From 738d589008a1ecf647e1d65c8b6b08fe5efdfa3d Mon Sep 17 00:00:00 2001
From: Stephen Celis <stephen@stephencelis.com>
Date: Mon, 1 Jul 2019 09:05:43 -0400
Subject: [PATCH] 63

---
 .../Contents.swift                            | 444 ++++++++++++++++++
 .../contents.xcplayground                     |   4 +
 0063-parser-combinators-pt2/README.md         |   5 +
 README.md                                     |   2 +
 4 files changed, 455 insertions(+)
 create mode 100644 0063-parser-combinators-pt2/ParserCombinators.playground/Contents.swift
 create mode 100644 0063-parser-combinators-pt2/ParserCombinators.playground/contents.xcplayground
 create mode 100644 0063-parser-combinators-pt2/README.md

diff --git a/0063-parser-combinators-pt2/ParserCombinators.playground/Contents.swift b/0063-parser-combinators-pt2/ParserCombinators.playground/Contents.swift
new file mode 100644
index 00000000..9f474377
--- /dev/null
+++ b/0063-parser-combinators-pt2/ParserCombinators.playground/Contents.swift
@@ -0,0 +1,444 @@
+
+struct Parser<A> {
+  let run: (inout Substring) -> A?
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+let int = Parser<Int> { str in
+  let prefix = str.prefix(while: { $0.isNumber })
+  let match = Int(prefix)
+  str.removeFirst(prefix.count)
+  return match
+}
+
+let double = Parser<Double> { str in
+  let prefix = str.prefix(while: { $0.isNumber || $0 == "." })
+  let match = Double(prefix)
+  str.removeFirst(prefix.count)
+  return match
+}
+
+let char = Parser<Character> { str in
+  guard !str.isEmpty else { return nil }
+  return str.removeFirst()
+}
+
+func literal(_ p: String) -> Parser<Void> {
+  return Parser<Void> { str in
+    guard str.hasPrefix(p) else { return nil }
+    str.removeFirst(p.count)
+    return ()
+  }
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+func always<A>(_ a: A) -> Parser<A> {
+  return Parser<A> { _ in a }
+}
+
+extension Parser {
+  static var never: Parser {
+    return Parser { _ in nil }
+  }
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+extension Parser {
+  func map<B>(_ f: @escaping (A) -> B) -> Parser<B> {
+    return Parser<B> { str -> B? in
+      self.run(&str).map(f)
+    }
+  }
+
+  func flatMap<B>(_ f: @escaping (A) -> Parser<B>) -> Parser<B> {
+    return Parser<B> { str -> B? in
+      let original = str
+      let matchA = self.run(&str)
+      let parserB = matchA.map(f)
+      guard let matchB = parserB?.run(&str) else {
+        str = original
+        return nil
+      }
+      return matchB
+    }
+  }
+}
+
+func zip<A, B>(_ a: Parser<A>, _ b: Parser<B>) -> Parser<(A, B)> {
+  return Parser<(A, B)> { str -> (A, B)? in
+    let original = str
+    guard let matchA = a.run(&str) else { return nil }
+    guard let matchB = b.run(&str) else {
+      str = original
+      return nil
+    }
+    return (matchA, matchB)
+  }
+}
+
+
+
+
+
+func zip<A, B, C>(
+  _ a: Parser<A>,
+  _ b: Parser<B>,
+  _ c: Parser<C>
+  ) -> Parser<(A, B, C)> {
+  return zip(a, zip(b, c))
+    .map { a, bc in (a, bc.0, bc.1) }
+}
+func zip<A, B, C, D>(
+  _ a: Parser<A>,
+  _ b: Parser<B>,
+  _ c: Parser<C>,
+  _ d: Parser<D>
+  ) -> Parser<(A, B, C, D)> {
+  return zip(a, zip(b, c, d))
+    .map { a, bcd in (a, bcd.0, bcd.1, bcd.2) }
