refactor executor interface

Sources/_StringProcessing/Algorithms/Matching/Matches.swift

@@ -76,11 +76,12 @@ extension RegexMatchesSequence: Sequence {
       guard let position = currentPosition, position <= base.searchBounds.upperBound else {
         return nil
       }
-      
+
       // Otherwise, find the next match (if any) and compute `nextStart`
-      let match = try? base.regex._firstMatch(
+      let match = try? Executor<Output>.firstMatch(
+        base.regex.program.loweredProgram,
         base.input,
-        subjectBounds: base.subjectBounds,
+        subjectBounds: base.subjectBounds, 
         searchBounds: position..<base.searchBounds.upperBound)
       currentPosition = match.flatMap(base.searchIndex(after:))
       return match
@@ -116,6 +117,9 @@ extension BidirectionalCollection where SubSequence == Substring {
     // FIXME: Array init calls count, which double-executes the regex :-(
     // FIXME: just return some Collection<Regex<Output>.Match>
     var result = Array<Regex<Output>.Match>()
+
+
+
     for match in _matches(of: r) {
       result.append(match)
     }

Sources/_StringProcessing/CMakeLists.txt

@@ -18,7 +18,6 @@ add_library(_StringProcessing
   Algorithms/Searchers/CollectionSearcher.swift
   Algorithms/Searchers/ZSearcher.swift
   Engine/Backtracking.swift
-  Engine/Consume.swift
   Engine/InstPayload.swift
   Engine/Instruction.swift
   Engine/MEBuilder.swift

Sources/_StringProcessing/Compiler.swift

@@ -89,7 +89,7 @@ func _compileRegex(
   _ regex: String,
   _ syntax: SyntaxOptions = .traditional,
   _ semanticLevel: RegexSemanticLevel? = nil
-) throws -> Executor {
+) throws -> MEProgram {
   let ast = try parse(regex, syntax)
   let dsl: DSLTree
 
@@ -104,7 +104,7 @@ func _compileRegex(
     dsl = ast.dslTree
   }
   let program = try Compiler(tree: dsl).emit()
-  return Executor(program: program)
+  return program
 }
 
 @_spi(RegexBenchmark)

Sources/_StringProcessing/Engine/Processor.swift

@@ -105,9 +105,7 @@ extension Processor {
     input: Input,
     subjectBounds: Range<Position>,
     searchBounds: Range<Position>,
-    matchMode: MatchMode,
-    isTracingEnabled: Bool,
-    shouldMeasureMetrics: Bool
+    matchMode: MatchMode
   ) {
     self.controller = Controller(pc: 0)
     self.instructions = program.instructions
@@ -117,8 +115,8 @@ extension Processor {
     self.matchMode = matchMode
 
     self.metrics = ProcessorMetrics(
-      isTracingEnabled: isTracingEnabled,
-      shouldMeasureMetrics: shouldMeasureMetrics)
+      isTracingEnabled: program.enableTracing,
+      shouldMeasureMetrics: program.enableTracing)
 
     self.currentPosition = searchBounds.lowerBound
 
@@ -155,12 +153,11 @@ extension Processor {
     _checkInvariants()
   }
 
-  func isReset(
-    currentPosition: Position, searchBounds: Range<Position>
-  ) -> Bool {
-    guard self.currentPosition == currentPosition,
-          self.searchBounds == searchBounds,
-          self.controller == Controller(pc: 0),
+  // Check that resettable state has been reset. Note that `reset()`
+  // takes a new current position and search bounds.
+  func isReset() -> Bool {
+    _checkInvariants()
+    guard self.controller == Controller(pc: 0),
           self.savePoints.isEmpty,
           self.callStack.isEmpty,
           self.storedCaptures.allSatisfy({ $0.range == nil }),