diff --git a/Sources/Common/ProgramTypes.swift b/Sources/Common/ProgramTypes.swift
index bc9dbd2..faf45ca 100644
--- a/Sources/Common/ProgramTypes.swift
+++ b/Sources/Common/ProgramTypes.swift
@@ -158,6 +158,10 @@ public struct P4Struct: P4Type {
       false
     }
   }
+
+  public func def() -> any P4Value {
+    return P4StructValue(withType: self)
+  }
 }
 
 /// An instance of a P4 struct
@@ -231,6 +235,9 @@ public struct P4Boolean: P4Type {
     default: false
     }
   }
+  public func def() -> any P4Value {
+    return P4BooleanValue(withValue: false)
+  }
 }
 
 /// An instance of a P4 boolean
@@ -269,6 +276,9 @@ public struct P4Int: P4Type {
     default: false
     }
   }
+  public func def() -> any P4Value {
+    return P4IntValue(withValue: 0)
+  }
 }
 
 /// An instance of a P4 integer
@@ -309,6 +319,9 @@ public struct P4String: P4Type {
     default: false
     }
   }
+  public func def() -> any P4Value {
+    return P4StringValue(withValue: "")
+  }
 }
 /// An instance of a P4 string
 public class P4StringValue: P4Value {
@@ -358,6 +371,10 @@ public struct P4Array: P4Type {
     default: false
     }
   }
+
+  public func def() -> P4Value {
+    return P4ArrayValue(withType: self, withValue: [])
+  }
 }
 
 /// An instance of a P4 array
diff --git a/Sources/Common/Protocols.swift b/Sources/Common/Protocols.swift
index affbe3e..89acb0f 100644
--- a/Sources/Common/Protocols.swift
+++ b/Sources/Common/Protocols.swift
@@ -34,14 +34,21 @@ public protocol EvaluatableStatement {
 
 public protocol P4Type: CustomStringConvertible {
   func eq(rhs: any P4Type) -> Bool
+  func def() -> P4Value
 }
 
-public protocol P4Value: CustomStringConvertible {
+public protocol P4Value: EvaluatableExpression, CustomStringConvertible {
   func type() -> any P4Type
   func eq(rhs: P4Value) -> Bool
 }
 
-public protocol EvaluatableLValueExpression: EvaluatableExpression {
-  func set(to: P4Value, inScopes scopes: ValueScopes, duringExecution execution: ProgramExecution) -> Result<(ValueScopes, P4Value)>
-  func check(to: EvaluatableExpression, inScopes scopes: TypeScopes) -> Result<()>
+public extension P4Value {
+  func evaluate(execution: ProgramExecution) -> Result<P4Value> {
+    return Result.Ok(self)
+  }
+}
+
+public protocol EvaluatableLValueExpression: EvaluatableExpression {
+  func set(to: P4Value, inScopes scopes: VarValueScopes, duringExecution execution: ProgramExecution) -> Result<(VarValueScopes, P4Value)>
+  func check(to: EvaluatableExpression, inScopes scopes: VarTypeScopes) -> Result<()>
 }
diff --git a/Sources/P4Lang/Parser.swift b/Sources/P4Lang/Parser.swift
index 99101e6..d252cc9 100644
--- a/Sources/P4Lang/Parser.swift
+++ b/Sources/P4Lang/Parser.swift
@@ -83,6 +83,10 @@ public class ParserState: P4Type, P4Value, Equatable, CustomStringConvertible {
     state = name
     statements = Array()
   }
+
+  public func def() -> any P4Value {
+    return ParserState(name: Identifier(name: ""))
+  }
 }
 
 public class ParserStateDirectTransition: ParserState {
@@ -211,4 +215,8 @@ public struct Parser: P4Type, P4Value {
   public var description: String {
     return "Parser"
   }
+
+  public func def() -> any P4Value {
+    return Parser(withName: Identifier(name: ""))
+  }
 }