[Haskell-cafe] Why does Haskell have both `Maybe a` and `Either a ()`?

Wiebe-Marten Wijnja w-m at wmcode.nl
Fri May 29 10:24:40 UTC 2020


Greetings, everyone!

Recently I was involved in a discussion on the new ML-style language
'gleam'.

Gleam has for quite a while now only had an `Either a b` type,
with all functions that in Haskell one would use a `Maybe a` for,
working on an `Either a ()` instead.

In the discussion(https://github.com/gleam-lang/gleam/issues/591), the
language designers were asking the community whether it would make sense
to add `Maybe` to the language as well,
or keep using only `Either a ()`.


My question: Is the difference between `Maybe a` and `Either a ()` only
semantic and are they functionally equivalent,
or are there differences in functionality as well?


Have a nice day,

~Marten / Qqwy


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