diff --git a/Sources/Common/Scope.swift b/Sources/Common/Scope.swift
index 7a7d290..ac0e2df 100644
--- a/Sources/Common/Scope.swift
+++ b/Sources/Common/Scope.swift
@@ -15,7 +15,13 @@
 // 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 struct Scope<T>: CustomStringConvertible {
+public struct Scope<T>: CustomStringConvertible, Sequence {
+  public typealias Element = T
+  public typealias Iterator = Dictionary<Identifier, T>.Values.Iterator
+  public func makeIterator() -> Iterator {
+    self.symbols.values.makeIterator()
+  }
+
   var symbols: [Identifier: T] = Dictionary()
   public init() {}
 
@@ -45,7 +51,7 @@ public struct Scope<T>: CustomStringConvertible {
   }
 }
 
-public struct Scopes<T>: CustomStringConvertible {
+public struct Scopes<T>: CustomStringConvertible, Sequence {
   var scopes: [Scope<T>] = Array()
 
   public init() {}
@@ -117,6 +123,12 @@ public struct Scopes<T>: CustomStringConvertible {
     return .Error(Error(withMessage: "Cannot find \(identifier) in lexical scope."))
   }
 
+  public typealias Element = T
+  public typealias Iterator = Dictionary<Identifier, T>.Values.Iterator
+  public func makeIterator() -> Iterator {
+    scopes.last?.makeIterator() ?? Scope<T>().makeIterator()
+  }
+
   public var count: Int {
     scopes.count
   }
diff --git a/Sources/P4Compiler/Parser.swift b/Sources/P4Compiler/Parser.swift
index 2617ec8..9c55be7 100644
--- a/Sources/P4Compiler/Parser.swift
+++ b/Sources/P4Compiler/Parser.swift
@@ -144,8 +144,8 @@ public struct Parser {
 
   public struct TransitionStatement {
     static func Compile(
-      node: Node, inTree tree: MutableTree, withScope scopes: LexicalScopes
-    ) -> Result<(ParserTransitionStatement, LexicalScopes)> {
+      node: Node, inTree tree: MutableTree, forState state_identifier: Common.Identifier, withStatements stmts: [EvaluatableStatement], withScope scopes: LexicalScopes
+    ) -> Result<(ParserState, LexicalScopes)> {
 
       #RequireNodeType<Node, (EvaluatableStatement, LexicalScopes)>(
         node: node, type: "parserTransitionStatement", nice_type_name: "parser transition statement"
@@ -171,7 +171,7 @@ public struct Parser {
           node: next_node, inTree: tree, withScopes: scopes)
         if case .Ok(let next_state) = maybe_parsed_next_state {
           return .Ok(
-            (ParserTransitionStatement(withNextState: next_state), scopes))
+            (ParserStateDirectTransition(name: state_identifier, withStatements: stmts, withNextState: next_state), scopes))
         } else {
           return .Error(
             Error(
@@ -187,7 +187,7 @@ public struct Parser {
       {
       case .Ok(let tse):
         .Ok(
-          (ParserTransitionStatement(withTransitionExpression: tse! as! SelectExpression), scopes))
+          (ParserStateSelectTransition(name: state_identifier, withStatements: stmts, withTransitioniExpression: tse as! SelectExpression), scopes))
       case .Error(let e): .Error(e)
       }
     }
@@ -287,18 +287,8 @@ public struct Parser {
           ErrorOnNode(node: node, withError: "Missing transition statement of state declaration"))
       }
       currentChild = node.child(at: currentChildIdx)
-      switch TransitionStatement.Compile(
-        node: currentChild!, inTree: tree, withScope: current_scopes)
-      {
-      case .Ok(let (transition_statement, new_scopes)):
-        return Result.Ok(
-          (
-            ParserState(
-              name: state_identifier, withStatements: parsed_s,
-              withTransition: transition_statement), new_scopes
-          ))
-      case .Error(let e): return .Error(e)
-      }
+      return TransitionStatement.Compile(
+        node: currentChild!, inTree: tree, forState: state_identifier, withStatements: parsed_s, withScope: current_scopes)
     }
   }
 