+}
+func zip<A, B, C, D, E>(
+  _ a: Parser<A>,
+  _ b: Parser<B>,
+  _ c: Parser<C>,
+  _ d: Parser<D>,
+  _ e: Parser<E>
+  ) -> Parser<(A, B, C, D, E)> {
+
+  return zip(a, zip(b, c, d, e))
+    .map { a, bcde in (a, bcde.0, bcde.1, bcde.2, bcde.3) }
+}
+func zip<A, B, C, D, E, F>(
+  _ a: Parser<A>,
+  _ b: Parser<B>,
+  _ c: Parser<C>,
+  _ d: Parser<D>,
+  _ e: Parser<E>,
+  _ f: Parser<F>
+  ) -> Parser<(A, B, C, D, E, F)> {
+  return zip(a, zip(b, c, d, e, f))
+    .map { a, bcdef in (a, bcdef.0, bcdef.1, bcdef.2, bcdef.3, bcdef.4) }
+}
+func zip<A, B, C, D, E, F, G>(
+  _ a: Parser<A>,
+  _ b: Parser<B>,
+  _ c: Parser<C>,
+  _ d: Parser<D>,
+  _ e: Parser<E>,
+  _ f: Parser<F>,
+  _ g: Parser<G>
+  ) -> Parser<(A, B, C, D, E, F, G)> {
+  return zip(a, zip(b, c, d, e, f, g))
+    .map { a, bcdefg in (a, bcdefg.0, bcdefg.1, bcdefg.2, bcdefg.3, bcdefg.4, bcdefg.5) }
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+extension Parser {
+  func run(_ str: String) -> (match: A?, rest: Substring) {
+    var str = str[...]
+    let match = self.run(&str)
+    return (match, str)
+  }
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+// 40.446° N, 79.982° W
+struct Coordinate {
+  let latitude: Double
+  let longitude: Double
+}
+
+func prefix(while p: @escaping (Character) -> Bool) -> Parser<Substring> {
+  return Parser<Substring> { str in
+    let prefix = str.prefix(while: p)
+    str.removeFirst(prefix.count)
+    return prefix
+  }
+}
+
+let zeroOrMoreSpaces = prefix(
+  while: { $0 == " " })
+  .map { _ in () }
+//  Parser<Void> { str -> Void? in
+//  let prefix = str.prefix(while: { $0 == " " })
+//  str.removeFirst(prefix.count)
+//  return ()
+//}
+let oneOrMoreSpaces = prefix(
+  while: { $0 == " " })
+  .flatMap {
+    $0.isEmpty
+      ? .never
+      : always(())
+}
+//  Parser<Void> { str -> Void? in
+//  let prefix = str.prefix(while: { $0 == " " })
+//  guard !prefix.isEmpty else { return nil }
+//  str.removeFirst(prefix.count)
+//  return ()
+//}
+
+
+
+let northSouth = char
+  .flatMap {
+    $0 == "N" ? always(1.0)
+      : $0 == "S" ? always(-1)
+      : .never
+}
+let eastWest = char
+  .flatMap {
+    $0 == "E" ? always(1.0)
+      : $0 == "W" ? always(-1)
+      : .never
+}
+let latitude = zip(
+  double,
+  literal("°"),
+  oneOrMoreSpaces,
+  northSouth
+  )
+  .map { lat, _, _, latSign in lat * latSign }
+let longitude = zip(
+  double,
+  literal("°"),
+  oneOrMoreSpaces,
+  eastWest
+  )
+  .map { long, _, _, longSign in long * longSign }
+let coord = zip(
+  zeroOrMoreSpaces,
+  latitude,
+  literal(","),
+  oneOrMoreSpaces,
+  longitude
+  )
+  .map { _, lat, _, _, long in
+    Coordinate(
+      latitude: lat,
+      longitude: long
+    )
+}
+
+
+
+coord.run("40.446° N, 79.982° W")
+
+
+coord.run("40.446°   N,   79.982°   W")
+coord.run("40.446°   N,   79.982°   W   ")
+coord.run("   40.446°   N,   79.982°   W   ")
+
+
+import Foundation
+
+let df = DateFormatter()
+df.dateStyle = .medium
+
+df.date(from: "Jan 29, 2018")
+df.date(from: "Jan   29,   2018")
+df.date(from: "   Jan   29,   2018")
+
+
+
+try NSRegularExpression(pattern: " *")
+
+
+
+Scanner().charactersToBeSkipped = .whitespaces
+
+
+
+oneOrMoreSpaces.run("   Hello, world!")
