diff --git a/Sources/Common/Execution.swift b/Sources/Common/Execution.swift
index bbf75d7..ea94a4d 100644
--- a/Sources/Common/Execution.swift
+++ b/Sources/Common/Execution.swift
@@ -15,25 +15,32 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
+public typealias StatementInterloper = (EvaluatableStatement, ControlFlow, ProgramExecution) -> Void
+public typealias ExpressionInterloper = (EvaluatableExpression, Result<P4Value>, ProgramExecution) -> Void
+
 open class ProgramExecution: CustomStringConvertible {
   public var scopes: VarValueScopes = VarValueScopes()
-  let initialValues: VarValueScopes?
+  var globalValues: VarValueScopes?
   var error: Error?
   var debug: DebugLevel = DebugLevel.Error
+  var statement_interloper: StatementInterloper?
+  var expression_interloper: ExpressionInterloper?
 
   init(copy: ProgramExecution) {
     self.scopes = copy.scopes
-    self.initialValues = copy.initialValues
+    self.globalValues = copy.globalValues
     self.error = copy.error
     self.debug = copy.debug
+    self.statement_interloper = copy.statement_interloper
+    self.expression_interloper = copy.expression_interloper
   }
 
   public init() {
-    initialValues = .none
+    globalValues = .none
   }
 
   public init(withGlobalValues values: VarValueScopes) {
-    initialValues = values
+    globalValues = values
   }
 
   open var description: String {
@@ -64,6 +71,26 @@ open class ProgramExecution: CustomStringConvertible {
     return pe
   }
 
+  public func getStatementInterloper() -> StatementInterloper? {
+    return self.statement_interloper
+  }
+
+  public func setStatementInterloper(_ interloper: @escaping StatementInterloper) -> ProgramExecution {
+    let pe = ProgramExecution(copy: self)
+    pe.statement_interloper = interloper
+    return pe
+  }
+
+  public func getExpressionInterloper() -> ExpressionInterloper? {
+    return self.expression_interloper
+  }
+
+  public func setExpressionInterloper(_ interloper: @escaping ExpressionInterloper) -> ProgramExecution {
+    let pe = ProgramExecution(copy: self)
+    pe.expression_interloper = interloper
+    return pe
+  }
+
   open func isDone() -> Bool {
     return false
   }
@@ -101,9 +128,17 @@ open class ProgramExecution: CustomStringConvertible {
     return new_pe
   }
 
-  public func initial_values() -> VarValueScopes? {
-    return self.initialValues
+  public func getGlobalValues() -> VarValueScopes {
+    return self.globalValues ?? VarValueScopes()
   }
+
+  public func setGlobalValues(_ global_values: VarValueScopes) -> ProgramExecution {
+    let new_pe = ProgramExecution(copy: self)
+    new_pe.globalValues = global_values
+    return new_pe
+  }
+
+
 }
 
 /// A scope that resolves variable identifiers to their values.
diff --git a/Sources/Common/Support.swift b/Sources/Common/Support.swift
index 1ef4ae4..ebc62b6 100644
--- a/Sources/Common/Support.swift
+++ b/Sources/Common/Support.swift
@@ -117,24 +117,13 @@ public enum Result<OKT>: Equatable {
   }
 }
 
-extension Result where OKT: CustomStringConvertible {
+extension Result: CustomStringConvertible where OKT: CustomStringConvertible {
   public var description: String {
     switch self {
     case Result.Error(let e):
       return e.msg
     case Result.Ok(let o):
-      return "\(o)"
-    }
-  }
-}
-
-extension Result: CustomStringConvertible {
-  public var description: String {
-    switch self {
-    case Result.Error(let e):
-      return e.msg
-    case Result.Ok(_):
-      return "Ok"
+      return "Ok: \(o)"
     }
   }
 }
diff --git a/Sources/P4Lang/Common.swift b/Sources/P4Lang/Common.swift
index 7500006..3b785c2 100644
--- a/Sources/P4Lang/Common.swift
+++ b/Sources/P4Lang/Common.swift
@@ -90,7 +90,7 @@ public struct ParameterList: CustomStringConvertible, Equatable {
 public struct ArgumentList {
   public let arguments: [Argument]
 