@@ -326,14 +316,13 @@ public struct Parser {
 
     var error: Error? = .none
 
-    var parser_scopes = scopes
-
     // TODO: Assert that there is only one.
     captures[0].node.enumerateChildren { parser_state in
-      switch Parser.State.Compile(node: parser_state, inTree: tree, withLexicalScopes: scopes) {
-      case Result.Ok(let (state, new_parser_scopes)):
+      switch Parser.State.Compile(
+        node: parser_state, inTree: tree, withLexicalScopes: scopes.enter())
+      {
+      case Result.Ok(let (state, _)):
         parser.states = parser.states.append(state: state)
-        parser_scopes = new_parser_scopes
       case Result.Error(let e): error = e
       }
     }
@@ -342,6 +331,6 @@ public struct Parser {
       return .Error(error)
     }
 
-    return Result.Ok((parser, parser_scopes))
+    return Result.Ok((parser, scopes))
   }
-}
+}
\ No newline at end of file
diff --git a/Sources/P4Compiler/Program.swift b/Sources/P4Compiler/Program.swift
index daee625..df21b7a 100644
--- a/Sources/P4Compiler/Program.swift
+++ b/Sources/P4Compiler/Program.swift
@@ -62,12 +62,13 @@ public struct Program {
         node: parser_declaration.nodes[1], inTree: tree, withLexicalScopes: program_scope)
       {
       case Result.Ok((let parser, let new_program_scope)):
-        program.types.append(parser)
-        program_scope = new_program_scope
+        program_scope = new_program_scope.declare(identifier: parser.name, withValue: parser)
       case Result.Error(let error): return Result.Error(error)
       }
     }
 
+    // Any of the types that are in the top-level scope should go into the program!
+    program.types = Array(program_scope)
     return Result.Ok(program)
   }
 }
diff --git a/Sources/P4Lang/Expressions.swift b/Sources/P4Lang/Expressions.swift
index e69de29..c6b82ab 100644
--- a/Sources/P4Lang/Expressions.swift
+++ b/Sources/P4Lang/Expressions.swift
@@ -0,0 +1,59 @@
+// 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
+
+public struct KeysetExpression {
+  public let key: EvaluatableExpression
+  public let next_state_identifier: Identifier
+  public let next_state: ParserState?
+
+  public init(withKey key: EvaluatableExpression, withNextState next_state_id: Identifier) {
+    self.key = key
+    self.next_state_identifier = next_state_id
+    self.next_state = .none
+  }
+  public init(
+    withKey key: EvaluatableExpression, withNextState next_state_id: Identifier,
+    withNextState next_state: ParserState
+  ) {
+    self.key = key
+    self.next_state_identifier = next_state_id
+    self.next_state = next_state
+  }
+
+}
+
+public struct SelectExpression {
+  public let selector: EvaluatableExpression
+  public let keyset_expressions: [KeysetExpression]
+
+  public init(
+    withSelector selector: EvaluatableExpression, withKeysetExpressions kses: [KeysetExpression]
+  ) {
+    self.selector = selector
+    self.keyset_expressions = kses
+  }
+
+  public func append_checked_kse(kse: KeysetExpression) -> SelectExpression {
+    var new_kse = self.keyset_expressions
+    new_kse.append(kse)
+    return SelectExpression(
+      withSelector: self.selector, withKeysetExpressions: new_kse)
+  }
+}
+
diff --git a/Sources/P4Lang/Instantiation.swift b/Sources/P4Lang/Instantiation.swift
deleted file mode 100644
index 7a0899d..0000000
--- a/Sources/P4Lang/Instantiation.swift
+++ /dev/null
@@ -1,22 +0,0 @@
-// 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
-
-public struct Instantiation {
-
-}
diff --git a/Sources/P4Lang/Parser.swift b/Sources/P4Lang/Parser.swift
index f1f0b3d..ebb664c 100644
--- a/Sources/P4Lang/Parser.swift
+++ b/Sources/P4Lang/Parser.swift
@@ -35,152 +35,100 @@ public struct ParserAssignmentStatement {
   }
 }
 
-public struct KeysetExpression {
-  public let key: EvaluatableExpression
-  public let next_state_identifier: Identifier
-  public let next_state: ParserState?
+/// A P4 Parser State
+/// 
+/// Note: A P4 Parser State is both a type and a value.
+public class ParserState: P4Type, P4Value, Equatable, CustomStringConvertible{
+    public static func == (lhs: ParserState, rhs: ParserState) -> Bool {
+        return lhs.state == rhs.state 
+    }
 
