Type-Safe Abstractions
HKT encoding via GATs lets you write functions generic over Option, Result, Vec, and any container that supports mapping, sequencing, or folding.
Complete Hierarchy
Functor through Monad, Alt through Alternative, Foldable, Traversable, Comonad, and contravariant duals — all with property-based law verification.
Profunctor Optics
Lens, Prism, and composition powered by the profunctor hierarchy. Build reusable, first-class field accessors and pattern matchers.
Ergonomic Macros
do_! flattens nested .and_then() chains. ado_! combines independent computations. Both work with any Monad or Applicative.
Quick Example
Flatten nested error handling with do_!:
use karpal_std::prelude::*;
// Without do_! — rightward drift with every step
fn process(input: &str) -> Option<String> {
parse_id(input).and_then(|id| {
lookup_user(id).and_then(|user| {
check_permissions(&user).and_then(|role| {
Some(format!("{} logged in as {:?}", user.name, role))
})
})
})
}
// With do_! — reads top-to-bottom
fn process(input: &str) -> Option<String> {
do_! { OptionF;
id = parse_id(input);
user = lookup_user(id);
role = check_permissions(&user);
Some(format!("{} logged in as {:?}", user.name, role))
}
}Workspace
| Crate | Description |
|---|---|
karpal-core | HKT encoding, functor hierarchy, Semigroup, Monoid, macros |
karpal-profunctor | Profunctor, Strong, Choice, FnP |
karpal-optics | Profunctor optics: Lens, Prism, composition |
karpal-std | Standard prelude re-exports |
karpal-core and karpal-profunctor are no_std compatible with optional std/alloc feature gates.