Issue #30
Haskell is notorious for currying, and Swift has currying, too
I love ReactiveCocoa, RxSwift and I always take time to dig into it. The other day, I was practise making Signal based on this talk UIKonf 2015 - Jens Ravens: Functional Reactive Programming without Black Magic
Take a look at my repo Signal
filter
I was making a filter for a Signal. The idea of filter is that we should update signal if the Event is Next with right filtered value
Signal.swift
public func filter(f: T -> Bool) -> Signal<T>{
let signal = Signal<T>()
subscribe { result in
switch(result) {
case let .Success(value):
if f(value) {
signal.update(result)
}
case let .Error(error): signal.update(.Error(error))
}
}
return signal
}
2 params
But having Event as another monad, I think it should be more encapsulated if that switching logic gets moved into the Event. Here the filter takes 2 params
Event.swift
func filter(f: T -> Bool, callback: (Event<T> -> Void)) {
switch self {
case let .Next(value) where f(value):
callback(self)
case .Failed:
callback(self)
default:
break
}
}
Signal.swift
public func filter(f: T -> Bool) -> Signal<T> {
let signal = Signal<T>()
subscribe { event in
event.filter(f, callback: signal.update)
}
return signal
}
Currying
With currying, we can make filter a more abstract function, and defer the decision to pass the callback param. It is a little carried away but I find it helpful this way
Now filter accepts 1 param, and it returns a function that takes callback as its param
Event.swift
func filter(f: T -> Bool) -> ((Event<T> -> Void) -> Void) {
return { g in
switch self {
case let .Next(value) where f(value):
g(self)
case .Failed:
g(self)
default:
break
}
}
}
Signal.swift
public func filter(f: T -> Bool) -> Signal<T> {
let signal = Signal<T>()
subscribe { event in
event.filter(f)(signal.update)
}
return signal
}
Curry syntax in Swift 2
Swift 2 supports curry syntax function
func sum(a: Int)(b: Int) -> Int {
return a + b
}
let sumWith5 = sum(5)
let result = sumWith5(b: 10)
No more curry syntax in Swift 3
You may want to find out
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