Frust

Functional programming in Rust. Still largely a WIP.

General idea

Hopefully, make things easier by allowing stuff like this:

use frust::monoid::*;

let v = vec![Some(1), Some(3)];
assert_eq!(combine_all(&v), Some(4));

// Slightly more magical
let t1 =       (1, 2.5f32,                String::from("hi"),  Some(3));
let t2 =       (1, 2.5f32,            String::from(" world"),     None);
let t3 =       (1, 2.5f32,         String::from(", goodbye"), Some(10));
let tuples = vec![t1, t2, t3];

let expected = (3, 7.5f32, String::from("hi world, goodbye"), Some(13));
assert_eq!(combine_all(&tuples), expected);

Examples

Semigroup

Things that can be combined.

use frust::semigroup::*;

assert_eq!(Some(1).combine(&Some(2)), Some(3));

assert_eq!(All(3).combine(&All(5)), All(1)); // bit-wise && 
assert_eq!(All(true).combine(&All(false)), All(false));

let vec_of_some_strings = vec![Some(String::from("Hello")), Some(String::from(" World"))];
assert_eq!(combine_all(&vec_of_some_strings), Some(String::from("Hello World")));

Monoid

Things that can be combined and have an empty/id value.

use frust::monoid::*;

let t1 = (1, 2.5f32, String::from("hi"), Some(3));
let t2 = (1, 2.5f32, String::from(" world"), None);
let t3 = (1, 2.5f32, String::from(", goodbye"), Some(10));
let tuples = vec![t1, t2, t3];

let expected = (3, 7.5f32, String::from("hi world, goodbye"), Some(13));
assert_eq!(combine_all(&tuples), expected)

let product_nums = vec![Product(2), Product(3), Product(4)];
assert_eq!(combine_all(&product_nums), Product(24))

HList

Statically typed heterogeneous lists. Pop as much as you want from one of these; everything remains typed.

#[macro_use] extern crate frust;
use frust::hlist::*;

let h = hlist![true, "hello", Some(41)];
let (h1, tail1) = h.pop();
assert_eq!(h1, true);
assert_eq!(tail1, hlist!["hello", Some(41)]);

Todo

It makes sense to start by implementing things that are useful even for idiomatic Rust usage (efficient, and safe). The following might be nice to have:

1. Validation (See cats)

These are not implemented at all, nor do I know for sure if they are possible given that Rust has no support for Higher Kinded Types. In addition, Rustaceans are used to calling iter() on collections to get a lazy view, manipulating their lists, and then doing a collect() at the end to keep things efficient. The use of these following structures maybe limited in that context.

0. Functor
1. Monad
2. Apply
3. Applicative

Show, Monoid, HList, and Semigroup are at least partially (mostly?) implemented.

Benchmarks would be nice but they're an unstable feature, so perhaps in a different branch.

Inspirations

Scalaz, Cats, Haskell, the usual suspects ;)

Contributing

Yes please !

The following are considered important, in keeping with the spirit of Rust and functional programming:

• Safety (type and memory)
• Efficiency
• Correctness