-  public init(_ arguments: [Argument]) {
+  public init(_ arguments: [Argument] = []) {
     self.arguments = arguments
   }
 
diff --git a/Sources/P4Runtime/Common.swift b/Sources/P4Runtime/Common.swift
index 87d0fe5..f6fc9d9 100644
--- a/Sources/P4Runtime/Common.swift
+++ b/Sources/P4Runtime/Common.swift
@@ -32,7 +32,8 @@ public func Call<T>(
   for (parameter, argument) in zip(params.parameters, args.arguments) {
     let arg_idx = argument.index
     let arg_value = argument.argument
-    let maybe_argument_value = arg_value.evaluate(execution: called_execution)
+    //let maybe_argument_value = arg_value.evaluate(execution: called_execution)
+    let maybe_argument_value = EvaluateExpression(arg_value, inExecution: called_execution)
     guard case (.Ok(let argument_value), let updated_execution) = maybe_argument_value else {
       return (
         .Error(Error(withMessage: "Cannot evaluate argument \(arg_idx): \(argument)")),
@@ -82,3 +83,63 @@ public func Call<T>(
   }
   return (.Ok(call_result), updated_execution.replaceScopes(inout_scopes))
 }
+
+public typealias ExecuteStatementResultHandler = (ControlFlow, ProgramExecution) -> (ControlFlow, ProgramExecution)
+
+public func ExecuteStatement(
+  _ statements: [EvaluatableStatement], handleResult handler: ExecuteStatementResultHandler,
+  inExecution execution: ProgramExecution,
+) -> (ControlFlow, ProgramExecution) {
+
+  var debugger: StatementInterloper? = .none
+  var hasDebugInterloper = false
+  if let found_deb = execution.getStatementInterloper() {
+    debugger = found_deb
+    hasDebugInterloper = true
+  }
+
+  var execution = execution
+  for s in statements {
+    let (control_flow, next_execution) = s.evaluate(execution: execution)
+
+    if hasDebugInterloper {
+      debugger!(s, control_flow, next_execution)
+    }
+
+    switch handler(control_flow, next_execution) {
+    case (ControlFlow.Next, let handled_next_execution): execution = handled_next_execution
+    case (ControlFlow.Return(let value), let handled_next_execution):
+      return (ControlFlow.Return(value), handled_next_execution)
+    case (let handled_control_flow, let handled_next_execution):
+      return (handled_control_flow, handled_next_execution)
+    }
+  }
+  return (ControlFlow.Next, execution)
+}
+
+public func ExecuteStatement(
+  _ statement: EvaluatableStatement, handleResult handler: ExecuteStatementResultHandler,
+  inExecution execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
+  return ExecuteStatement([statement], handleResult: handler, inExecution: execution)
+}
+
+public func EvaluateExpression(
+  _ expression: EvaluatableExpression, inExecution execution: ProgramExecution,
+) -> (Result<P4Value>, ProgramExecution) {
+
+  var debugger: ExpressionInterloper? = .none
+  var hasDebugInterloper = false
+  if let found_deb = execution.getExpressionInterloper() {
+    debugger = found_deb
+    hasDebugInterloper = true
+  }
+
+  let (result, execution) = expression.evaluate(execution: execution)
+
+  if hasDebugInterloper {
+    debugger!(expression, result, execution)
+  }
+
+  return (result, execution)
+
+}
diff --git a/Sources/P4Runtime/Expressions.swift b/Sources/P4Runtime/Expressions.swift
index c374a9c..90c5d5d 100644
--- a/Sources/P4Runtime/Expressions.swift
+++ b/Sources/P4Runtime/Expressions.swift
@@ -30,14 +30,14 @@ extension SelectCaseExpression: EvaluatableExpression {
 
