@_functionBuilder support for Pipeline.

BuildPipeline.swift

// MARK: FunctionBuilder
@_functionBuilder
struct BuildPipeline {

    static func buildBlock<A>(_ a: A) -> Pipeline<A.Input, A.Output>
        where
        A: Job
    {
        Pipeline(description: descriptionOf(jobs: [a])) { input in
            try a.work(input: input)
        }
    }

    static func buildBlock<A, B>(_ a: A, _ b: B) -> Pipeline<A.Input, B.Output>
        where
        A: Job, B: Job,
        A.Output == B.Input
    {
        Pipeline(description: descriptionOf(jobs: [a, b])) {
            try $0 |> a |> b
        }
    }

    static func buildBlock<A, B, C>(_ a: A, _ b: B, _ c: C) -> Pipeline<A.Input, C.Output>
        where
        A: Job, B: Job, C: Job,
        A.Output == B.Input,
        B.Output == C.Input
    {
        Pipeline(description: descriptionOf(jobs: [a, b, c])) {
            try $0 |> a |> b |> c
        }
    }

    static func buildBlock<A, B, C, D>(_ a: A, _ b: B, _ c: C, _ d: D) -> Pipeline<A.Input, D.Output>
        where
        A: Job, B: Job, C: Job, D: Job,
        A.Output == B.Input,
        B.Output == C.Input,
        C.Output == D.Input
    {
        Pipeline(description: descriptionOf(jobs: [a, b, c, d])) {
            try $0 |> a |> b |> c |> d
        }
    }
    
    // etc... all the way up to 10 different jobs...
}