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Joined 1 year ago
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Cake day: June 19th, 2023

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  • In Maybe monadic, its monadic bind will automatically resolves any failed computation, and don’t need explicit checking.

    for example, the code in Haskell looks something like the following:

    fib: Int -> Int -> Maybe Int
    fib depth idx =
      do
         guard (depth < 10)
         n1 <- fib (depth - 1) (idx - 1)
         n2 <- fib (depth - 1) (idx - 2)
         return (n1 + n2)
    

    Haskell type class system automatically figures out this is a maybe monad, and check for error accordingly.

    Notice, unlike the C code the author provide, this haskell code will exit immediately when n1 failed and never compute n2, similar to the behavior of the exception code. Thus I believe his point about performance is at least unjustified, if not wrong.

    Another interesting fact about this code is that there is nothing that is built into the compiler/interpretor (except the do expression, which is just a minor syntactical sugar), you don’t need to design special semantics for raise and catch. Everything here, guard, return and the definition of Maybe monad (which is in charge of propagating errors) is defibed by the user using normal functions, no metaprogramming involved.

    Wouldn’t effect systems still be considered exceptions, but handled differently?

    Yes, unlike monad, the error is propagated by the compiler/interpretor, instead of user defined. But unlike implicit effect, explicit effect (algebraic effect, throwable, etc.) makes it clear how the code can go wrong.

    Although explicit error is more clear in general, there are special cases where explicit effect is undesirable. One such example is effect pollution, where low level effect that is unlikely to cause impure behavior is necessarily propgated through the call stack. Making the code more verbose and harder to handle.


  • The more I read about these kind of article the more I am amazed that our digital future is at hand in utterly incompetent people.

    This person clearly have no understanding of monadic error (AKA Maybe/option monad or slightly more advanced Either monad), which is the first monad we teach at a class targeting second year undergrad.

    The performance is just plain factual error. The functional error code will continue to compute n2 when computation of n1 failed; the same do not happen in the exception version. If you compare code with completely different trace, of course they will have different performance… A properly implemented monadic error will return as fast as compute for n1 failed, and never execute the rest. This is the default and idiomatic behavior for any properly implemented monad, like in haskell, ocaml, F#, and rust. This performance problem even shouldn’t happen in linq style handling like in C#, Kotlin (maybe Typescript?).

    The point of monadic error is that its control flow is local, whereas exception is non-local. Unless you have clear documentation about the possible error, then the return value is deceptive. And the error can be handled anywhere in the code base. And programmer knows non-local control flow (goto, break, contiune, exception, long jump) is the breeding ground for spaghetti code, so that many non-local control (goto, long jump) is baned in most languages.

    That being said, there are certainly cases, with proper documentation, the exception style is easy to write and understand. But I think they are specific scenarios that have to be justified on a case-by-case basis.