What would be the maybe monad for crystal. Here for other languages, http://www.rosettacode.org/wiki/Monads/Maybe_monad

Unless I’m misunderstanding what the Maybe Monad is, Crystal uses Nil unions for this. For example, the return type of Array(T)#min? is T | Nil (which is the same as T?) because there’s no minimum if the Array is empty. So, in that case, T | Nil is the same as a hypothetical type Maybe(T).

Exactly. In Crystal map is Object#try. As an example, the code presented in the rosettacode for Ruby: class Maybe def initialize(value) @value = value end def map if @value.nil? self else Maybe.new(yield @value) end end end Maybe.new(3).map { |n| 2*n }.map { |…

@Alain , since you brought the topic, do you want to post the example in rosettacode? (I’ll do it otherwise).

If you do, post the link and I’ll include it in the Rosetta Code list. :smiley: [image] Improve Crystal's profile on Rosetta Code Community There are a lot of code categories on Rosetta code with no Crystal examples. https://rosettacode.org/wiki/Reports:Tasks_not_impleme…

A real Maybe ensures that Just and None are always disjoint, so Maybe(T) = T | Nil doesn’t suffice as T is nilable. A real implementation might be: record Just(T), value : T record None # alias Maybe(T) = Just(T) | None module Enumerable(T) def find2(& : T ->) : Just(T) | None each do |elem|…

Fair enough, but if you stack up Maybes, in most cases you don’t care where the None comes from (otherwise, you’ll use a more informative monad).

Maybe monad for crystal

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jzakiya July 25, 2022, 11:41pm 5

If you do, post the link and I’ll include it in the Rosetta Code list.

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Maybe monad for crystal

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