3.1 KiB
3.1 KiB
effers
effect handlers in rust
how to use
defining effects
effects are defined with traits
trait Printer {
fn print(&mut self, s: &str);
}
trait Logger {
fn debug(&mut self, s: &str);
fn info(&mut self, s: &str);
}
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
#[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
}
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
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)
}
}
running programs
programs are run by providing the corresponding handlers in order, and finally calling the run
method, providing it the required parameters
let result: u8 = Smth.add(IoPrinter).add(FileLogger).run(3);
assert_eq!(result, 6);
full example
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
)
}
}