Assets/Scripts/enemy.cs(19,35): error CS1612: Cannot modify a value type return value of `UnityEngine.Transform.position’. Consider storing the value in a temporary variable.
C# and Boo don’t accept changes to single components of properties: you must copy to a variable, change the component and save it back:
Vector3 temp = transform.position; // copy to an auxiliary variable...
temp.y = 7.0f; // modify the component you want in the variable...
transform.position = temp; // and save the modified value