04_pattern_match.nula

// 04_pattern_match.nula - Pattern matching
// Demonstrates: match on literals, variables, wildcards, guards,
//               variants, tuples, and record patterns
//
// Run: nulang examples/04_pattern_match.nula

// Custom option type
type Option[T] = Some(T) | None
type Color = Red | Green | Blue

// Literal matching
let describe_int = fn(n) {
    match n with {
        | 0 => "zero"
        | 1 => "one"
        | 2 => "two"
        | n => "other: " + perform Int.to_string(n)
    }
}
perform IO.print(describe_int(0))
perform IO.print(describe_int(2))
perform IO.print(describe_int(42))

// Variant matching with payload binding
let unwrap_or = fn(opt, default) {
    match opt with {
        | Some(x) => x
        | None => default
    }
}
perform IO.print(perform Int.to_string(unwrap_or(Some(42), 0)))
perform IO.print(perform Int.to_string(unwrap_or(None, 99)))

// Guards
let classify = fn(n) {
    match n with {
        | x if x < 0 => "negative"
        | x if x == 0 => "zero"
        | x if x < 10 => "small"
        | _ => "large"
    }
}
perform IO.print(classify(-5))
perform IO.print(classify(0))
perform IO.print(classify(7))
perform IO.print(classify(100))

// Tuple matching
let sum_tuple = fn(t) {
    match t with {
        | (x, y) => x + y
    }
}
perform IO.print("sum(1,2) = " + perform Int.to_string(sum_tuple((1, 2))))
perform IO.print("sum(10,20) = " + perform Int.to_string(sum_tuple((10, 20))))

// Record pattern matching
let area = fn(rect) {
    match rect with {
        | { w: width, h: height } => width * height
    }
}
let r = { x: 0, y: 0, w: 10, h: 5 }
perform IO.print("area = " + perform Int.to_string(area(r)))

// Enum matching
let color_code = fn(c) {
    match c with {
        | Red => 1
        | Green => 2
        | Blue => 3
    }
}
perform IO.print("Red = " + perform Int.to_string(color_code(Red)))
perform IO.print("Blue = " + perform Int.to_string(color_code(Blue)))

// Alias patterns
let inspect = fn(opt) {
    match opt with {
        | s @ Some(x) => "Some(" + perform Int.to_string(x) + ")"
        | None => "None"
    }
}
perform IO.print(inspect(Some(7)))
perform IO.print(inspect(None))