Start Evaluation

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/Common/Execution.swift

@@ -17,12 +17,27 @@
 
 open class ProgramExecution: CustomStringConvertible {
     public var scopes: Scopes = Scopes()
+    var error: Error? 
 
     public init() {}
 
     open var description: String {
         return "Runtime:\nScopes: \(scopes)"
     }
+
+    public func hasError() -> Bool {
+        return self.error != nil
+    }
+
+    public func getError() -> Error? {
+        return self.error
+    }
+
+    public func setError(error: Error) -> ProgramExecution {
+        let npe = self
+        npe.error = error
+        return npe
+    }
 }
 
 
@@ -96,6 +111,15 @@ public struct Scopes: CustomStringConvertible {
         return s
     }
 
+    public func evaluate(identifier: Identifier) -> Result<P4Value> {
+        for scope in scopes {
+            if let vari = scope.lookup(identifier: identifier) {
+                return .Ok(vari.value)
+            }
+        }
+        return .Error(Error(withMessage: "Cannot find \(identifier) in scope."))
+    }
+
     public var count: Int {
         get {
             scopes.count

Sources/Common/ProgramTypes.swift

@@ -65,6 +65,12 @@ open class P4ValueBase<T: P4Type>: P4Value {
   }
 }
 
+extension P4ValueBase: EvaluatableExpression {
+  public func evaluate(execution: ProgramExecution) -> Result<P4Value> {
+    return .Ok(self)
+  }
+}
+
 /// The type for a P4 struct
 public struct P4Struct: P4Type {
   public let name: String
@@ -122,6 +128,7 @@ public class P4BooleanValue: P4ValueBase<P4Boolean> {
   }
 }
 
+
 /// A P4 int type
 public struct P4Int: P4Type {
   public static func create() -> any P4Type {

Sources/Common/Protocols.swift

@@ -20,7 +20,7 @@ public protocol EvaluatableExpression {
     /// - Parameters
     ///  - execution: The execution context in which to evaluate the expression
     /// - Returns: The value of expression
-    func evaluate(execution: ProgramExecution) -> P4Value
+    func evaluate(execution: ProgramExecution) -> Result<P4Value>
 }
 
 public protocol EvaluatableParserStatement {

Sources/Common/Support.swift

@@ -53,6 +53,13 @@ public enum Result<OKT>: Equatable {
         }
         return nil
     }
+
+    public func map<T>(block: (OKT) -> Result<T>) -> Result<T> {
+        switch self {
+            case .Ok(let ok): return block(ok)
+            case .Error(let e): return .Error(e)
+        } 
+    }
 }
 
 extension Result where OKT: CustomStringConvertible {

Sources/Lang/Parser.swift

@@ -25,8 +25,65 @@ public struct LocalElement {
 
 }
 
+public struct KeysetExpression {
+  public let key: EvaluatableExpression
+  public let next_state_name: String
+  public let next_state: ParserState?
+
+  public init(withKey key: EvaluatableExpression, withNextStateName next_state_name: String) {
+    self.key = key
+    self.next_state_name = next_state_name
+    self.next_state = .none
+  }
+  public init(
+    withKey key: EvaluatableExpression, withNextStateName next_state_name: String,
+    withNextState next_state: ParserState
+  ) {
+    self.key = key
+    self.next_state_name = next_state_name
+    self.next_state = next_state
+  }
+
+}
+
+public struct ParserTransitionSelectExpression {
+  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) -> ParserTransitionSelectExpression {
+    var new_kse = self.keyset_expressions
+    new_kse.append(kse)
+    return ParserTransitionSelectExpression(
+      withSelector: self.selector, withKeysetExpressions: new_kse)
+  }
+
+}
+
 public struct ParserTransitionStatement {
-  public init() {}
+  public let next_state_name: String?
+  public let transition_expression: ParserTransitionSelectExpression?
+
+  public init() {
+    self.next_state_name = .none
+    self.transition_expression = .none
+  }
+
+  public init(withTransitionExpression transition_expression: ParserTransitionSelectExpression) {
+    self.next_state_name = .none
+    self.transition_expression = transition_expression
+  }
+
+  public init(withNextState next_state_name: String) {
+    self.next_state_name = next_state_name
+    self.transition_expression = .none
+  }
 }
 
 public struct VariableDeclarationStatement {
@@ -36,16 +93,13 @@ public struct VariableDeclarationStatement {
   }
 }
 
