# rust2fun (pronounced: rʌstafʌn) [](https://crates.io/crates/rust2fun) [](https://docs.rs/rust2fun/0.2.1/rust2fun/)  A library for functional programming in Rust. ## Build By default, the library is built with the `std` feature enabled. To disable it, use the `--no-default-features` flag. ## Usage Add this to your `Cargo.toml`: ```toml [dependencies] rust2fun = "0.2.1" ``` and import the prelude: ```rust use rust2fun::prelude::*; ``` ## Supported features ### Combinators: - function composition (with [compose](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.compose.html) macro) - pipelines (with [pipe](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.pipe.html) macro) - currying - [curry2](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.curry2.html) macro - [curry3](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.curry3.html) macro - etc - argument flipping (with [flip](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.flip.html) macro) - constant functions - [constant](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.constant.html) macro - [constant1](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.constant1.html) macro (K combinator) - [constant2](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.constant2.html) macro - etc - [id](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.id.html) (I combinator) - [apply](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.apply.html) (A combinator) - [apply_to](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.apply_to.html) (T combinator) - [substitution](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.substitution.html) (S combinator) - [converge](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.converge.html) - [on](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.on.html) (Psi combinator) - [if_else](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.if_else.html) - [fix](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.fix.html) (Y combinator) - no operation - [noop](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.noop.html) - [noop1](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.noop1.html) - [noop2](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.noop2.html) - etc - tuple constructors - [tuple2](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.tuple2.html) - [tuple3](https://docs.rs/rust2fun/0.2.1/rust2fun/combinator/fn.tuple3.html) - etc ### Type classes: - [Semigroup](https://docs.rs/rust2fun/0.2.1/rust2fun/semigroup/trait.Semigroup.html) - [Monoid](https://docs.rs/rust2fun/0.2.1/rust2fun/monoid/trait.Monoid.html) - [Semigroupal](https://docs.rs/rust2fun/0.2.1/rust2fun/semigroupal/trait.Semigroupal.html) - [Invariant](https://docs.rs/rust2fun/0.2.1/rust2fun/invariant/trait.Invariant.html) - [Functor](https://docs.rs/rust2fun/0.2.1/rust2fun/functor/trait.Functor.html) - [Bifunctor](https://docs.rs/rust2fun/0.2.1/rust2fun/bifunctor/trait.Bifunctor.html) - [Pure](https://docs.rs/rust2fun/0.2.1/rust2fun/pure/trait.Pure.html) - [AndThen](https://docs.rs/rust2fun/0.2.1/rust2fun/and_then/trait.AndThen.html) - [Apply](https://docs.rs/rust2fun/0.2.1/rust2fun/apply/trait.Apply.html) - [Applicative](https://docs.rs/rust2fun/0.2.1/rust2fun/applicative/trait.Applicative.html) - [FlatMap](https://docs.rs/rust2fun/0.2.1/rust2fun/flatmap/trait.FlatMap.html) - [Monad](https://docs.rs/rust2fun/0.2.1/rust2fun/monad/trait.Monad.html) + ( [bind!](https://docs.rs/rust2fun/0.2.1/rust2fun/macro.bind.html) notation ) ### Data types: - [NEVec](https://docs.rs/rust2fun/0.2.1/rust2fun/data/ne_vec/struct.NEVec.html) (non-empty vector) - [Validated](https://docs.rs/rust2fun/0.2.1/rust2fun/data/validated/enum.Validated.html) - [ValidatedNev](https://docs.rs/rust2fun/0.2.1/rust2fun/data/validated/type.ValidatedNev.html) ## Examples 1. Function `print_user_credit_card` accepts user(s) wrapped in any effect (Option, Result, Vec, etc.) and prints corresponding credit card(s). ```rust fn get_credit_card(user: User) -> CreditCard { // Get credit card for user } fn print_credit_card(card: CreditCard) { // Print credit card details } fn print_credit_card_of(user: F) where F: Functor, F::Target: Functor<(), Param=CreditCard>, { user.map(get_credit_card).map(print_credit_card); } ``` ...usage: ```rust fn user(id: u32) -> Option { // Get user from database } fn all_users() -> Vec { // Get all users from database } print_credit_card_of(user(1)); print_credit_card_of(all_users()); ``` 2. Validation accumulating all errors. Assuming we have the following validation rules that need to be applied to create a new credit card: ```rust fn validate_number(number: CreditCardNumber) -> Result { // Validating credit card number } fn validate_expiration(date: Date) -> Result { // Validating expiration date } fn validate_cvv(cvv: Code) -> Result { // Validating CVV code } ``` ...we can create a new credit card by applying all validation rules and collecting all errors in a vector `Vec`, non-empty vector `NEVec` (like in the example) or other semigroup (e.g. `String`, `u32`, etc.): ```rust fn validate_credit_card( number: CreditCardNumber, expiration: Date, cvv: Code, ) -> ValidatedNev { ValidatedNev::pure(CreditCard::new) .ap3(validate_number(number).into(), validate_expiration(expiration).into(), validate_cvv(cvv).into()) } ``` ...alternatively, this can be done using the `map3` method: ```rust fn validate_credit_card( number: CreditCardNumber, expiration: Date, cvv: Code, ) -> ValidatedNev { let number: ValidatedNev<_, _> = validate_number(number).into(); let expiration = validate_expiration(expiration).into(); let cvv = validate_cvv(cvv).into(); MapN::map3(number, expiration, cvv, CreditCard::new) } ``` 3. `bind!` notation for monads (like `do` notation in Haskell or `for` comprehension in Scala): Assuming we have the following functions defined: ```rust fn get_opening_prices() -> Vec<(AssetId, i32)> { // Get opening prices from an external service } fn get_closing_prices() -> Vec<(AssetId, i32)> { // Get closing prices from an external service } fn get_asset_name(id: AssetId) -> Option { // Recover asset name for the given id } ``` ...we can use `bind!` notation to calculate daily profit for each asset: ```rust let profits: Vec<(String, i32)> = bind! { for (id_open, opening_price) in get_opening_prices(); for (id_close, closing_price) in get_closing_prices(); let diff = closing_price - opening_price; for name in get_asset_name(id_open).into_iter().collect::>(), if id_open == id_close && diff > 0; (name, diff) }; ``` ## Release notes 0.1.0 (2023-01-22) - Initial release: combinators, Semigroupal, Invariant, Functor, Apply, Applicative, FlatMap, Monad 0.2.0 (2023-09-10) - The project got its logo (thanks [olasinitsyna](https://www.behance.net/olasinitsyna)) - Moved macros imports to the prelude - Added `noopX` and `tupleX` sets of functions - Added type classes: Semigroup, Monoid, Bifunctor + Higher2 (thanks [lrind](https://github.com/lrind)) - Added data types: NEVec, Validated - Added `bind!` notation - Multiple fixes and improvements 0.2.1 (2023-09-21) - Fixed Semigroupal and Apply behavior (thanks [GoldsteinE](https://github.com/GoldsteinE) for the report) - Added type classes: Pure, AndThen - Refactored `mapX` and `apX` functions