+oneOrMoreSpaces.run("Hello, world!")
+
+
+
+"€42,£42,$42"
+
+
+enum Currency { case eur, gbp, usd }
+let currency = char.flatMap {
+  $0 == "€" ? always(Currency.eur)
+    : $0 == "£" ? always(.gbp)
+    : $0 == "$" ? always(.usd)
+    : .never
+}
+
+
+struct Money {
+  let currency: Currency
+  let value: Double
+}
+let money = zip(currency, double).map(Money.init)
+
+
+money.run("€42,£42,$42")
+
+
+zip(money, literal(","), money, literal(","), money)
+  .run("€42,£42")
+
+
+func zeroOrMore<A>(
+  _ p: Parser<A>,
+  separatedBy s: Parser<Void>
+  ) -> Parser<[A]> {
+  return Parser<[A]> { str in
+    var rest = str
+    var matches: [A] = []
+    while let match = p.run(&str) {
+      rest = str
+      matches.append(match)
+      if s.run(&str) == nil {
+        return matches
+      }
+    }
+    str = rest
+    return matches
+  }
+}
+
+
+zeroOrMore(money, separatedBy: literal(","))
+  .run("€42,£42,$42,")
+  .match
+zeroOrMore(money, separatedBy: literal(","))
+  .run("€42,£42,$42,")
+  .rest
+
+
+zeroOrMore(money, separatedBy: literal(""))
+  .run("€42£42$42")
+  .match
+
+let commaOrNewline = char
+  .flatMap { $0 == "," || $0 == "\n" ? always(()) : .never }
+
+dump(
+zeroOrMore(money, separatedBy: commaOrNewline)
+  .run("""
+€42,£42,$42
+€42,£42,$42
+€42,£42,$42,฿10
+""")
+  .match)
+
+zeroOrMore(money, separatedBy: commaOrNewline)
+  .run("""
+€42,£42,$42
+€42,£42,$42
+€42,£42,$42,฿10
+""")
+  .rest
+
+dump(
+  zeroOrMore(money, separatedBy: commaOrNewline)
+    .run("""
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+€42,£42,$42,€42,£42,$42,€42,£42,$42,€42,£42,$42
+""")
+    .match)
diff --git a/0063-parser-combinators-pt2/ParserCombinators.playground/contents.xcplayground b/0063-parser-combinators-pt2/ParserCombinators.playground/contents.xcplayground
new file mode 100644
index 00000000..63b6dd8d
--- /dev/null
+++ b/0063-parser-combinators-pt2/ParserCombinators.playground/contents.xcplayground
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>
\ No newline at end of file
diff --git a/0063-parser-combinators-pt2/README.md b/0063-parser-combinators-pt2/README.md
new file mode 100644
index 00000000..f36a8474
--- /dev/null
+++ b/0063-parser-combinators-pt2/README.md
@@ -0,0 +1,5 @@
+## [Point-Free](https://www.pointfree.co)
+
+> #### This directory contains code from Point-Free Episode: [Parser Combinators: Part 2](https://www.pointfree.co/episodes/ep63-parser-combinators-pt2)
+>
+> Let’s solve another common parsing problem using parser combinators! It’s common to want to parse multiple values off a string, and while `zip` gets us part of the way there, it doesn’t let us part _any_ number of values! Luckily there’s a parser combinator that can help, and it really packs a punch.
diff --git a/README.md b/README.md
index a403d93b..8eda73f7 100644
--- a/README.md
+++ b/README.md
@@ -64,3 +64,5 @@ This repository is the home of code written on episodes of
 1. [Composable Parsing: Map](0059-composable-parsing-map)
 1. [Composable Parsing: Flat-Map](0060-composable-parsing-flat-map)
 1. [Composable Parsing: Zip](0061-composable-parsing-zip)
+1. [Parser Combinators: Part 1](0062-parser-combinators-pt1)
+1. [Parser Combinators: Part 2](0063-parser-combinators-pt2)