-public struct ExpressionStatement {
+public class ParserState: Equatable, CustomStringConvertible {
-  public init() {}
-}
-
-public struct ParserState: Equatable, CustomStringConvertible {
 
   public private(set) var state_name: String
   public private(set) var local_elements: [EvaluatableParserStatement]
   public private(set) var statements: [EvaluatableParserStatement]
   public private(set) var transition: ParserTransitionStatement?
+  public private(set) var next_state: ParserState?
 
   public var description: String {
     return "Name: \(state_name)"
@@ -67,6 +121,37 @@ public struct ParserState: Equatable, CustomStringConvertible {
     self.statements = statements ?? Array()
   }
 
+  public func semantic_check(states: ParserStates) -> Bool {
+    guard let transition = transition else {
+      return self == accept || self == reject 
+    }
+
+    if let transition_select_expression = transition.transition_expression {
+      var updated_tse = ParserTransitionSelectExpression(
+        withSelector: transition_select_expression.selector, withKeysetExpressions: [])
+
+      for kse in transition_select_expression.keyset_expressions {
+        guard let next_state = states.find(withName: kse.next_state_name) else {
+          return false
+        }
+        let new_kse = KeysetExpression(
+          withKey: kse.key, withNextStateName: kse.next_state_name, withNextState: next_state)
+        updated_tse = updated_tse.append_checked_kse(kse: new_kse)
+      }
+      self.transition = ParserTransitionStatement(withTransitionExpression: updated_tse)
+      return true
+    }
+
+    if let next_state_name = transition.next_state_name,
+      let next_state = states.find(withName: next_state_name)
+    {
+      self.next_state = next_state
+      return true
+    }
+
+    return false
+  }
+
   /// (private) constructor (no transition)
   ///
   /// accept and reject are the only final states and they are constructed internally.
@@ -76,24 +161,76 @@ public struct ParserState: Equatable, CustomStringConvertible {
     local_elements = Array()
     statements = Array()
   }
+
+  public func direct_transition() -> Bool {
+    return
+      if let transition = self.transition,
+      transition.next_state_name != nil
+    {
+      true
+    } else {
+      false
+    }
+  }
 }
 
 public struct ParserStates {
   public var states: [ParserState] = Array()
+
+  public func count() -> Int {
+    return states.count
+  }
+
+  public func find(withName name: String) -> ParserState? {
+    for state in states {
+      if state.state_name == name {
+        return .some(state)
+      }
+    }
+    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()
+  }
+
+  private init(withStates states: [ParserState]) {
+    self.states = states
+  }
+
+  public func append(state: ParserState) -> ParserStates {
+    var new_states = self.states
+    new_states.append(state)
+    return ParserStates(withStates: new_states)
+  }
 }
 
 nonisolated(unsafe) public let accept: ParserState = ParserState(name: "accept")
 nonisolated(unsafe) public let reject: ParserState = ParserState(name: "reject")
 
 public struct Parser: P4Type {
-  public var states: [ParserState] = Array()
+  public var states: ParserStates
-  public var count: Int {
-    states.count
-  }
 
   public var name: Identifier
 
   public init(withName name: Identifier) {
+    self.states = ParserStates()
     self.name = name
   }
 
@@ -102,24 +239,38 @@ public struct Parser: P4Type {
   }
 
   public func findStartState() -> ParserState? {
-    for state in states {
+    for state in states.states {
       if state.state_name == "start" {
         return state
       }
     }
     return .none
   }
+
+  public func semantic_check() -> Result<()> {
+    return self.states.semantic_check()
+  }
 }
 
 public class ParserInstance: ProgramExecution {
 
+  public var state: ParserState
+
   private init(state: ParserState) {
     self.state = state
     super.init()
   }
 
   public static func create(_ parser: Parser) -> Result<ParserInstance> {
-        guard let start_state = parser.findStartState() else {
+
+    var augmented_parser = Parser(withName: parser.name)
+    augmented_parser.states = parser.states.append(state: accept).append(state: reject)
+
+    if case .Error(let e) = augmented_parser.semantic_check() {
+      return .Error(e)
+    }
+
+    guard let start_state = augmented_parser.findStartState() else {
       return Result.Error(Error(withMessage: "Could not find the start state"))
     }
     let new = ParserInstance(state: start_state)
@@ -127,8 +278,6 @@ public class ParserInstance: ProgramExecution {
     return Result.Ok(new)
   }
 