 extension SelectExpression: EvaluatableExpression {
   public func evaluate(execution: ProgramExecution) -> (Result<P4Value>, ProgramExecution) {
-    switch self.selector.evaluate(execution: execution) {
+    switch EvaluateExpression(self.selector, inExecution: execution) {
     case (.Ok(let selector_value), let updated_execution):
       for sce in self.case_expressions {
-        if case (.Ok(let kse), let updated_execution) = sce.key.evaluate(
-          execution: updated_execution),
+        if case (.Ok(let kse), let updated_execution) = EvaluateExpression(sce.key, inExecution: updated_execution),
           kse.eq(selector_value)
         {
-          let result = sce.evaluate(execution: updated_execution)
+          //let result = sce.evaluate(execution: updated_execution)
+          let result = EvaluateExpression(sce, inExecution: updated_execution)
           return result
         }
       }
@@ -210,12 +210,14 @@ public func binary_int_math_operator_checker(
 extension BinaryOperatorExpression: EvaluatableExpression {
   public func evaluate(execution: ProgramExecution) -> (Result<P4Value>, ProgramExecution) {
     let updated_execution = execution
-    let maybe_evaluated_left = self.left.evaluate(execution: updated_execution)
+    //let maybe_evaluated_left = self.left.evaluate(execution: updated_execution)
+    let maybe_evaluated_left = EvaluateExpression(self.left, inExecution: updated_execution)
     guard case (.Ok(let evaluated_left), let updated_execution) = maybe_evaluated_left else {
       return maybe_evaluated_left
     }
 
-    let maybe_evaluated_right = self.right.evaluate(execution: updated_execution)
+    //let maybe_evaluated_right = self.right.evaluate(execution: updated_execution)
+    let maybe_evaluated_right = EvaluateExpression(self.right, inExecution: updated_execution)
     guard case (.Ok(let evaluated_right), let updated_execution) = maybe_evaluated_right else {
       return maybe_evaluated_right
     }
@@ -231,12 +233,14 @@ extension BinaryOperatorExpression: EvaluatableExpression {
 extension ArrayAccessExpression: EvaluatableExpression {
   public func evaluate(execution: ProgramExecution) -> (Result<P4Value>, ProgramExecution) {
     let updated_execution = execution
-    let maybe_name = self.name.evaluate(execution: updated_execution)
+    //let maybe_name = self.name.evaluate(execution: updated_execution)
+    let maybe_name = EvaluateExpression(self.name, inExecution: updated_execution)
     guard case (.Ok(let name), let updated_execution) = maybe_name else {
       return maybe_name
     }
 
-    let maybe_indexor = self.indexor.evaluate(execution: updated_execution)
+    //let maybe_indexor = self.indexor.evaluate(execution: updated_execution)
+    let maybe_indexor = EvaluateExpression(self.indexor, inExecution: updated_execution)
     guard case (.Ok(let indexor), let updated_execution) = maybe_indexor else {
       return maybe_indexor
     }
@@ -265,7 +269,8 @@ extension ArrayAccessExpression: EvaluatableLValueExpression {
   ) -> Common.Result<(Common.VarValueScopes, P4Value)> {
 
     let updated_execution = execution
-    let maybe_value = self.name.evaluate(execution: updated_execution)
+    //let maybe_value = self.name.evaluate(execution: updated_execution)
+    let maybe_value = EvaluateExpression(self.name, inExecution: updated_execution)
     guard case (.Ok(let value), let updated_execution) = maybe_value else {
       return .Error(
         Error(withMessage: "\(self.name) cannot be evaluated: \(maybe_value.0.error()!)"))
@@ -275,7 +280,8 @@ extension ArrayAccessExpression: EvaluatableLValueExpression {
     }
 
