07_effects.nula

// 07_effects.nula - Algebraic effects
// Demonstrates: perform, handle, effect composition, IO effects,
//               string and int conversion effects
//
// Run: nulang examples/07_effects.nula

// Basic effect handling: intercept a performed effect and return a value
let answer = handle perform Math.getAnswer() with {
    | Math.getAnswer() => 42
}
perform IO.print("The answer is " + perform Int.to_string(answer))

// Handler with computed value
let computed = handle perform Math.getAnswer() with {
    | Math.getAnswer() => 6 * 7
}
perform IO.print("Computed answer: " + perform Int.to_string(computed))

// Effect that returns a string
let greeting = handle perform Math.getGreeting() with {
    | Math.getGreeting() => "Hello from effects!"
}
perform IO.print(greeting)

// Multiple performs in a block, single handler
let result = handle {
    let a = perform Math.getAnswer()
    let b = perform Math.getAnswer()
    a + b
} with {
    | Math.getAnswer() => 10
}
perform IO.print("Double answer: " + perform Int.to_string(result))

// Built-in effects: IO.print works without explicit handler
perform IO.print("IO.print is a built-in effect!")

// String effects
let len = perform String.length("Nulang")
perform IO.print("Length of Nulang: " + perform Int.to_string(len))

let ch = perform String.charAt("Nulang", 0)
perform IO.print("First char code: " + perform Int.to_string(ch))

// Int.to_string: convert int to string
let s = perform Int.to_string(2024)
perform IO.print("The year is " + s)