-  public init(withKey key: EvaluatableExpression, withNextState next_state_id: Identifier) {
-    self.key = key
-    self.next_state_identifier = next_state_id
-    self.next_state = .none
-  }
-  public init(
-    withKey key: EvaluatableExpression, withNextState next_state_id: Identifier,
-    withNextState next_state: ParserState
-  ) {
-    self.key = key
-    self.next_state_identifier = next_state_id
-    self.next_state = next_state
-  }
+    public func eq(rhs: any Common.P4Type) -> Bool {
+      return switch rhs  {
+        case is ParserState: true
+        default: false
+      }
+    }
 
-}
+    public func type() -> any Common.P4Type {
+        return self
+    }
 
-public struct SelectExpression {
-  public let selector: EvaluatableExpression
-  public let keyset_expressions: [KeysetExpression]
-
-  public init(
-    withSelector selector: EvaluatableExpression, withKeysetExpressions kses: [KeysetExpression]
-  ) {
-    self.selector = selector
-    self.keyset_expressions = kses
-  }
-
-  public func append_checked_kse(kse: KeysetExpression) -> SelectExpression {
-    var new_kse = self.keyset_expressions
-    new_kse.append(kse)
-    return SelectExpression(
-      withSelector: self.selector, withKeysetExpressions: new_kse)
-  }
-}
-
-public struct ParserTransitionStatement {
-  public let next_state: Identifier?
-  public let transition_expression: SelectExpression?
-
-  public init() {
-    self.next_state = .none
-    self.transition_expression = .none
-  }
-
-  public init(withTransitionExpression transition_expression: SelectExpression) {
-    self.next_state = .none
-    self.transition_expression = transition_expression
-  }
-
-  public init(withNextState next_state: Identifier) {
-    self.next_state = next_state
-    self.transition_expression = .none
-  }
-}
-
-public class ParserState: Equatable, CustomStringConvertible, Comparable {
+    public func eq(rhs: any Common.P4Value) -> Bool {
+      return switch rhs  {
+        case let other as ParserState: self.state == other.state
+        default: false
+      }
+    }
 
   public private(set) var state: Identifier
   public private(set) var statements: [EvaluatableStatement]
-  public private(set) var transition: ParserTransitionStatement?
-  public private(set) var next_state: ParserState?
-
-  public static func < (lhs: ParserState, rhs: ParserState) -> Bool {
-    // If lhs transitions to rhs, then return true. Otherwise, return false.
-
-    // TODO!!
-    return false
-  }
 
   public var description: String {
     return "Name: \(state)"
   }
 
-  public static func == (lhs: ParserState, rhs: ParserState) -> Bool {
-    return lhs.state == rhs.state
-  }
-
   /// Construct a ParserState
   public init(
-    name: Identifier, withStatements stmts: [EvaluatableStatement]?,
-    withTransition transitionStatement: ParserTransitionStatement
+    name: Identifier, withStatements stmts: [EvaluatableStatement],
   ) {
     state = name
-    transition = transitionStatement
-    statements = stmts ?? Array()
-  }
-
-  public func semantic_check(states: ParserStates) -> Bool {
-    guard let transition = transition else {
-      return self == accept || self == reject
-    }
-
-    if let next_state = transition.next_state,
-      let next_state = states.find(withIdentifier: next_state)
-    {
-      self.next_state = next_state
-      return true
-    }
-
-    return false
+    statements = stmts
   }
 
   /// (private) constructor (no transition)
   ///
   /// accept and reject are the only final states and they are constructed internally.
-  init(name: Identifier) {
+  private init(name: Identifier) {
     state = name
-    transition = .none
     statements = Array()
   }
+}
 
-  public func direct_transition() -> Bool {
-    return
-      if let transition = self.transition,
-      transition.next_state != nil
-    {
-      true
-    } else {
-      false
-    }
+
+public class ParserStateDirectTransition: ParserState {
+
+  private let next_state: Identifier
+
+  public init(name: Identifier, withStatements stmts: [EvaluatableStatement], withNextState next_state: Identifier) {
+    self.next_state = next_state
+    super.init(name: name, withStatements: stmts)
+  }
+
+  public override var description: String {
+    return "State (Name: \(super.state) (direct transition))"
+  }
+
+  public func get_next_state() -> Identifier {
+    return self.next_state
   }
 }
 
