Error – Io

An object that contains error information and flow control based on errors. ifError(code)

Evaluates code in the context of sender. Returns self.
Another form is Error ifError(error, code). Note: error slot is set in the context of sender, Locals object is not created!

isError

Returns true.

raiseIfError

Raises exception.

returnIfError

Returns self from the context of sender.

with(message)

Returns new error with message slot set.