karpal-free 0.4.0

Free constructions (Coyoneda, Yoneda) for the Industrial Algebra ecosystem
Documentation

karpal-free

Free constructions for the Industrial Algebra ecosystem.

What's included

Type Description
Coyoneda<F, A> Free functor — makes any type constructor into a Functor by deferring fmap
Yoneda<F, A> Yoneda lemma as a data type — O(1) map fusion via CPS
Free<F, A> Free monad — Pure(A) | Roll(F<Free<F, A>>)
Cofree<F, A> Free comonad — annotated recursive structure with head + tail
Freer<F, A> Freer monad — no F: Functor requirement (uses Coyoneda internally)
Lan<G, H, A, B> Left Kan extension
Ran Right Kan extension (trait-based)
Codensity<F, A> CPS monad — no F bounds for pure/fmap/chain
Density<W, A> CPS comonad — no W bounds for extract/fmap
Day<F, G, A, B, C> Day convolution — combines two functors via a binary function
FreeAp<F, A> Free applicative — supports static analysis via count_effects
FreeAlt<F, A> Free alternative — Vec<FreeAp<F, A>>

Usage

use karpal_free::{Coyoneda, Yoneda, Free, Cofree};
use karpal_core::hkt::OptionF;

// Coyoneda: fmap without Functor
let co = Coyoneda::<OptionF, i32>::lift(Some(1))
    .fmap(|x| x + 1)
    .fmap(|x| x * 10);
assert_eq!(co.lower(), Some(20));

// Yoneda: O(1) map fusion
let yo = Yoneda::<OptionF, i32>::lift(Some(1))
    .fmap(|x| x + 1)
    .fmap(|x| x * 10);
assert_eq!(yo.lower(), Some(20));

Free monad

use karpal_free::Free;
use karpal_core::hkt::OptionF;

// Pure values
let pure: Free<OptionF, i32> = Free::pure(42);

// Roll wraps one layer of the functor
let rolled: Free<OptionF, i32> = Free::roll(Some(Free::pure(42)));

Features

  • std (default) — enables alloc and standard library support
  • alloc — enables heap-allocated types (Box<dyn Fn>)
  • With default-features = false, the crate is no_std compatible (but most types require alloc)

License

MIT OR Apache-2.0