     // Now, get the indexor!
-    let maybe_indexor_value = self.indexor.evaluate(execution: updated_execution)
+    //let maybe_indexor_value = self.indexor.evaluate(execution: updated_execution)
+    let maybe_indexor_value = EvaluateExpression(self.indexor, inExecution: updated_execution)
     guard case (.Ok(let indexor_value), let updated_execution) = maybe_indexor_value else {
       return Result.Error(
         Error(withMessage: "\(self.indexor) cannot be evaluated: \(maybe_indexor_value.0.error()!)")
@@ -341,7 +347,8 @@ extension FieldAccessExpression: EvaluatableExpression {
   public func evaluate(execution: ProgramExecution) -> (Result<P4Value>, ProgramExecution) {
 
     let updated_execution = execution
-    let maybe_struct = self.strct.evaluate(execution: updated_execution)
+    //let maybe_struct = self.strct.evaluate(execution: updated_execution)
+    let maybe_struct = EvaluateExpression(self.strct, inExecution: updated_execution)
     guard case (.Ok(let strct), let updated_execution) = maybe_struct else {
       return maybe_struct
     }
@@ -375,7 +382,8 @@ extension FieldAccessExpression: EvaluatableLValueExpression {
 
     let updated_execution = execution
     // First, evaluate strct_id and make sure that it names a struct.
-    let maybe_value = self.strct.evaluate(execution: updated_execution)
+    //let maybe_value = self.strct.evaluate(execution: updated_execution)
+    let maybe_value = EvaluateExpression(self.strct, inExecution: updated_execution)
     guard case (.Ok(let value), let updated_execution) = maybe_value else {
       return .Error(
         Error(withMessage: "\(self.strct) cannot be evaluated: \(maybe_value.0.error()!)"))
@@ -444,7 +452,8 @@ extension FieldAccessExpression: EvaluatableLValueExpression {
 
 extension KeysetExpression: EvaluatableExpression {
   public func evaluate(execution: ProgramExecution) -> (Result<P4Value>, ProgramExecution) {
-    return self.key.evaluate(execution: execution)
+    //return self.key.evaluate(execution: execution)
+    return EvaluateExpression(self.key, inExecution: execution)
   }
 
   public func type() -> P4Type {
diff --git a/Sources/P4Runtime/Parser.swift b/Sources/P4Runtime/Parser.swift
index 1fe6812..e2db657 100644
--- a/Sources/P4Runtime/Parser.swift
+++ b/Sources/P4Runtime/Parser.swift
@@ -21,7 +21,8 @@ import P4Lang
 extension ParserAssignmentStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
     let updated_execution = execution
-    let result = self.value.evaluate(execution: updated_execution)
+    //let result = self.value.evaluate(execution: updated_execution)
+    let result = EvaluateExpression(self.value, inExecution: updated_execution)
     guard case (.Ok(let value), let updated_execution) = result else {
       return (ControlFlow.Error, execution.setError(error: result.0.error()!))
     }
@@ -43,19 +44,23 @@ extension ParserStateDirectTransition: EvaluatableParserState {
   ) -> (any EvaluatableParserState, Common.ProgramExecution) {
     var program = program.enter_scope()
 
-    for statement in statements {
-      let (control_flow, next_program) = statement.evaluate(execution: program)
-      switch control_flow {
-      case .Next: program = next_program  // Ok!
-      case .Error: return (reject, next_program)
-      default:
-        return (
-          reject,
-          next_program.setError(
-            error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
-        )
-      }
+
+    let (control_flow, next_execution) = ExecuteStatement(statements, handleResult: { (control_flow, execution) in
+      return (control_flow, execution)
+      }, inExecution: program)
+
+
+    switch control_flow {
+    case .Next: program = next_execution
+    case .Error: return (reject, next_execution.exit_scope())
+    default:
+      return (
+        reject,
+        next_execution.exit_scope().setError(
+          error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
+      )
     }
+
     let res = program.scopes.lookup(identifier: get_next_state())
 
     if case .Ok(let value) = res {
@@ -79,7 +84,6 @@ extension ParserStateDirectTransition: EvaluatableParserState {
 }
 
 extension ParserStateNoTransition: EvaluatableParserState {
-
   public func execute(
     program: Common.ProgramExecution
   ) -> (any EvaluatableParserState, Common.ProgramExecution) {
@@ -96,28 +100,30 @@ extension ParserStateNoTransition: EvaluatableParserState {
 }
 
 extension ParserStateSelectTransition: EvaluatableParserState {
-
   public func execute(
     program: Common.ProgramExecution
   ) -> (any EvaluatableParserState, Common.ProgramExecution) {
     var program = program.enter_scope()
 