-/// A P4 parser state type
-public struct P4ParserState: P4Type {
-  public static func create() -> any P4Type {
-    return P4ParserState()
+public class ParserStateNoTransition: ParserState {
+  public override init(name: Identifier, withStatements stmts: [any EvaluatableStatement]) {
+    super.init(name: name, withStatements: stmts)
   }
-  public var description: String {
-    return "Parser State"
-  }
-  public func eq(rhs: any P4Type) -> Bool {
-    return switch rhs {
-    case is P4ParserState: true
-    default: false
-    }
+  public override var description: String {
+    return "State (Name: \(super.state) (no transition))"
   }
 }
 
-nonisolated(unsafe) public let accept: ParserState = ParserState(name: Identifier(name: "accept"))
-nonisolated(unsafe) public let reject: ParserState = ParserState(name: Identifier(name: "reject"))
+public class ParserStateSelectTransition: ParserState {
+
+  public let selectExpression: SelectExpression
+
+  public override var description: String {
+    return "State (Name: \(super.state) (select transition))"
+  }
+
+  public init(name: Identifier, withStatements stmts: [any EvaluatableStatement], withTransitioniExpression te: SelectExpression) {
+    self.selectExpression = te
+    super.init(name: name, withStatements: stmts)
+  }
+}
+
+nonisolated(unsafe) public let accept = ParserStateNoTransition(name: Identifier(name: "accept"), withStatements: [])
+nonisolated(unsafe) public let reject = ParserStateNoTransition(name: Identifier(name: "reject"), withStatements: [])
 
 public struct ParserStates {
   public var states: [ParserState] = Array()
@@ -198,22 +146,6 @@ public struct ParserStates {
     return .none
   }
 
-  public func semantic_check() -> Result<()> {
-    // Check whether all the states referred to in the transition statements are
-    // valid.
-    let errors = states.filter { state in
-      return !state.semantic_check(states: self)
-    }.map { state in
-      return Result<()>.Error(Error(withMessage: "State \(state) has invalid transition"))
-    }
-
-    if !errors.isEmpty {
-      return errors[0]
-    }
-
-    return .Ok(())
-  }
-
   public init() {
     self.states = Array()
   }
@@ -229,7 +161,21 @@ public struct ParserStates {
   }
 }
 
-public struct Parser: P4Type {
+/// A P4 Parser
+/// 
+/// Note: A Parser is both a type _and_ a value.
+public struct Parser: P4Type, P4Value {
+    public func type() -> any Common.P4Type {
+        return self 
+    }
+
+  public func eq(rhs: any Common.P4Type) -> Bool {
+    return switch rhs {
+    case is Parser: true
+    default: false
+    }
+  }
+
   public var states: ParserStates
 
   public var name: Identifier
@@ -239,10 +185,6 @@ public struct Parser: P4Type {
     self.name = name
   }
 
-  public static func create() -> any P4Type {
-    return Parser(withName: Identifier(name: ""))
-  }
-
   public func findStartState() -> ParserState? {
     for state in states.states {
       if state.state == Identifier(name: "start") {
@@ -252,19 +194,14 @@ public struct Parser: P4Type {
     return .none
   }
 
-  public func semantic_check() -> Result<()> {
-    return self.states.semantic_check()
+  public func eq(rhs: any P4Value) -> Bool {
+    return switch rhs {
+    case let other as Parser: self.name == other.name
+    default: false
+    }
   }
 
   public var description: String {
     return "Parser"
   }
-
-  public func eq(rhs: P4Type) -> Bool {
-    return if let parser_rhs = rhs as? Parser {
-      self.name == parser_rhs.name
-    } else {
-      false
-    }
-  }
 }
diff --git a/Sources/P4Runtime/Expressions.swift b/Sources/P4Runtime/Expressions.swift
index d2835ad..06afca1 100644
--- a/Sources/P4Runtime/Expressions.swift
+++ b/Sources/P4Runtime/Expressions.swift
@@ -24,7 +24,8 @@ extension KeysetExpression: EvaluatableExpression {
   }
 
   public func type() -> any Common.P4Type {
-    return P4ParserState.create()
+    // TODO
+    return reject
   }
 }
 
