Add episode 33

0033-protocol-witnesses-pt1/README.md

@@ -0,0 +1,5 @@
+## [Point-Free](https://www.pointfree.co)
+
+> #### This directory contains code from Point-Free Episode: [Protocol Witnesses: Part 1](https://www.pointfree.co/episodes/ep33-protocol-witnesses-part-1)
+>
+> Protocols are a great tool for abstraction, but aren’t the only one. This week we begin to explore the tradeoffs of using protocols by highlighting a few areas in which they fall short in order to demonstrate how we can recover from these problems using a different tool and different tradeoffs.

0033-protocol-witnesses-pt1/Witness.xcworkspace/xcshareddata/IDEWorkspaceChecks.plist

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>IDEDidComputeMac32BitWarning</key>
+	<true/>
+</dict>
+</plist>

0033-protocol-witnesses-pt1/Witnesses.playground/Contents.swift

@@ -0,0 +1,155 @@
+
+protocol Describable {
+  var describe: String { get }
+}
+
+struct PostgresConnInfo {
+  var database: String
+  var hostname: String
+  var password: String
+  var port: Int
+  var user: String
+}
+
+let localhostPostgres = PostgresConnInfo(
+  database: "pointfreeco_development",
+  hostname: "localhost",
+  password: "",
+  port: 5432,
+  user: "pointfreeco"
+)
+
+//extension PostgresConnInfo: Describable {
+//  var describe: String {
+//    return "PostgresConnInfo(database: \"\(self.database)\", hostname: \"\(self.hostname)\", password: \"\(self.password)\", port: \"\(self.port)\", user: \"\(self.user)\")"
+//  }
+//}
+
+//extension PostgresConnInfo: Describable {
+//  var describe: String {
+//    return """
+//PostgresConnInfo(
+//  database: \"\(self.database)\",
+//  hostname: \"\(self.hostname)\",
+//  password: \"\(self.password)\",
+//  port: \"\(self.port)\",
+//  user: \"\(self.user)\"
+//)
+//"""
+//  }
+//}
+
+extension PostgresConnInfo: Describable {
+  var describe: String {
+    return "postgres://\(self.user):\(self.password)@\(self.hostname):\(self.port)/\(self.database)"
+  }
+}
+
+print(localhostPostgres.describe)
+
+extension Int: Describable {
+  var describe: String {
+    return "\(self)"
+  }
+}
+
+2.describe
+
+protocol EmptyInitializable {
+  init()
+}
+
+extension String: EmptyInitializable {
+}
+extension Array: EmptyInitializable {
+}
+extension Int: EmptyInitializable {
+  init() {
+    self = 1
+  }
+}
+extension Optional: EmptyInitializable {
+  init() {
+    self = nil
+  }
+}
+
+[1, 2, 3].reduce(0, +)
+
+extension Array {
+  func reduce<Result: EmptyInitializable>(_ accumulation: (Result, Element) -> Result) -> Result {
+    return self.reduce(Result(), accumulation)
+  }
+}
+
+[1, 2, 3].reduce(+)
+[[1, 2], [], [3, 4]].reduce(+)
+["Hello", " ", "Blob"].reduce(+)
+
+protocol Combinable {
+  func combine(with other: Self) -> Self
+}
+
+struct Combining<A> {
+  let combine: (A, A) -> A
+}
+
+extension Int: Combinable {
+  func combine(with other: Int) -> Int {
+    return self * other
+  }
+}
+extension String: Combinable {
+  func combine(with other: String) -> String {
+    return self + other
+  }
+}
+extension Array: Combinable {
+  func combine(with other: Array) -> Array {
+    return self + other
+  }
+}
+extension Optional: Combinable {
+  func combine(with other: Optional) -> Optional {
+    return self ?? other
+  }
+}
+
+extension Array where Element: Combinable {
+  func reduce(_ initial: Element) -> Element {
+    return self.reduce(initial) { $0.combine(with: $1) }
+  }
+}
+
+extension Array /* where Element: Combinable */ {
+  func reduce(_ initial: Element, _ combining: Combining<Element>) -> Element {
+    return self.reduce(initial, combining.combine)
+  }
+}
+
+[1, 2, 3].reduce(1)
+[[1, 2], [], [3, 4]].reduce([])
+[nil, nil, 3].reduce(nil)
+
+let sum = Combining<Int>(combine: +)
+[1, 2, 3, 4].reduce(0, sum)
+
+let product = Combining<Int>(combine: *)
+[1, 2, 3, 4].reduce(1, product)
+
+
+extension Array where Element: Combinable & EmptyInitializable {
+  func reduce() -> Element {
+    return self.reduce(Element()) { $0.combine(with: $1) }
+  }
+}
+
+[1, 2, 3, 4].reduce()
+[[1, 2], [], [3, 4]].reduce()
+[nil, nil, 3].reduce()
+
+//extension Int: Combinable {
+//  func combine(with other: Int) -> Int {
+//    return self * other
+//  }
+//}

0033-protocol-witnesses-pt1/Witnesses.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

README.md

@@ -33,4 +33,6 @@ This repository is the home of code written on episodes of
 1. [An HTML DSL](0028-html-dsl)
 1. [DSLs vs. Templating Languages](0029-dsls-vs-templating-languages)
 1. [Composable Randomness](0030-composable-randomness)
-1. [Decodable Randomness](0031-arbitrary-pt1)
+1. [Decodable Randomness: Part 1](0031-arbitrary-pt1)
+1. [Decodable Randomness: Part 2](0032-arbitrary-pt2)
+1. [Protocol Witnesses: Part 1](0033-protocol-witnesses-pt1))