Swift Functional Programming - Second Edition

<|? operator

The <|? operator is used to decode an optional value at the specified key path into the requested type:

public func <|? <A: Decodable>(json: JSON, keys: [String]) -> Decoded<A?> where A == A.DecodedType {   switch flatReduce(keys, initial: json, combine: decodedJSON) {   case .failure: return .success(.none)   case .success(let x): return A.decode(x) >>- {           .success(.some($0)) }   } }