Functional Semantics in Imperative Clothing (Richard Feldman)

Re:Functional Semantics in Imperative Clothing (Richard Feld... by rtfeldman on Monday April 29, 2024 @10:30AM (#40198783)

Roc actually doesn't use algebraic effects under the hood, although errors can naturally accumulate in a way that makes the code look more like error handling in algebraic effects systems:

https://www.roc-lang.org/tutorial#task-failure

The implementation detail that makes this error handling possible is that Roc uses anonymous sum types called "tags" (OCaml calls them polymorphic variants) that can accumulate on the fly:

https://www.roc-lang.org/tutorial#tags

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Re:Functional Semantics in Imperative Clothing (Richard Feld... by tkz1312 on Monday April 29, 2024 @11:06AM (#40199276)

Very interesting, thanks for the clarification. What is the difference between algebraic effects and rocs approach?

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Re:Functional Semantics in Imperative Clothing (Richard Feld... by rtfeldman on Monday April 29, 2024 @11:23AM (#40199527)

In Haskell terms, Roc's `Task ok err` is essentially an `IO (Either err ok)` - the only difference between how Roc does it and how Haskell does it is that `Task` bakes in error handling whereas `IO` doesn't. (Plus the syntax sugar being different, of course.)

So the biggest difference is that algebraic effects are a separate language feature, whereas Task (like IO in Haskell) is a plain old type in the standard library that happens to represent effeects.

Incidentally, the Task.await function in Roc is based on Elm's Task.andThen - we just tried out a different name and argument order for it:

https://package.elm-lang.org/packages/elm/core/latest/Task#a...

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