Davi Sales Barreira (Aug 08 2023 at 11:52): Davi Sales Barreira (Aug 08 2023 at 11:52):Hello, friends. I have recently learned of something called a Free Monad, which is similar to a list, but over functors. I was wondering how this could be implemented in Julia. In Haskell, a free monad is defined as
data Free f a = Pure a | Free (f (Free f a))
This Free f takes a functor f and creates a new functor (e.g. Free_f) which has a monadic structure.
I'm having a hard time figuring out how to implement this in Julia, specifically due to this recrusive nature of the definition.
I was wondering if anyone with expirience in functional programming could help.
Alec (Aug 08 2023 at 19:33):Maybe this might help, or at least the rest of the page? https://github.com/Moelf/functional-programming-jargon.jl#monad
Alec (Aug 08 2023 at 19:33):I’m a beginner at best at this sort of thing so apologies if not helpful
Davi Sales Barreira (Aug 08 2023 at 23:04):Thanks @Alec . Ive seen this, but not really helpful in this situation :(
Sukera (Aug 09 2023 at 12:54):implementing a functor in Julia is implementing map(f, x::T) -> T for your T, if I'm not mistaken
Sukera (Aug 09 2023 at 12:54):since "functor" in haskell just means "mappable"
Sukera (Aug 09 2023 at 12:55):the important thing is that structure is preserved; if your T is a tree, you'll get a tree with the same structure back out
Sukera (Aug 09 2023 at 12:56):what Free then does is destroy that structure - instead of a tree, you'd get a flat list back out; hence why it's sometimes called flatmap
Sukera (Aug 09 2023 at 12:56):I think the closest analog we have is collect after such a map over a functor
Sukera (Aug 09 2023 at 12:57):(it's a bit confusing that we call callables functors in julia...)
Davi Sales Barreira (Aug 09 2023 at 13:40):I think I was able to implement a working example of an instance of FreeF. The actual Free functor that turns functors F into FreeF can perhaps be done via macros.
Davi Sales Barreira (Aug 09 2023 at 13:41):I call parametric struct functors when they have an fmap function. I think this is how they do in Functors.jl
Sukera (Aug 09 2023 at 18:54):Yes, that's pretty much the same thing, except applied to a whole struct (which is not necessary in general; you can have "mappable structure" without mapping over every field of an object)
Sukera (Aug 09 2023 at 18:56):ah, Functors.jl supports that too
Sukera (Aug 09 2023 at 18:56):yeah, it's unrelated to being parametrized or not :)
Sundar R (Aug 10 2023 at 20:55):I'm a complete novice here, but I came across Effects.jl on my github feed recently by coincidence. Its readme says:
An implementation of effect handlers in Julia (aka algebraic effects, free monads etc).
I know some of those words :smile: but no idea if this is helpful either
Davi Sales Barreira (Aug 11 2023 at 10:44):Thanks, a lot @Sundar R !
Alexander (Aug 12 2023 at 09:34):See also optics, as implemented in Accessors.jl: they allow both traversing and modifying a structure (flat or nested), or extracting all/specified elements as a flat list, or putting such a list of elements back into the original structure.
Last updated: Oct 02 2023 at 04:34 UTC