Hello. As a personal learning exercise, I've been trying to see how far I could get with implementing functional programming concepts (my project's page is at github(dot)com/nothingnesses/rust-fp-library/tree/wip-traversable , but the forum won't let me add more than 2 links), but I've hit a wall trying to implement a traverse function for Vec. Here's the condensed code for my current attempt.
My issue is that I think I need to add some trait bound(s) to the relevant function signatures on the trait and in the implementing instances:
Compiling playground v0.0.1 (/playground)
error[E0277]: the trait bound `F: Kind1<A>` is not satisfied
--> src/lib.rs:717:7
|
717 | Apply<F, (A,)>,
| ^^^^^^^^^^^^^^ the trait `Kind1<A>` is not implemented for `F`
|
note: required for `F` to implement `Kind<(A,)>`
--> src/lib.rs:44:31
|
44 | impl<Brand, $($Generics),+> Kind<($($Generics,)+)> for Brand
| ^^^^^^^^^^^^^^^^^^^^^^ ^^^^^
45 | where
46 | Brand: $KindN<$($Generics),+>,
| ---------------------- unsatisfied trait bound introduced here
...
210 | make_trait_kind!(Kind1, Apply1, "* -> *", (A));
| ---------------------------------------------- in this macro invocation
= note: this error originates in the macro `make_trait_kind` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting type parameter `F` with trait `Kind1`
|
696 | F: 'a + Kind<(B,)> + Kind<(Apply<Self, (B,)>,)> + Applicative + Kind1<A>,
| ++++++++++
error[E0277]: the trait bound `F: Kind1<Arc<dyn Fn(<VecBrand as Kind<(A,)>>::Output) -> ...>>` is not satisfied
--> src/lib.rs:718:7
|
718 | Apply<F, (ClonableFn<'a, Apply<Self, (A,)>, Apply<Self, (A,)>>,)>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Kind1<Arc<(dyn Fn(<VecBrand as Kind<(A,)>>::Output) -> <VecBrand as Kind<(A,)>>::Output + 'a)>>` is not implemented for `F`
|
note: required for `F` to implement `Kind<(Arc<(dyn Fn(<VecBrand as Kind<(A,)>>::Output) -> <VecBrand as Kind<(A,)>>::Output + 'a)>,)>`
--> src/lib.rs:44:31
|
44 | impl<Brand, $($Generics),+> Kind<($($Generics,)+)> for Brand
| ^^^^^^^^^^^^^^^^^^^^^^ ^^^^^
45 | where
46 | Brand: $KindN<$($Generics),+>,
| ---------------------- unsatisfied trait bound introduced here
...
210 | make_trait_kind!(Kind1, Apply1, "* -> *", (A));
| ---------------------------------------------- in this macro invocation
= note: the full name for the type has been written to '/playground/target/debug/deps/playground-0397c81c81221729.long-type-1043842649665829542.txt'
= note: consider using `--verbose` to print the full type name to the console
= note: this error originates in the macro `make_trait_kind` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting type parameter `F` with trait `Kind1`
|
696 | F: 'a + Kind<(B,)> + Kind<(Apply<Self, (B,)>,)> + Applicative + Kind1<std::sync::Arc<(dyn std::ops::Fn(<VecBrand as Kind<(A,)>>::Output) -> <VecBrand as Kind<(A,)>>::Output + 'a)>>,
| ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
error[E0277]: the trait bound `F: Kind1<Arc<dyn Fn(<VecBrand as Kind<(B,)>>::Output) -> ...>>` is not satisfied
--> src/lib.rs:733:27
|
733 | let map_cons_f_head: Apply<
| __________________________________________^
734 | | F,
735 | | (ClonableFn<'a, Apply<Self, (B,)>, Apply<Self, (B,)>>,),
736 | | > = map_cons(f_head);
| |_____________________^ the trait `Kind1<Arc<(dyn Fn(<VecBrand as Kind<(B,)>>::Output) -> <VecBrand as Kind<(B,)>>::Output + 'a)>>` is not implemented for `F`
|
note: required for `F` to implement `Kind<(Arc<(dyn Fn(<VecBrand as Kind<(B,)>>::Output) -> <VecBrand as Kind<(B,)>>::Output + 'a)>,)>`
--> src/lib.rs:44:31
|
44 | impl<Brand, $($Generics),+> Kind<($($Generics,)+)> for Brand
| ^^^^^^^^^^^^^^^^^^^^^^ ^^^^^
45 | where
46 | Brand: $KindN<$($Generics),+>,
| ---------------------- unsatisfied trait bound introduced here
...
210 | make_trait_kind!(Kind1, Apply1, "* -> *", (A));
| ---------------------------------------------- in this macro invocation
= note: the full name for the type has been written to '/playground/target/debug/deps/playground-0397c81c81221729.long-type-13968914865257356677.txt'
= note: consider using `--verbose` to print the full type name to the console
= note: this error originates in the macro `make_trait_kind` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting type parameter `F` with trait `Kind1`
|
696 | F: 'a + Kind<(B,)> + Kind<(Apply<Self, (B,)>,)> + Applicative + Kind1<std::sync::Arc<(dyn std::ops::Fn(<VecBrand as Kind<(B,)>>::Output) -> <VecBrand as Kind<(B,)>>::Output + 'a)>>,
| ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to 3 previous errors
But this seems to me to be overly specific to this particular implementation of the trait, so I'm wondering if there's a more general solution I could look into.
I've asked an LLM for some ideas, but I think my particular issue is too advanced and in the weeds for myself so I can't tell if the solutions and ideas it's offering are correct or even relevant. As such, I'd greatly appreciate it if a real human expert can weigh in on the topic and verify (or deny) its suggestions and/or offer alternative solutions/ideas I can look into.