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> Monads with do-notation Phrased like this, it sounds like 'the monad abstraction' and 'good syntax for monads' are what helps, which is slightly off the mark

by mrkeen 3y ago

> Monads with do-notation Phrased like this, it sounds like 'the monad abstraction' and 'good syntax for monads' are what helps, which is slightly off the mark. But particular monads do help: - The Par monad gives you deterministic parallelism for computations. - The flipside of marking mutable/non-determistic functions as IO (another monad), is that the functions not marked as such are deterministic, non-interfering etc., so interleaving them differently will not grow the state-space. - The STM monad gives you transactions, which give you safe, shared mutability without running into the following issue from the article: > I can use programming constructs like mutexes and barriers to "prune" the state space and give me the behaviors I want, but given how big the state space can be, I have to do a lot of pruning to get the right behaviors. I can make mistakes in implementation, "misshape" the space (like by adding a deadlock), or not notice a buggy state I need to remove. Threads are very error prone. I'm not sure what 'Atoms' refer to, unless it's running code in an atomic block in STM. That said, having a good monadic syntax is still great, even if the syntax can't solve semantic concurrency issues. I believe that CompletableFutures were a good way to model async code in Java (and Rx/observables etc, to some extent). But they got resistance from Java programmers who didn't want to flatMap everything all the time. They had semantic issues too (can't cancel?!? what?!). But I think it's largely their syntax that made programmers miss the Thread model of writing straight-line imperative code.

cess11 3y ago
By atoms they might mean runtime-wide symbols that evaluate to themselves, kinda like a singleton that evaluates to itself. Useful for tagging data or states, in BEAM-languages like Erlang or Elixir you commonly use the atoms :ok and :error to tag tuples to make it easy to switch or pattern match into appropriate receiving branches. You'll also come across them in Lisp-like languages and logic programming. Edit: Another, maybe better, illustration from the BEAM might be the 'booleans', they're implemented as the atoms :true and :false.
saurik 3y ago
> Phrased like this, it sounds like 'the monad abstraction' and 'good syntax for monads' are what helps, which is slightly off the mark. > But particular monads do help: The part the language needs to provide are merely the abstraction and the good syntax which uses it, not the particular monads: you can then implement them as required.

by mrkeen 3y ago

cess11 3y ago

By atoms they might mean runtime-wide symbols that evaluate to themselves, kinda like a singleton that evaluates to itself. Useful for tagging data or states, in BEAM-languages like Erlang or Elixir you commonly use the atoms :ok and :error to tag tuples to make it easy to switch or pattern match into appropriate receiving branches. You'll also come across them in Lisp-like languages and logic programming. Edit: Another, maybe better, illustration from the BEAM might be the 'booleans', they're implemented as the atoms :true and :false.

saurik 3y ago

> Phrased like this, it sounds like 'the monad abstraction' and 'good syntax for monads' are what helps, which is slightly off the mark. > But particular monads do help: The part the language needs to provide are merely the abstraction and the good syntax which uses it, not the particular monads: you can then implement them as required.