[DRAFT] Refactor quant nonmutating

Sources/_StringProcessing/ConsumerInterface.swift

@@ -391,9 +391,8 @@ extension DSLTree.CustomCharacterClass.Member {
 
       return { input, bounds in
         let curIdx = bounds.lowerBound
-        let nextIndex = isCharacterSemantic
-          ? input.index(after: curIdx)
-          : input.unicodeScalars.index(after: curIdx)
+        let nextIndex = input.index(
+          after: curIdx, isScalarSemantics: !isCharacterSemantic)
 
         // Under grapheme semantics, we compare based on single NFC scalars. If
         // such a character is not single scalar under NFC, the match fails. In
@@ -603,9 +602,9 @@ extension AST.Atom.CharacterProperty {
         if p(input, bounds) != nil { return nil }
 
         // TODO: bounds check
-        return opts.semanticLevel == .graphemeCluster
-          ? input.index(after: bounds.lowerBound)
-          : input.unicodeScalars.index(after: bounds.lowerBound)
+        return input.index(
+          after: bounds.lowerBound, 
+          isScalarSemantics: opts.semanticLevel == .unicodeScalar)
       }
     }
 

Sources/_StringProcessing/Engine/MEBuiltins.swift

@@ -223,6 +223,25 @@ extension String {
     else { return nil }
     return next
   }
+
+  internal func matchRegexDot(
+    at currentPosition: Index,
+    limitedBy end: Index,
+    anyMatchesNewline: Bool,
+    isScalarSemantics: Bool
+  ) -> Index? {
+    guard currentPosition < end else { return nil }
+
+    if anyMatchesNewline {
+      return index(
+        after: currentPosition, isScalarSemantics: isScalarSemantics)
+    }
+
+    return matchAnyNonNewline(
+      at: currentPosition,
+      limitedBy: end,
+      isScalarSemantics: isScalarSemantics)
+  }
 }
 
 // MARK: - Built-in character class matching