@@ -45,8 +46,9 @@ extension SelectExpression: EvaluatableExpression {
     }
   }
 
+  // TODO
   public func type() -> any Common.P4Type {
-    return P4ParserState.create()
+    return reject
   }
 }
 
diff --git a/Sources/P4Runtime/Parser.swift b/Sources/P4Runtime/Parser.swift
index 56a6523..39ddadd 100644
--- a/Sources/P4Runtime/Parser.swift
+++ b/Sources/P4Runtime/Parser.swift
@@ -32,39 +32,20 @@ extension ParserAssignmentStatement: EvaluatableStatement {
   }
 }
 
-public struct ParserStateDirectTransition: ParserStateInstance {
-
-  public func type() -> any Common.P4Type {
-    return P4ParserState.create()
-  }
-
-  public func eq(rhs: any Common.P4Value) -> Bool {
-    switch rhs {
-    case let state as ParserStateInstance: return currrent_state == state.state()
-    default: return false
-    }
-  }
-
-  public var description: String {
-    return "Instance of \(currrent_state)"
-  }
-
-  public let currrent_state: ParserState
-  public let next_state_identifier: Identifier
-
+extension ParserStateDirectTransition: EvaluatableParserState {
   public func execute(
     program: Common.ProgramExecution
-  ) -> (any ParserStateInstance, Common.ProgramExecution) {
+  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
     var program = program.enter_scope()
 
-    for statement in currrent_state.statements {
+    for statement in statements {
       program = statement.evaluate(execution: program)
     }
-    let res = program.scopes.lookup(identifier: next_state_identifier)
+    let res = program.scopes.lookup(identifier: get_next_state())
 
     if case .Ok(let value) = res {
-      if value.type().eq(rhs: P4ParserState.create()) {
-        return (value as! ParserStateInstance, program.exit_scope())
+      if value.type().eq(rhs: self) {
+        return (value as! EvaluatableParserState, program.exit_scope())
       }
     }
 
@@ -78,33 +59,15 @@ public struct ParserStateDirectTransition: ParserStateInstance {
   }
 
   public func state() -> P4Lang.ParserState {
-    return currrent_state
+    return self
   }
-
 }
 
-public struct ParserStateNoTransition: ParserStateInstance {
-
-  public func type() -> any Common.P4Type {
-    return P4ParserState.create()
-  }
-
-  public func eq(rhs: any Common.P4Value) -> Bool {
-    switch rhs {
-    case let state as ParserStateInstance: return currrent_state == state.state()
-    default: return false
-    }
-  }
-
-  public var description: String {
-    return "Instance of \(currrent_state)"
-  }
-
-  public let currrent_state: ParserState
+extension ParserStateNoTransition: EvaluatableParserState {
 
   public func execute(
     program: Common.ProgramExecution
-  ) -> (any ParserStateInstance, Common.ProgramExecution) {
+  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
     return (self, program)
   }
 
@@ -113,41 +76,27 @@ public struct ParserStateNoTransition: ParserStateInstance {
   }
 
   public func state() -> P4Lang.ParserState {
-    return currrent_state
+    return self
   }
 }
 
-public struct ParserStateSelectTransition: ParserStateInstance {
-  public func type() -> any Common.P4Type {
-    return P4ParserState.create()
-  }
-
-  public func eq(rhs: any Common.P4Value) -> Bool {
-    switch rhs {
-    case let state as ParserStateInstance: return currrent_state == state.state()
-    default: return false
-    }
-  }
-
-  public var description: String {
-    return "Instance of \(currrent_state)"
-  }
+extension ParserStateSelectTransition: EvaluatableParserState {
 
   public func execute(
     program: Common.ProgramExecution
-  ) -> (any ParserStateInstance, Common.ProgramExecution) {
+  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
     var program = program.enter_scope()
 
     // First, evaluate the statements.
-    for statement in currrent_state.statements {
+    for statement in statements {
       program = statement.evaluate(execution: program)
     }
 
     let res = self.selectExpression.evaluate(execution: program)
 
     if case .Ok(let value) = res {
-      if value.type().eq(rhs: P4ParserState.create()) {
-        return (value as! ParserStateInstance, program.exit_scope())
+      if value.type().eq(rhs: self) {
+        return (value as! EvaluatableParserState, program.exit_scope())
       }
     }
 
