parser, compiler: Support Table Actions

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

Sources/P4Compiler/Walker.swift

@@ -51,4 +51,21 @@ public struct Walker {
     }
     return Result.Ok(())
   }
+
+  public func try_map<T>(n: Int, onlyNamed: Bool = false, todo: (Node) -> Result<T>) -> ([T], [Error]) {
+    var errors: [Error] = Array()
+    var results: [T] = Array()
+
+    for currentChildIdx in currentChildIdx..<n {
+      let currentChild = node.child(at: currentChildIdx)!
+      if onlyNamed && !currentChild.isNamed {
+        continue
+      }
+      switch todo(currentChild) {
+        case .Ok(let r): results.append(r)
+        case .Error(let e): errors.append(e)
+      }
+    }
+    return (results, errors)
+  }
 }