-    public var state: ParserState
-
   public func transition(toNextState state: ParserState) -> ParserInstance {
     let next = self
     next.state = state

Sources/Lang/Program.swift

@@ -17,6 +17,10 @@
 
 import Common
 
+public struct ExpressionStatement {
+  public init() {}
+}
+
 public struct Program {
     public var types: [P4Type] = Array()
 
@@ -29,7 +33,6 @@ public struct Program {
 
     public func find_parser(withName name: Identifier) -> Result<Parser> {
         for type in self.types {
-            print("type: \(type)")
             guard let parser = type as? Parser else {
                 continue
             }

Sources/Parser/Expression.swift

@@ -0,0 +1,109 @@
+// 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/>.
+
+// expression: $ => choice($.identifier, $.integer, $.true, $.false, $.string_literal), // Very limited.
+
+import Common
+import SwiftTreeSitter
+import TreeSitterP4
+
+protocol ParseableEvaluatableExpression {
+  static func parse(node: Node, inTree tree: MutableTree) -> Result<EvaluatableExpression?>
+}
+
+extension Identifier: ParseableEvaluatableExpression {
+  static func parse(
+    node: SwiftTreeSitter.Node, inTree tree: SwiftTreeSitter.MutableTree
+  ) -> Result<EvaluatableExpression?> {
+
+    guard
+      let parser_statement_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (identifier) @identifier)"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let qr = parser_statement_query.execute(node: node, in: tree)
+
+    guard let result = qr.next() else {
+      return .Ok(.none)
+    }
+
+    return .Ok(Identifier(name: result.captures[0].node.text!))
+  }
+}
+
+extension P4BooleanValue: ParseableEvaluatableExpression {
+  static func parse(
+    node: SwiftTreeSitter.Node, inTree tree: SwiftTreeSitter.MutableTree
+  ) -> Result<EvaluatableExpression?> {
+
+    guard
+      let true_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (true))"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let true_qr = true_query.execute(node: node, in: tree)
+
+    if true_qr.next() != nil {
+      return .Ok(P4BooleanValue(withValue: true))
+    }
+
+    guard
+      let false_query = try? SwiftTreeSitter.Query(
+        language: p4lang,
+        data: String(
+          "(expression (false))"
+        ).data(using: String.Encoding.utf8)!)
+    else {
+      return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+    }
+
+    let false_qr = false_query.execute(node: node, in: tree)
+
+    if false_qr.next() != nil {
+      return .Ok(P4BooleanValue(withValue: false))
+    }
+    return .Ok(.none)
+  }
+}
+
+struct Expression {
+  public static func Parse(node: Node, inTree: MutableTree) -> Result<EvaluatableExpression> {
+    let localElementsParsers: [ParseableEvaluatableExpression.Type] = [
+      P4BooleanValue.self, Identifier.self,
+    ]
+
+    for le_parser in localElementsParsers {
+      if case Result.Ok(.some(let parsed)) = le_parser.parse(
+        node: node, inTree: inTree)
+      {
+        return .Ok(parsed)
+      }
+    }
+
+    return Result.Error(Error(withMessage: "Could not parse into expression."))
+  }
+}

Sources/Parser/Parser.swift

@@ -229,10 +229,95 @@ public struct Parser {
       return Result.Ok(statements)
     }
 
