Add 'submodules/SSignalKit/' from commit '359b2ee7c9f20f99f221f78e307369ef5ad0ece2'

git-subtree-dir: submodules/SSignalKit
git-subtree-mainline: 4459dc5b47
git-subtree-split: 359b2ee7c9

submodules/SSignalKit/SwiftSignalKit/Signal_Loop.swift

@@ -0,0 +1,46 @@
+import Foundation
+
+public enum SignalFeedbackLoopState<T> {
+    case initial
+    case loop(T)
+}
+
+public func feedbackLoop<R1, R, E>(once: @escaping (SignalFeedbackLoopState<R1>) -> Signal<R1, E>?, reduce: @escaping (R1, R1) -> R1) -> Signal<R, E> {
+    return Signal { subscriber in
+        let currentDisposable = MetaDisposable()
+        
+        let state = Atomic<R1?>(value: nil)
+        
+        var loopAgain: (() -> Void)?
+        
+        let loopOnce: (MetaDisposable?) -> Void = { disposable in
+            if let signal = once(.initial) {
+                disposable?.set(signal.start(next: { next in
+                    let _ = state.modify { value in
+                        if let value = value {
+                            return reduce(value, next)
+                        } else {
+                            return value
+                        }
+                    }
+                }, error: { error in
+                    subscriber.putError(error)
+                }, completed: {
+                    loopAgain?()
+                }))
+            } else {
+                subscriber.putCompletion()
+            }
+        }
+        
+        loopAgain = { [weak currentDisposable] in
+            loopOnce(currentDisposable)
+        }
+        
+        loopOnce(currentDisposable)
+        
+        return ActionDisposable {
+            currentDisposable.dispose()
+        }
+    }
+}