Error Handlers

Error Handlers

By error handlers I mean those operators that do for errors — meaning failures — what operators such as .map and .filter do for values. Both values and failures are objects that come down the pipeline, and each has a type; and just as you can transform one value into another, and even into a different type of value, or prevent a value from moving further down the pipeline, it is perfectly reasonable to want to do the same sort of thing for failures.

The error handler par excellence is .mapError, which does just what .map does, but for errors: if it receives a failure from upstream, it can send downstream a failure containing a different error object, even a different type of error object.