+    static func TransitionKeysetExpression(
+      node: Node, inTree tree: MutableTree
+    ) -> Result<[KeysetExpression]> {
+      guard
+        let transition_selection_expression_query = try? SwiftTreeSitter.Query(
+          language: p4lang,
+          data: String(
+            "((keysetExpression (expression) @ks) (colon) (identifier) @next-state)"
+          ).data(using: String.Encoding.utf8)!)
+      else {
+        return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+      }
+
+      let qr = transition_selection_expression_query.execute(node: node, in: tree)
+
+      var kses: [KeysetExpression] = Array()
+
+      for expression in qr {
+        let next_state_name = expression.captures[1].node.text!
+        if case .Error(let e) = Expression.Parse(node: expression.captures[0].node, inTree: tree)
+          .map(block: { expression in
+            kses.append(
+              KeysetExpression(
+                withKey: expression, withNextStateName: next_state_name))
+            return .Ok(expression)
+          })
+        {
+          return .Error(e)
+        }
+      }
+
+      return .Ok(kses)
+    }
+
+    static func TransitionSelectExpression(
+      node: Node, inTree tree: MutableTree
+    ) -> Result<ParserTransitionStatement> {
+      guard
+        let transition_selection_expression_query = try? SwiftTreeSitter.Query(
+          language: p4lang,
+          data: String(
+            "(parserTransitionStatement (transition) (transitionSelectionExpression (selectExpression (select) (expression) @selector (selectBody) @body)))"
+          ).data(using: String.Encoding.utf8)!)
+      else {
+        return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+      }
+
+      let qr = transition_selection_expression_query.execute(node: node, in: tree)
+
+      guard let query_result = qr.next() else {
+        return .Error(Error(withMessage: "Could not find transition select expression"))
+      }
+
+      let selector = query_result.captures(named: "selector")
+      let body = query_result.captures(named: "body")
+
+      return Expression.Parse(node: selector[0].node, inTree: tree).map { expression in
+        return switch TransitionKeysetExpression(node: body[0].node, inTree: tree) {
+        case .Ok(let kse):
+          Result<ParserTransitionStatement>.Ok(
+            ParserTransitionStatement(
+              withTransitionExpression: ParserTransitionSelectExpression(
+                withSelector: expression, withKeysetExpressions: kse)))
+        case .Error(let e): Result<ParserTransitionStatement>.Error(e)
+        }
+      }
+    }
+
     static func TransitionStatement(
       node: Node, inTree tree: MutableTree
-    ) -> ParserTransitionStatement? {
+    ) -> Result<ParserTransitionStatement> {
-      return ParserTransitionStatement()
+      guard
+        let next_state_query = try? SwiftTreeSitter.Query(
+          language: p4lang,
+          data: String(
+            "(parserTransitionStatement (transition) (transitionSelectionExpression (identifier) @next-state))"
+          ).data(using: String.Encoding.utf8)!)
+      else {
+        return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
+      }
+
+      let qr = next_state_query.execute(node: node, in: tree)
+
+      if let next_state_result = qr.next() {
+        let transition_capture = next_state_result.captures(named: "next-state")
+        return .Ok(ParserTransitionStatement(withNextState: transition_capture[0].node.text!))
+      }
+
+      return TransitionSelectExpression(node: node, inTree: tree)
     }
 
     static func State(node: Node, inTree tree: MutableTree) -> Result<ParserState> {
@@ -259,7 +344,7 @@ public struct Parser {
       guard !state_name_capture.isEmpty,
         !transition_capture.isEmpty,
         let parsed_state_name = state_name_capture[0].node.text,
-        let transition_statement = TransitionStatement(
+        case .Ok(let transition_statement) = TransitionStatement(
           node: transition_capture[0].node, inTree: tree)
       else {
         return Result.Error(Error(withMessage: "Could not parse a parser declaration"))
@@ -297,7 +382,9 @@ public struct Parser {
           withTransition: transition_statement))
     }
   }
-  static func Parser(withName name: Identifier, node: Node, inTree tree: MutableTree) -> Result<Lang.Parser> {
+  static func Parser(
+    withName name: Identifier, node: Node, inTree tree: MutableTree
+  ) -> Result<Lang.Parser> {
     guard
       let parser_state_query = try? SwiftTreeSitter.Query(
         language: p4lang,
@@ -312,12 +399,23 @@ public struct Parser {
     var parser = Lang.Parser(withName: name)
 
