Open union error type - Polysemy

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Open union error type
Sridhar Ratnakumar
2020-05-08 13:00:45

When using polysemy, do we have any special privilege to be able to straightforwardly define open union error types?

In other words, is MultiError easy to implement?

doSomething
  :: Members '[SomeEffect, MultiError '[ParseError, RenderError]] m
  => m a

cf. https://funprog.srid.ca/haskell/either-type-level-list.html

Either type-level list - Haskell
Using Either as a type operator makes the signature more palatable for nested Eithers: parse :: String -> Foo `Either` Bar `Either` Baz parse = undefined But writing Right (Left bar) is pretty janky. Can that be improved as well?
Georgi Lyubenov // googleson78
2020-05-08 13:06:56

with Polysemy I've just used multiple Error effects instead

Torsten Schmits
2020-05-08 13:10:43

with semantics being that you have to handle them all at the same time? or runError returning a tuple?

Georgi Lyubenov // googleson78
2020-05-08 13:11:43

I guess you could use Bundle to stack Errors with some success

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