-    // First, evaluate the statements.
-    for statement in statements {
-      let (control_flow, next_program) = statement.evaluate(execution: program)
-      switch control_flow {
-      case .Next: program = next_program  // Ok!
-      case .Error: return (reject, next_program)
-      default:
-        return (
-          reject,
-          next_program.setError(
-            error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
-        )
-      }
+    let (control_flow, next_execution) = ExecuteStatement(statements, handleResult: { (control_flow, execution) in
+      return (control_flow, execution)
+      }, inExecution: program)
+
+
+    switch control_flow {
+    case .Next: program = next_execution
+    case .Error: return (reject, next_execution.exit_scope())
+    default:
+      return (
+        reject,
+        next_execution.exit_scope().setError(
+          error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
+      )
     }
 
-    switch self.selectExpression.evaluate(execution: program) {
+
+    //switch self.selectExpression.evaluate(execution: program) {
+    switch EvaluateExpression(self.selectExpression, inExecution: program) {
     case (.Ok(let value), let program):
       if value.type().dataType().eq(rhs: self) {
         return (value.dataValue() as! EvaluatableParserState, program.exit_scope())
@@ -156,10 +162,8 @@ extension Parser: LibraryCallable {
       withValue: P4Value(reject, P4Type.ReadOnly(reject.type())))
 
     // Add initial values to the global scope
-    if let initial = execution.initial_values() {
-      for (name, value) in initial {
-        execution = execution.declare(identifier: name, withValue: value)
-      }
+    for (name, value) in execution.getGlobalValues() {
+      execution = execution.declare(identifier: name, withValue: value)
     }
 
     // First, add every state to the scope!
diff --git a/Sources/P4Runtime/Runtime.swift b/Sources/P4Runtime/Runtime.swift
index e2f254e..0e2b45f 100644
--- a/Sources/P4Runtime/Runtime.swift
+++ b/Sources/P4Runtime/Runtime.swift
@@ -29,22 +29,22 @@ public struct ParserRuntime: CustomStringConvertible {
     self.initialValues = .none
   }
 
-  init(parser: Parser, withInitialValues initial: VarValueScopes?) {
+  init(parser: Parser, withGlobalValues initial: VarValueScopes?) {
     self.parser = parser
     self.initialValues = initial
   }
 
   /// Create a parser runtime from a P4 program
   public static func create(program: P4Lang.Program) -> Result<ParserRuntime> {
-    return ParserRuntime.create(program: program, withInitialValues: .none)
+    return ParserRuntime.create(program: program, withGlobalValues: .none)
   }
 
   public static func create(
-    program: P4Lang.Program, withInitialValues initial: VarValueScopes?
+    program: P4Lang.Program, withGlobalValues initial: VarValueScopes?
   ) -> Result<ParserRuntime> {
     return switch program.starting_parser() {
     case .Ok(let parser):
-      .Ok(P4Runtime.ParserRuntime(parser: parser, withInitialValues: initial))
+      .Ok(P4Runtime.ParserRuntime(parser: parser, withGlobalValues: initial))
     case .Error(let error): .Error(error)
     }
   }
@@ -52,12 +52,10 @@ public struct ParserRuntime: CustomStringConvertible {
   /// Run a P4 parser with no arguments
   public func run() -> Result<(ParserState, ProgramExecution)> {
     return self.run(withArguments: ArgumentList([]))
+
   }
 