     // Build a state from each one listed.
-    for parser_states in parser_state_query.execute(node: node, in: tree) {
+    let qr = parser_state_query.execute(node: node, in: tree)
-      switch P4Parser.State(node: parser_states.nodes[0], inTree: tree) {
+    let qr_value = qr.next()!
-      case Result.Ok(let state): parser.states.append(state)
+    let captures = qr_value.captures(named: "parser-states")
-      case Result.Error(let error): return Result.Error(error)
+
+    var error: Error? = .none
+
+    // TODO: Assert that there is only one.
+    captures[0].node.enumerateChildren { parser_state in
+      switch P4Parser.State(node: parser_state, inTree: tree) {
+      case Result.Ok(let state): parser.states = parser.states.append(state: state)
+      case Result.Error(let e): error = e
       }
     }
+
+    if let error = error {
+      return .Error(error)
+    }
     return Result.Ok(parser)
   }
 
@@ -354,7 +452,10 @@ public struct Parser {
     let parser_qc = parser_declaration_query.execute(in: tree)
 
     for parser_declaration in parser_qc {
-      switch Parser(withName: Identifier(name: parser_declaration.nodes[0].text!), node: parser_declaration.nodes[1], inTree: tree) {
+      switch Parser(
+        withName: Identifier(name: parser_declaration.nodes[0].text!),
+        node: parser_declaration.nodes[1], inTree: tree)
+      {
       case Result.Ok(let parser): program.types.append(parser)
       case Result.Error(let error): return Result.Error(error)
       }

Sources/Runtime/Parser.swift

@@ -18,16 +18,7 @@
 import Common
 import Lang
 
-
+extension ParserState: EvaluatableParserTransition {
-
-extension ParserTransitionStatement: EvaluatableParserTransitionStatement {
-  // TODO: Currently transitions to accept.
-  func transition(execution: ProgramExecution) -> (ParserState, ProgramExecution) {
-    return (accept, execution)
-  }
-}
-
-extension ParserState: EvaluatableParserState {
   public func evaluate(execution: ProgramExecution) -> (ParserState, ProgramExecution) {
     var currentExecution = execution
 
@@ -41,10 +32,34 @@ extension ParserState: EvaluatableParserState {
       currentExecution = statement.evaluate(execution: currentExecution)
     }
 
-    return if let transition = transition {
+    if direct_transition() {
-      transition.transition(execution: currentExecution)
+      return (next_state!, currentExecution)
-    } else {
-      (reject, currentExecution)
     }
+
+    if let transition_expression = self.transition,
+      let transition_select_expression = transition_expression.transition_expression
+    {
+      return transition_select_expression.evaluate(execution: currentExecution)
+    }
+    return (reject, currentExecution)
+  }
+}
+
+extension ParserTransitionSelectExpression: EvaluatableParserTransition {
+  func evaluate(execution: Common.ProgramExecution) -> (Lang.ParserState, Common.ProgramExecution) {
+    // First, evaluate the selector.
+
+    switch self.selector.evaluate(execution: execution) {
+    case .Ok(let selector_value):
+        for kse in self.keyset_expressions {
+          if case .Ok(let kse_key) = kse.key.evaluate(execution: execution),
+            kse_key.eq(rhs: selector_value)
+          {
+            return (kse.next_state!, execution)
+          }
+        }
+    case .Error(let e): return (reject, execution.setError(error: e))
+    }
+    return (reject, execution)
   }
 }

Sources/Runtime/Program.swift

@@ -31,3 +31,10 @@ extension ExpressionStatement: EvaluatableParserStatement {
     return execution
   }
 }
+
+// Variables are evaluatable because they can be looked up by identifiers.
+extension Identifier: EvaluatableExpression {
+    public func evaluate(execution: Common.ProgramExecution) -> Result<P4Value> {
+      return execution.scopes.evaluate(identifier: self)
+    }
+}

Sources/Runtime/Protocols.swift

@@ -18,7 +18,7 @@
 import Common
 import Lang
 
-protocol EvaluatableParserState {
+protocol EvaluatableParserTransition {
   func evaluate(execution: ProgramExecution) -> (ParserState, ProgramExecution)
 }
 

