functype-io

Lazy, composable IO effect type for Rust.

Part of the functype library.

IO<A>

A deferred computation that produces a value of type A or fails with an error. Nothing executes until .run() is called.

use functype_io::IO;

let io = IO::effect(|| {
    println!("side effect!");
    42
}).map(|x| x * 2);

// Nothing printed yet
let result = io.run().unwrap(); // prints "side effect!", returns 84

Features

• Constructors — succeed, fail, effect, effect_result, from_result, from_option, from_either
• Combinators — map, flat_map, zip, zip_with, then, tap
• Error handling — map_error, catch, or_else, either(), retry
• Resource safety — bracket (acquire/use/release), ensuring (finalizer)
• Async interop — from_future, to_future
• Do-notation — Works with fdo! macro via and_then/map

Usage

[dependencies]
functype-io = "0.1"

use functype_io::IO;
use functype_core::fdo;

let result = fdo! {
    x <- IO::succeed(10);
    y <- IO::succeed(20);
    yield x + y
};
assert_eq!(result.run().unwrap(), 30);

License

MIT OR Apache-2.0