-  /// Run the P4 parser on a given packet
-  public func run(withArguments arguments: ArgumentList) -> Result<(ParserState, ProgramExecution)>
-  {
-
+  public func run(withArguments arguments: ArgumentList) -> Result<(ParserState, ProgramExecution)> {
     let pe =
       if let initial = initialValues {
         ProgramExecution(withGlobalValues: initial)
@@ -65,6 +63,19 @@ public struct ParserRuntime: CustomStringConvertible {
         ProgramExecution()
       }
 
+    return self.run(withArguments: arguments, inExecution: pe)
+  }
+
+  /// Run the P4 parser on a given packet
+  public func run(withArguments arguments: ArgumentList, inExecution pe: ProgramExecution) -> Result<(ParserState, ProgramExecution)>
+  {
+
+    let pe = if let globals = initialValues {
+      pe.setGlobalValues(globals)
+    } else {
+      pe
+    }
+
     let (end_state, execution) = parser.call(execution: pe, arguments: arguments)
     if let error = execution.getError() {
       return .Error(error)
diff --git a/Sources/P4Runtime/Statements.swift b/Sources/P4Runtime/Statements.swift
index 16af979..4400b0f 100644
--- a/Sources/P4Runtime/Statements.swift
+++ b/Sources/P4Runtime/Statements.swift
@@ -20,29 +20,31 @@ import P4Lang
 
 extension BlockStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
-    var execution = execution
-    for s in self.statements {
-      let (control_flow, next_execution) = s.evaluate(execution: execution)
-      switch control_flow {
-      case ControlFlow.Return(let value): return (ControlFlow.Return(value), next_execution)
-      case ControlFlow.Next: execution = next_execution
-      case ControlFlow.Error: return (ControlFlow.Error, next_execution)
-      default:
-        return (
-          ControlFlow.Next,
-          next_execution.setError(
-            error: Error(withMessage: "Invalid control flow \(control_flow) in block statement"))
-        )
-      }
-    }
-    return (ControlFlow.Next, execution)
+    print("I am going to evaluate a block statement?")
+    return ExecuteStatement(
+      self.statements,
+      handleResult: { (cf, execution) in
+        switch cf {
+        case ControlFlow.Return(let value): return (ControlFlow.Return(value), execution)
+        case ControlFlow.Next: return (cf, execution)
+        case ControlFlow.Error: return (ControlFlow.Error, execution)
+        default:
+          return (
+            ControlFlow.Error,
+            execution.setError(
+              error: Error(withMessage: "Invalid control flow \(cf) in block statement"))
+          )
+        }
+      },
+      inExecution: execution)
   }
 }
 
 extension VariableDeclarationStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
     guard
-      case (.Ok(let initial_value), let execution) = self.initializer.evaluate(execution: execution)
+      //case (.Ok(let initial_value), let execution) = self.initializer.evaluate(execution: execution)
+      case (.Ok(let initial_value), let execution) = EvaluateExpression(self.initializer, inExecution: execution)
     else {
       return (
         ControlFlow.Error,
@@ -58,8 +60,8 @@ extension VariableDeclarationStatement: EvaluatableStatement {
 extension ConditionalStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
     guard
-      case (.Ok(let evaluated_condition), let execution) = self.condition.evaluate(
-        execution: execution)
+      //case (.Ok(let evaluated_condition), let execution) = self.condition.evaluate(execution: execution)
+      case (.Ok(let evaluated_condition), let execution) = EvaluateExpression(self.condition, inExecution: execution)
     else {
       return (
         ControlFlow.Error,
@@ -107,7 +109,8 @@ extension ExpressionStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
 
     // Evaluate, there might be side effects!
-    return switch self.expression.evaluate(execution: execution) {
+    //return switch self.expression.evaluate(execution: execution) {
+    return switch EvaluateExpression(self.expression, inExecution: execution) {
     case (.Ok(_), let updated_context): (ControlFlow.Next, updated_context)
     case (.Error(let e), let updated_context):
       (ControlFlow.Next, updated_context.setError(error: e))
@@ -117,7 +120,8 @@ extension ExpressionStatement: EvaluatableStatement {
 
