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 {