/// <summary>
/// References a variable. Searches the enclosing environment if not found.
/// Signals an error if the variable is unbound.
/// </summary>
/// <param name="key">The name of the variable.</param>
/// <returns></returns>
public IValue LookupBinding(string key)
{
if (this == TheEmptyEnvironment)
{
throw new RuntimeErrorException("environment", $"Attempting to reference an unbound variable '{key}");
}
if (bindings.ContainsKey(key))
{
return(bindings[key]);
}
else
{
return(EnclosingEnvironment.LookupBinding(key));
}
}
/// <summary>
/// Assigns to a variable. Searches the enclosing environment if not found.
/// Signals an error if the variable is unbound.
/// </summary>
/// <param name="key">The name of the variable.</param>
/// <param name="newValue">The new value of the variable</param>
public void SetBinding(string key, IValue newValue)
{
if (this == TheEmptyEnvironment)
{
throw new RuntimeErrorException("environment", $" Attempting to assign to an unbound variable '{key}");
}
if (bindings.ContainsKey(key))
{
bindings[key] = newValue;
}
else
{
EnclosingEnvironment.SetBinding(key, newValue);
}
}