 extension ReturnStatement: EvaluatableStatement {
   public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
-    return switch self.value.evaluate(execution: execution) {
+    //return switch self.value.evaluate(execution: execution) {
+    return switch EvaluateExpression(self.value, inExecution: execution) {
     case (.Ok(let v), let execution): (ControlFlow.Return(v), execution)
     case (.Error(let e), let execution): (ControlFlow.Error, execution.setError(error: e))
     }
diff --git a/Tests/p4rseTests/ArrayTests.swift b/Tests/p4rseTests/ArrayTests.swift
index 6fa800a..b71d537 100644
--- a/Tests/p4rseTests/ArrayTests.swift
+++ b/Tests/p4rseTests/ArrayTests.swift
@@ -49,7 +49,7 @@ import TreeSitterP4
     ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
@@ -101,7 +101,7 @@ import TreeSitterP4
     ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.reject)
@@ -128,7 +128,7 @@ import TreeSitterP4
     ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
@@ -155,7 +155,7 @@ import TreeSitterP4
     ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
@@ -187,7 +187,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
@@ -216,7 +216,7 @@ import TreeSitterP4
     ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
@@ -249,7 +249,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
 
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
diff --git a/Tests/p4rseTests/InterloperTests.swift b/Tests/p4rseTests/InterloperTests.swift
new file mode 100644
index 0000000..f6f3640
--- /dev/null
+++ b/Tests/p4rseTests/InterloperTests.swift
@@ -0,0 +1,114 @@
+// p4rse, Copyright 2026, Will Hawkins
+//
+// This file is part of p4rse.
+//
+// This file is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+import Common
+import Foundation
+import Macros
+import P4Runtime
+import P4Lang
+import SwiftTreeSitter
+import Testing
+import TreeSitter
+import TreeSitterP4
+
+@testable import P4Compiler
+
+@Test func test_statement_interloper() async throws {
+  let simple_parser_declaration = """
+      parser main_parser() {
+        state starts {
+          bool where_to = false;
+          int va = 5;
+          transition accept;
+        }
+        state start {
+          bool where_to = true;
+          where_to = true;
+          transition select (where_to) {
+            false: reject;
+            true: starts;
+          };
+        }
+      };
+    """
+  
+  let program = try #UseOkResult(Program.Compile(simple_parser_declaration))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program))
+
+  var statements_executed: [String] = Array()
+
+  let pe = ProgramExecution().setStatementInterloper({ (statement, cf, execution) in
+    statements_executed.append("\(statement)")
+  })
+
+  let (state_result, _) = try! #UseOkResult(runtime.run(withArguments: ArgumentList(), inExecution: pe))
+
+  #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
+
+  #expect(statements_executed[0].hasPrefix("VariableDeclarationStatement"))
+  #expect(statements_executed[1].hasPrefix("ParserAssignmentStatement"))
+  // Moved into starts
+  #expect(statements_executed[2].hasPrefix("VariableDeclarationStatement"))
+  #expect(statements_executed[3].hasPrefix("VariableDeclarationStatement"))
+}
+
+@Test func test_expression_interloper() async throws {
+  let simple_parser_declaration = """
+      parser main_parser() {
+        state starts {
+          bool where_to = false;
+          int va = 5;
+          transition accept;
+        }
+        state start {
+          bool where_to = true;
+          where_to = true;
+          transition select (where_to) {
+            false: reject;
+            true: starts;
+          };
+        }
+      };
+    """
+  
+  let program = try #UseOkResult(Program.Compile(simple_parser_declaration))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program))
+
+  var expressions_evaluated: [String] = Array()
+
+  let pe = ProgramExecution().setExpressionInterloper() { expression, result, execution in 
+    print("Expression: \(expression)")
+    expressions_evaluated.append("\(expression)")
+  }
+
+  let (state_result, _) = try! #UseOkResult(runtime.run(withArguments: ArgumentList(), inExecution: pe))
+
+  #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
+
+  #expect(expressions_evaluated[0].hasPrefix("Value: true of Boolean"))
+  #expect(expressions_evaluated[1].hasPrefix("Value: true of Boolean"))
+  #expect(expressions_evaluated[2].hasPrefix("where_to"))
+  #expect(expressions_evaluated[3].hasPrefix("Value: false of Boolean"))
+  #expect(expressions_evaluated[4].hasPrefix("KeysetExpression"))
+  #expect(expressions_evaluated[5].hasPrefix("Value: true of Boolean"))
+  #expect(expressions_evaluated[6].hasPrefix("KeysetExpression"))
+  #expect(expressions_evaluated[7].hasPrefix("SelectCaseExpression"))
+  #expect(expressions_evaluated[8].hasPrefix("SelectExpression"))
+  // Moved into starts
+  #expect(expressions_evaluated[9].hasPrefix("Value: false of Boolean"))
+  #expect(expressions_evaluated[10].hasPrefix("Value: 5 of Int"))
+}
diff --git a/Tests/p4rseTests/StructTests.swift b/Tests/p4rseTests/StructTests.swift
index 5da57be..d4a15a1 100644
--- a/Tests/p4rseTests/StructTests.swift
+++ b/Tests/p4rseTests/StructTests.swift
@@ -57,7 +57,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
@@ -151,7 +151,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.reject)
 }
@@ -186,7 +186,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
@@ -220,7 +220,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.reject)
 }
@@ -266,7 +266,7 @@ import TreeSitterP4
       ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
@@ -302,7 +302,7 @@ import TreeSitterP4
 
