C#•2y ago

✅ Typed delegates in maps (LanguageExt)

Hello. I'm currently doing some functional programming with the LanguageExt package. I've been going through and adding an environment to my effectful methods, which has left me with a bit of a problem. I have 3 different turn methods that I store in in map, like so

private static readonly Map<ConsoleKey, TurnMethod> TurnMethodBinding = Map(
        (ConsoleKey.Z, (TurnMethod)UserTurn),
        (ConsoleKey.X, AITurn),
        (ConsoleKey.C, AITurnInPhases)
    );

private static readonly Map<ConsoleKey, TurnMethod> TurnMethodBinding = Map(
        (ConsoleKey.Z, (TurnMethod)UserTurn),
        (ConsoleKey.X, AITurn),
        (ConsoleKey.C, AITurnInPhases)
    );

This uses the delegate TurnMethod defined as

public delegate Eff<RT, Either<TurnReturn, ExitConsole>> TurnMethod<RT>(FieldState fieldState, User player) where RT : struct, HasIO<RT>;

public delegate Eff<RT, Either<TurnReturn, ExitConsole>> TurnMethod<RT>(FieldState fieldState, User player) where RT : struct, HasIO<RT>;

As you can see though, this is typed with RT, which got added to the signature when adding an environment to the method. This causes the Map problems, saying there's an incorrect number of type paramaters. I have no idea how to do that map with the type paramater included though. Any ideas?

10 Replies

Thinker•2y ago

Well, TurnMethod takes a single type parameter, but you're not giving it any in the map

LukeJOP•2y ago

Right, and I have no idea how I'd add a type parameter to it. I don't know what RT is at this point in the code, so if I understand right I'd need to add typing to the map itself, which I don't know how I'd do.

Thinker•2y ago

What is RT meant to be/do?

LukeJOP•2y ago

It's the runtime enviroment. So anything like IO that deals with the outside world which I can either have the proper function for, or a faked version for unit tests. Following this guide on it https://github.com/louthy/language-ext/wiki/How-to-deal-with-side-effects

Thinker•2y ago

I won't pretend I think LanuageEXT is very useful, abstracting IO like this is just unnecessary in C# imo

LukeJOP•2y ago

Function purity is pretty fundamental in FP. Practical or not, I gotta learn it for this project.

Thinker•2y ago

eh, arguable Anyway, you could probably specify the environment type as a type parameter on the class since that's a field

LukeJOP•2y ago

the class? As in the one housing all these methods?

Thinker•2y ago

ye the class containing the map

LukeJOP•2y ago

Hmm. That would work. I think it's really starting to get hacky at that point though. Sorta how LanguageExt goes a bit but still I think I might just replace the map with a method that has a switch.

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✅ Typed delegates in maps (LanguageExt)