* effers
effect handlers in rust

** how to use
*** defining effects
effects are defined with traits

#+begin_src rust
trait Printer {
    fn print(&mut self, s: &str);
}
trait Logger {
    fn debug(&mut self, s: &str);
    fn info(&mut self, s: &str);
}
#+end_src

all the trait functions (that are used in programs) must take ~&mut self~ as a parameter

*** defining a program

programs are defined as a normal function, with the added ~program~ attribute

#+begin_src rust
#[program(Smth => Printer(print as p), Logger(debug, info))]
fn smth(val: u8) -> u8 {
    p("hey hi hello");

    debug("this is a debug-level log");
    info("this is a info-level log");

    val + 3
}
#+end_src

the first token (~Smth~) will be the name of the program. effects are listed after the ~=>~ token

**** listing effects
effects are listed by writing the trait's name, followed by a parenthesized list of the functions that will be used

functions can be given an alias using the ~as~ keyword

*** defining effect handlers
effect handlers are defined by declaring a struct, and implementing the trait on it

#+begin_src rust
struct IoPrinter;
impl Printer for IoPrinter {
    fn print(&mut self, s: &str) {
        println!("{}", s)
    }
}

struct FileLogger;
impl Logger for FileLogger {
    fn debug(&mut self, s: &str) {
        println!("debug: {}", s)
    }
    fn info(&mut self, s: &str) {
        println!("info: {}", s)
    }
}
#+end_src

*** running programs
programs are run by providing the corresponding handlers in order, and finally calling the ~run~ method, providing it the required parameters

#+begin_src rust
let result: u8 = Smth.add(IoPrinter).add(FileLogger).run(3);
assert_eq!(result, 6);
#+end_src

** full example
#+begin_src rust
use effers::program;

#[program(Smth => Printer(print as p), Logger(debug, info))]
fn smth(val: u8) -> u8 {
    p("hey hi hello");

    debug("this is a debug-level log");
    info("this is a info-level log");

    val + 3
}

fn main() {
    // maybe smth like this?
    let result: u8 = Smth.add(IoPrinter).add(FileLogger).run(3);
    assert_eq!(result, 6);
    let other_result: u8 = Smth
        .add(IoPrinter)
        .add(NetworkLogger {
            credentials: "secret password".to_string(),
        })
        .run(8);
    assert_eq!(other_result, 11);
}

// effects
trait Printer {
    fn print(&mut self, s: &str);
}
trait Logger {
    fn debug(&mut self, s: &str);
    fn info(&mut self, s: &str);
}

struct IoPrinter;
impl Printer for IoPrinter {
    fn print(&mut self, s: &str) {
        println!("{}", s)
    }
}

struct FileLogger;
impl Logger for FileLogger {
    fn debug(&mut self, s: &str) {
        println!("debug: {}", s)
    }
    fn info(&mut self, s: &str) {
        println!("info: {}", s)
    }
}

struct NetworkLogger {
    credentials: String,
}
impl Logger for NetworkLogger {
    fn debug(&mut self, s: &str) {
        println!(
            "debug through network: {}; with password {}",
            s, self.credentials
        )
    }
    fn info(&mut self, s: &str) {
        println!(
            "info through network: {}; with password {}",
            s, self.credentials
        )
    }
}
#+end_src