@@ -160,95 +109,32 @@ public struct ParserStateSelectTransition: ParserStateInstance {
   }
 
   public func state() -> P4Lang.ParserState {
-    return currrent_state
-  }
-
-  public let selectExpression: SelectExpression
-  public let currrent_state: ParserState
-}
-
-extension ParserState: Compilable {
-  public typealias ToCompile = ParserState
-  public typealias Compiled = ParserStateInstance
-  public static func compile(_ state: ToCompile) -> Result<Compiled> {
-
-    if state.direct_transition(),
-      let transition_statement = state.transition
-    {
-      return .Ok(
-        ParserStateDirectTransition(
-          currrent_state: state, next_state_identifier: transition_statement.next_state!))
-    }
-
-    if let transition_select_statement = state.transition,
-      let transition_select_expression = transition_select_statement.transition_expression
-    {
-
-      return .Ok(
-        ParserStateSelectTransition(
-          selectExpression: transition_select_expression, currrent_state: state))
-    }
-
-    return .Error(Error(withMessage: "Invalid parser state: No meaningful transition"))
+    return self
   }
 }
 
-extension ParserStates: Compilable {
-  public typealias ToCompile = ParserStates
-  public typealias Compiled = (ParserStateInstance, [ParserStateInstance])
-  public static func compile(_ parser: ToCompile) -> Result<Compiled> {
-    var compiled_states: [ParserStateInstance] = Array()
+extension Parser: ParserExecution {
+  public func execute(execution: ProgramExecution) -> (ParserState, ProgramExecution) {
+    var execution = execution.enter_scope()
 
-    compiled_states.append(ParserStateNoTransition(currrent_state: accept))
-    compiled_states.append(ParserStateNoTransition(currrent_state: reject))
+    execution = execution.declare(identifier: accept.state().state, withValue: accept)
+    execution = execution.declare(identifier: reject.state().state, withValue: reject)
 
-    var start_state: ParserStateInstance? = .none
-
-    // TODO: We assume that states are in transition-order!
-    for state in parser.states {
-      switch ParserState.compile(state) {
-      case .Ok(let compiled):
-        if compiled.state().state == Identifier(name: "start") {
-          start_state = compiled
-        }
-        compiled_states.append(compiled)
-      case .Error(let e): return .Error(e)
-      }
+    // First, add every state to the scope!
+    for state in self.states.states {
+      execution = execution.declare(identifier: state.state, withValue: state)
     }
 
-    // Now, find the start state:
-    if let start_state = start_state {
-      return .Ok((start_state, compiled_states))
-    } else {
-      return .Error(Error(withMessage: "No start state defined"))
+    guard let _current_state = self.findStartState(),
+    var current_state = _current_state as? EvaluatableParserState else {
+      return (reject, execution.setError(error: Error(withMessage: "Could not find the start state")))
     }
-  }
-}
 
-public class ParserInstance: ProgramExecution {
 
-  let states: [ParserStateInstance]
-  let start_state: ParserStateInstance
-
-  public init(start: ParserStateInstance, states: [ParserStateInstance]) {
-    start_state = start
-    self.states = states
-  }
-
-  public override var description: String {
-    return "Execution: \(super.description)\nStates: \(states)"
-  }
-}
-
-extension ParserInstance: Compilable {
-  public typealias ToCompile = Parser
-  public typealias Compiled = ParserInstance
-
-  public static func compile(_ parser: ToCompile) -> Result<Compiled> {
-    return switch ParserStates.compile(parser.states) {
-    case .Ok(let (start_state, states)):
-      Result.Ok(ParserInstance(start: start_state, states: states))
-    case .Error(let e): Result.Error(e)
+    // Evaluate until the state is either accept or reject.
+    while !current_state.done() && !execution.hasError() {
+      (current_state, execution) = current_state.execute(program: execution)
     }
+    return (current_state.state(), execution)
   }
-}
+}
\ No newline at end of file
diff --git a/Sources/P4Runtime/Protocols.swift b/Sources/P4Runtime/Protocols.swift
index 5a0866d..dae3e98 100644
--- a/Sources/P4Runtime/Protocols.swift
+++ b/Sources/P4Runtime/Protocols.swift
@@ -19,7 +19,7 @@ import Common
 import P4Lang
 
 public protocol Execution {
-  func execute() -> (ParserState, ProgramExecution)
+  func execute(execution: ProgramExecution) -> ProgramExecution
 }
 
 public protocol Compilable {
@@ -28,12 +28,12 @@ public protocol Compilable {
   static func compile(_: ToCompile) -> Result<Compiled>
 }
 