Sources/Runtime/Runtime.swift

@@ -20,14 +20,15 @@ import Lang
 
 /// The runtime for a parser
 public class ParserRuntime: CustomStringConvertible {
-  var execution: ParserInstance
+  var parser: ParserInstance
 
   init(execution: ParserInstance) {
-    self.execution = execution
+    self.parser = execution
   }
 
   /// Create a parser runtime from a P4 program
   public static func create(program: Lang.Program) -> Result<ParserRuntime> {
+
     return switch program.starting_parser() {
     case .Ok(let parser):
       switch ParserInstance.create(parser) {
@@ -40,12 +41,12 @@ public class ParserRuntime: CustomStringConvertible {
 
   /// Run the P4 parser on a given packet
   public func run(input: Packet) -> Result<(ParserState, ProgramExecution)> {
-    execution.scopes.enter()
+    parser.scopes.enter()
-    return .Ok(execution.execute())
+    return .Ok(parser.execute())
   }
 
   public var description: String {
-    return "Runtime:\nExecution: \(execution)"
+    return "Runtime:\nExecution: \(parser)"
   }
 }
 
@@ -57,7 +58,7 @@ extension ParserInstance: Execution {
 
     // Evaluate until the state is either accept or reject.
     while state != accept && state != reject {
-      (state, execution) = self.state.evaluate(execution: execution)
+      (state, execution) = state.evaluate(execution: execution)
     }
     return (state, execution)
   }

Tests/p4rseTests/ParserTests.swift

@@ -15,15 +15,14 @@
 // 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 Runtime
+import SwiftTreeSitter
 import Testing
 import TreeSitter
-import SwiftTreeSitter
 import TreeSitterP4
-import Foundation
-import Runtime
-import Common
-
-import Macros
 
 @testable import Parser
 
@@ -31,7 +30,7 @@ import Macros
   let simple_parser_declaration = """
     parser main_parser() {
        state start {
-               transition drop;
+           transition start;
        }
     };
     """
@@ -39,20 +38,28 @@ import Macros
   let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
   let parser = try #UseOkResult(program.find_parser(withName: Identifier(name: "main_parser")))
 
-    #expect(parser.states.count == 1)
+  #expect(parser.states.count() == 1)
-    #expect(parser.states[0].state_name == "start")
+  let state = try! #require(parser.states.find(withName: "start"))
-    #expect(parser.states[0].statements.count == 0)
+  #expect(state.state_name == "start")
+  #expect(state.statements.count == 0)
+
+  #expect(#RequireOkResult(parser.states.semantic_check()))
+  let next_state = try! #require(state.next_state)
+  #expect(next_state == state)
 }
 
 @Test func test_simple_parser_syntax_error() async throws {
   let simple_parser_declaration = """
     parser main_parser() {
        state
-               transition drop;
+           transition start;
        }
     };
     """
-    #expect(#RequireErrorResult(Error(withMessage: "Could not compile the P4 program"), Parser.Program(simple_parser_declaration)))
+  #expect(
+    #RequireErrorResult(
+      Error(withMessage: "Could not compile the P4 program"),
+      Parser.Program(simple_parser_declaration)))
 }
 
 @Test func test_simple_parser_with_statement() async throws {
@@ -60,7 +67,7 @@ import Macros
     parser main_parser() {
        state start {
            true;
-               transition drop;
+           transition start;
        }
     };
     """
@@ -68,9 +75,11 @@ import Macros
   let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
   let parser = try #UseOkResult(program.find_parser(withName: Identifier(name: "main_parser")))
 
-    #expect(parser.states.count == 1)
+  #expect(parser.states.count() == 1)
-    #expect(parser.states[0].state_name == "start")
+
-    #expect(parser.states[0].statements.count == 1)
+  let state = try! #require(parser.states.find(withName: "start"))
+  #expect(state.state_name == "start")
+  #expect(state.statements.count == 1)
 }
 
