feat: Coleman-Liau Index.

Sources/Readability/CommonMetrics.swift

@@ -12,6 +12,7 @@ public enum RACommonMetric {
   case sentenceCount
   case wordCount
   case syllableCount
+  case characterCount
   case avgWordsPerSentence
   case avgSyllablesPerWord
 }
@@ -21,6 +22,8 @@ public struct RACommonMetricsCalculator {
 
   private var metrics: Set<RACommonMetric>
 
+  private static let excludeCharacters: [Character] = ["-", "'"]
+
   public init(metrics: Set<RACommonMetric>) {
     self.metrics = metrics
   }
@@ -34,11 +37,14 @@ public struct RACommonMetricsCalculator {
     let shouldDoWords = metrics.contains(.wordCount)
       || metrics.contains(.avgWordsPerSentence)
       || metrics.contains(.avgSyllablesPerWord)
+      || metrics.contains(.characterCount)
     let shouldCountSyllables = metrics.contains(.avgSyllablesPerWord) || metrics.contains(.syllableCount)
+    let shouldCountCharacters = metrics.contains(.characterCount)
 
     var sentenceCount = 0
     var wordCount = 0
     var syllableCount = 0
+    var characterCount = 0
 
     if shouldDoSentences {
       sentenceCount = RATokenizer(text, unit: .sentence).enumerateTokens { _ in }
@@ -46,12 +52,15 @@ public struct RACommonMetricsCalculator {
 
     if shouldDoWords {
       let tokenizer = RATokenizer(text, unit: .word)
-      if shouldCountSyllables {
       wordCount = tokenizer.enumerateTokens { word in
+        if shouldCountSyllables {
           syllableCount += countSyllables(word: word)
         }
-      } else {
-        wordCount = tokenizer.enumerateTokens { _ in }
+        if shouldCountCharacters {
+          characterCount += word
+            .filter { !Self.excludeCharacters.contains($0) }
+            .count
+        }
       }
     }
 
@@ -62,6 +71,7 @@ public struct RACommonMetricsCalculator {
       case .syllableCount: value = Double(syllableCount)
       case .sentenceCount: value = Double(sentenceCount)
       case .wordCount: value = Double(wordCount)
+      case .characterCount: value = Double(characterCount)
       case .avgWordsPerSentence: value = Double(wordCount) / Double(sentenceCount)
       case .avgSyllablesPerWord: value = Double(syllableCount) / Double(wordCount)
       }

Sources/Readability/Scorers/ColemanLiauIndex.swift

@@ -0,0 +1,34 @@
+//
+//  File.swift
+//  
+//
+//  Created by Shibo Lyu on 2022/5/20.
+//
+
+import Foundation
+
+public struct RAColemanLiauIndexScorer: RAScorer {
+  public static let requiresCommonMetrics: Set<RACommonMetric>? = [
+    .wordCount,
+    .characterCount,
+    .sentenceCount
+  ]
+
+  public static let meta = RAScorerMeta(
+    name: "Coleman–Liau Index",
+    creator: "Meri Coleman & T. L. Liau",
+    citation: "Coleman, M., & Liau, T. L. (1975). A computer readability formula designed for machine scoring. Journal of Applied Psychology, 60(2), 283."
+  )
+
+  public init() {}
+
+  public func score(_ text: String, metrics: RACommonMetricsCalculator.Results?) -> Double {
+    let wordCount = metrics![.wordCount]!
+
+    let l = metrics![.characterCount]! * 100 / wordCount
+    let s = metrics![.sentenceCount]! * 100 / wordCount
+
+    let cloze = 141.8401 - (0.214590 * l) + (1.079812 * s)
+    return (-27.4004 * cloze) + 23.06395
+  }
+}

Sources/Readability/ScoringTask.swift

@@ -13,11 +13,13 @@ public class RAScoringTask {
   public enum Scorer: Hashable, CaseIterable, Comparable {
     case fleschReadingEase
     case fleschKincaidGrade
+    case colemanLiauIndex
   }
 
   public static let availableScorers: [Scorer: RAScorer.Type] = [
     .fleschReadingEase: RAFleschReadingEaseScorer.self,
-    .fleschKincaidGrade: RAFleschKincaidGradeScorer.self
+    .fleschKincaidGrade: RAFleschKincaidGradeScorer.self,
+    .colemanLiauIndex: RAColemanLiauIndexScorer.self
   ]
 
   public var scorersToRun: Set<Scorer>