「【翻訳】関数型プログラミング入門 | POSTD」の「パイプラインを使う」をSwiftで書いてみた。

description.md

【翻訳】関数型プログラミング入門 | POSTD の「パイプラインを使う」をSwiftで書いてみた。

pipeline.swift

import Foundation

typealias Band = [String:String]

func assoc(var d: Band, key: String, value: String?) -> Band {
    d[key] = value
    return d
}

typealias FuncForBand = Band -> Band

func pipeline_each(bands: [Band], fns: [FuncForBand]) -> [Band] {
    return reduce(fns, bands, map)
}

typealias StringConverter = String -> String

func call(key: String, fn: StringConverter)(band: Band) -> Band {
    if let value = band[key] {
        return assoc(band, key, fn(value))
    } else {
        return band
    }
}

func pluck(keys: [String])(band: Band) -> Band {
    return reduce(keys, Band()) {
        assoc($0, $1, band[$1])
    }
}

// FuncForBand
let strip_punctuation_from_name = call("name") { $0.stringByReplacingOccurrencesOfString(".", withString: "") }
let capitalize_names = call("name") { $0.capitalizedString }
let set_canada_as_country = call("country", {_ in return "Canada"})
let extract_name_and_country = pluck(["name", "country"])

// pipeline
var bands: [Band] = [
    ["name": "sunset rubdown", "country": "UK", "active": "false"],
    ["name": "women", "country": "Germany", "active": "false"],
    ["name": "a silver mt. zion", "country": "Spain", "active": "true"]
]

pipeline_each(bands, [
    set_canada_as_country,
    strip_punctuation_from_name,
    capitalize_names,
    extract_name_and_country,
    ])

call()とpluck()をCurried Functionに書き直した。