-public protocol ParserStateInstance: P4Value {
-  func execute(program: ProgramExecution) -> (ParserStateInstance, ProgramExecution)
+public protocol EvaluatableParserState: P4Value {
+  func execute(program: ProgramExecution) -> (EvaluatableParserState, ProgramExecution)
   func done() -> Bool
   func state() -> ParserState
 }
 
 public protocol ParserExecution {
-  func execute() -> (ParserState, ProgramExecution)
+  func execute(execution: ProgramExecution) -> (ParserState, ProgramExecution)
 }
diff --git a/Sources/P4Runtime/Runtime.swift b/Sources/P4Runtime/Runtime.swift
index 0429507..5f25a42 100644
--- a/Sources/P4Runtime/Runtime.swift
+++ b/Sources/P4Runtime/Runtime.swift
@@ -19,11 +19,11 @@ import Common
 import P4Lang
 
 /// The runtime for a parser
-public class ParserRuntime: CustomStringConvertible {
-  public var parser: ParserInstance
+public struct ParserRuntime: CustomStringConvertible {
+  public var parser: Parser
 
-  init(execution: ParserInstance) {
-    self.parser = execution
+  init(parser: Parser) {
+    self.parser = parser
   }
 
   /// Create a parser runtime from a P4 program
@@ -31,17 +31,15 @@ public class ParserRuntime: CustomStringConvertible {
 
     return switch program.starting_parser() {
     case .Ok(let parser):
-      switch ParserInstance.compile(parser) {
-      case .Ok(let execution): .Ok(P4Runtime.ParserRuntime(execution: execution))
-      case .Error(let error): .Error(error)
-      }
+      .Ok(P4Runtime.ParserRuntime(parser: parser))
     case .Error(let error): .Error(error)
     }
   }
 
   /// Run the P4 parser on a given packet
   public func run() -> Result<(ParserState, ProgramExecution)> {
-    let (end_state, execution) = parser.execute()
+
+    let (end_state, execution) = parser.execute(execution: ProgramExecution())
     if let error = execution.getError() {
       return .Error(error)
     }
@@ -51,25 +49,4 @@ public class ParserRuntime: CustomStringConvertible {
   public var description: String {
     return "Runtime:\nExecution: \(parser)"
   }
-}
-
-/// Instances of parsers are executable
-extension ParserInstance: ParserExecution {
-  public func execute() -> (ParserState, ProgramExecution) {
-    var execution = self as ProgramExecution
-
-    execution = execution.enter_scope()
-    // First, add every state to the scope!
-    for state in self.states {
-      execution = execution.declare(identifier: state.state().state, withValue: state)
-    }
-
-    var c = self.start_state
-
-    // Evaluate until the state is either accept or reject.
-    while !c.done() && !execution.hasError() {
-      (c, execution) = c.execute(program: execution)
-    }
-    return (c.state(), execution)
-  }
-}
+}
\ No newline at end of file
diff --git a/Sources/P4Runtime/Program.swift b/Sources/P4Runtime/Statements.swift
similarity index 100%
rename from Sources/P4Runtime/Program.swift
rename to Sources/P4Runtime/Statements.swift
diff --git a/Tests/p4rseTests/RuntimeTests.swift b/Tests/p4rseTests/RuntimeTests.swift
index 3c5ff68..2d33533 100644
--- a/Tests/p4rseTests/RuntimeTests.swift
+++ b/Tests/p4rseTests/RuntimeTests.swift
@@ -73,11 +73,12 @@ import TreeSitterP4
     """
 
   let program = try #UseOkResult(Program.Compile(simple_parser_declaration))
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program))
 
   #expect(
-    #RequireErrorResult<ParserRuntime>(
-      Error(withMessage: "No start state defined"),
-      P4Runtime.ParserRuntime.create(program: program)))
+    #RequireErrorResult<(ParserState, ProgramExecution)>(
+      Error(withMessage: "Could not find the start state"),
+      runtime.run()))
 }
 
 @Test func test_simple_parser_with_transition_select_expression() async throws {