[Haskell-cafe] Why is the no tuple syntax for sum types

[Phil Ruffwind]

For sum types you need a way to construct them and pattern match them.
Without a way to _name_ them, it would probably look like this:

    showError :: (Result | Error3 | Error8) -> String
    showError (result ||)   = "no error"
    showError (| error3 |)  = "error3: " ++ show error3
    showError (|| error8 |) = "error8: " ++ show error8

It's not the most readable code, so I'd generally avoid using it for
anything greater than 3 (same applies to tuples).

It also suffers the same flaw as tuples: no way to extend them easily.
Imagine adding a new error: you have to edit _all_ of the patterns:

    showError :: (Result | Error3 | Error8 | Error11 ) -> String
    showError (result |||)   = "no error"
    showError (| error3 ||)  = "error3: "  ++ show error3
    showError (|| error8 |)  = "error8: "  ++ show error8
    showError (||| error11 ) = "error11: " ++ show error11

Extensible records and variants might be able to solve these problems,
but that's a rabbit-hole of its own though.