C#•17mo ago

✅ LanguageExt bind if

I'm having trouble understanding how to do something particular in LanguageExt that I think is just a part of functional programming in general. I have an effectful method, which I then want to evaluate the result of, and rerun if not meeting a condition. Originally, I did it like this

var key = PollInput<RT>();
        
return key.Bind(pressedKey => pressedKey.Match(
    Left: keys.Contains,
    Right: _ => true)
    ? key
    : IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys)));

var key = PollInput<RT>();
        
return key.Bind(pressedKey => pressedKey.Match(
    Left: keys.Contains,
    Right: _ => true)
    ? key
    : IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys)));

Turns out, obviously enough, it runs PollInput twice when you do this, which isn't good. Instead, I'm now trying to do something like this

from keyPressed in PollInput<RT>()
from _ in keyPressed.Match(
    Left: keys.Contains,
    Right: _ => true)
    ? keyPressed
    : IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys));

from keyPressed in PollInput<RT>()
from _ in keyPressed.Match(
    Left: keys.Contains,
    Right: _ => true)
    ? keyPressed
    : IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys));

But this doesn't work, since keyPressed is not an Eff, and PollValidInput (the method this is running in), is an Eff. I have no idea how to do this. I just want to bind that else condition when that match fails, but I need to bind/map to run that condition, so I also need to return something for when that condition is met. Any ideas?

1 Reply

LukeJ•17mo ago

Figured it out

PollInput<RT>()
    .Where(keyPressed => keyPressed.Match(
        Left: keys.Contains,
        Right: _ => true))
    .IfFailEff(IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys)));

PollInput<RT>()
    .Where(keyPressed => keyPressed.Match(
        Left: keys.Contains,
        Right: _ => true))
    .IfFailEff(IO<RT>.ClearCharacter()
        .Bind(_ => PollValidInput<RT>(keys)));

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✅ LanguageExt bind if