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
@@ -375,7 +375,7 @@ import TreeSitterP4
       ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
@@ -423,7 +423,7 @@ import TreeSitterP4
       ])))
   let program = try #UseOkResult(
     Program.Compile(simple_parser_declaration, withGlobalInstances: test_declarations))
-  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withInitialValues: test_values))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program, withGlobalValues: test_values))
   let (state_result, _) = try! #UseOkResult(runtime.run())
   #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
 }
diff --git a/Tests/p4rseTests/SupportTests.swift b/Tests/p4rseTests/SupportTests.swift
index 38b24d2..aad8ed8 100644
--- a/Tests/p4rseTests/SupportTests.swift
+++ b/Tests/p4rseTests/SupportTests.swift
@@ -35,10 +35,15 @@ struct StringConvertible: CustomStringConvertible {
 
 @Test func test_result_type_description_not_convertible() async throws {
     let result: Result<NotStringConvertible> = Result.Ok(NotStringConvertible());
-    #expect(result.description == "Ok")
+    #expect("\(result)" == "Ok(Tests.NotStringConvertible())")
 }
 
 @Test func test_result_type_description_convertible() async throws {
     let result: Result<StringConvertible> = Result.Ok(StringConvertible());
-    #expect(result.description == "CONVERTED")
+    #expect("\(result)" == "Ok: CONVERTED")
+}
+
+@Test func test_result_type_p4value_convertible() async throws {
+    let result = Result.Ok(P4Value(P4IntValue(withValue: 5)))
+    #expect("\(result)" == "Ok: Value: 5 of Int type of type Int")
 }
\ No newline at end of file
diff --git a/tree-sitter-p4/grammar.js b/tree-sitter-p4/grammar.js
index 5f33005..ba28e70 100644
--- a/tree-sitter-p4/grammar.js
+++ b/tree-sitter-p4/grammar.js
@@ -111,8 +111,7 @@ export default grammar({
 
         // Parser statements
         parserStatements: $ => repeat1($.parserStatement),
-        parserStatement: $ => choice($.conditionalStatement, $.parserBlockStatement, $.expressionStatement, $.assignmentStatement, $.variableDeclaration), // Limited, so far.
-        parserBlockStatement: $ => seq(optional($.annotations), '{', $.parserStatements, '}'),
+        parserStatement: $ => choice($.conditionalStatement, $.expressionStatement, $.assignmentStatement, $.variableDeclaration), // Limited, so far.
         parserTransitionStatement: $ => seq($.transition, $.transitionSelectionExpression, $._semicolon),
 
         // Expressions