRIBUTING document. Thank you, contributors!


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