 @Test func test_simple_parser_with_instantiation() async throws {
@@ -78,17 +87,12 @@ import Macros
     parser main_parser() {
        state start {
            true;
-               transition drop;
+           transition start;
        }
     };
     bool() main;
     """
 
   let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
-
+  #expect(#RequireOkResult(program.find_parser(withName: Identifier(name: "main_parser"))))
-    let parser = try #UseOkResult(program.find_parser(withName: Identifier(name: "main_parser")))
-    #expect(parser.states.count == 1)
-    #expect(parser.states[0].state_name == "start")
-    #expect(parser.states[0].statements.count == 1)
 }
-

Tests/p4rseTests/RuntimeTests.swift

@@ -28,6 +28,30 @@ import TreeSitterP4
 @testable import Parser
 
 @Test func test_simple_runtime() async throws {
+  let simple_parser_declaration = """
+    parser main_parser() {
+       state start {
+           true;
+           transition accept;
+       }
+    };
+    """
+
+  let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
+  #expect(#RequireOkResult(Runtime.ParserRuntime.create(program: program)))
+
+  let runtime = try #UseOkResult(Runtime.ParserRuntime.create(program: program))
+
+  guard case Common.Result.Ok(let (state_result, _)) = runtime.run(input: Packet())
+  else {
+    assert(false)
+  }
+
+  // We should be in the accept state.
+  #expect(state_result == Lang.accept)
+}
+
+@Test func test_simple_runtime_to_accept() async throws {
   let simple_parser_declaration = """
     parser main_parser() {
        state start {
@@ -39,8 +63,19 @@ import TreeSitterP4
 
   let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
   #expect(#RequireOkResult(Runtime.ParserRuntime.create(program: program)))
+
+  let runtime = try #UseOkResult(Runtime.ParserRuntime.create(program: program))
+
+  guard case Common.Result.Ok(let (state_result, _)) = runtime.run(input: Packet())
+  else {
+    assert(false)
+  }
+
+  // We should be in the accept state.
+  #expect(state_result == Lang.reject)
 }
 
+
 @Test func test_simple_runtime_no_start_state() async throws {
   let simple_parser_declaration = """
     parser main_parser() {
@@ -89,7 +124,7 @@ import TreeSitterP4
   }
 
   // We should be in the accept state.
-  #expect(state_result == Lang.accept)
+  #expect(state_result == Lang.reject)
 
   // There are two variables declared.
   #expect(scope.count == 2)
@@ -100,3 +135,57 @@ import TreeSitterP4
   #expect(b.value_type.eq(rhs: P4BooleanValue(withValue: false)))
   #expect(s.value_type.eq(rhs: P4StringValue(withValue: "\"testing\"")))
 }
+
+@Test func test_simple_parser_with_transition_select_expression() async throws {
+  let simple_parser_declaration = """
+      parser main_parser() {
+        state start {
+          transition select (true) {
+            false: reject;
+            true: accept;
+          };
+        }
+      };
+    """
+
+  let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
+  #expect(#RequireOkResult(program.find_parser(withName: Identifier(name: "main_parser"))))
+  let parser = try #UseOkResult(program.find_parser(withName: Identifier(name: "main_parser")))
+
+  #expect(parser.states.count() == 1)
+
+  let runtime = try #UseOkResult(Runtime.ParserRuntime.create(program: program))
+
+  guard case Common.Result.Ok(let (state_result, _)) = runtime.run(input: Packet())
+  else {
+    assert(false)
+  }
+  #expect(state_result == Lang.accept)
+}
+
+@Test func test_simple_parser_with_transition_select_expression_to_reject() async throws {
+  let simple_parser_declaration = """
+      parser main_parser() {
+        state start {
+          transition select (false) {
+            false: reject;
+            true: accept;
+          };
+        }
+      };
+    """
+
+  let program = try #UseOkResult(Parser.Program(simple_parser_declaration))
+  #expect(#RequireOkResult(program.find_parser(withName: Identifier(name: "main_parser"))))
+  let parser = try #UseOkResult(program.find_parser(withName: Identifier(name: "main_parser")))
+
+  #expect(parser.states.count() == 1)
+
+  let runtime = try #UseOkResult(Runtime.ParserRuntime.create(program: program))
+
+  guard case Common.Result.Ok(let (state_result, _)) = runtime.run(input: Packet())
+  else {
+    assert(false)
+  }
+  #expect(state_result == Lang.reject)
+}