witchcrafters/algae

`flat_map/2` is needed

dobashi opened this issue · 2 comments

dobashi commented

I wanna use Either/Maybe with flat_map function like this.

    func1(2)
    |> flat_map(& func2(&1))
    |> flat_map(& func3(&1))

All functions return Either.Right|Left. I defined flat_map/2 in my project.

defp flat_map(%Right{right: x}, f), do: f.(x)
defp flat_map(%Left{left: x}, f), do: x

But I think Either/Maybe have to define definst ... def flat_map(). I tried to add flat_map to Witchcraft.Functor and define then in Algae.Either but it occurs an error.

== Compilation error in file lib/algae/either.ex ==
** (UndefinedFunctionError) function Witchcraft.Functor.Proto.Algae.Either.Left.map/2 is undefined or private, but the behaviour Witchcraft.Functor.Proto expects it to be present
    Witchcraft.Functor.Proto.Algae.Either.Left.map(%Algae.Either.Left{left: [266, <<29, 23, 14, 62>>, -1.7183673469387755, <<48, 56, 69, 24>>]}, #Function<2.93944398/1 in Witchcraft.Functor.Property.composition/1>)

Does anyone have an idea to add flat_map/2 to Either|Maybe?

hariroshan commented

you don't have to define your own functions. flat_map/2 is same as bind/2 or chain/2 which is defined in Witchcraft.Chain. Most of the functions are already defined in Witchcraft.

simply look read the witchcraft docs.

example


>> import Witchcraft.Chain
>> Algae.Either.Right.new(100) |> bind(& Algae.Either.Right.new(&1 + 10))
>> %Algae.Either.Right{right: 110}
dobashi commented

Oh I see. You're right. Sorry for late reply.

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