pattern_match.nula

// Pattern Matching — exhaustive walk through Nulang's match expressions.
// Covers literal matching, variable binding, wildcards, guards, nested
// patterns, records, and user-declared variant types.
//
// Run with: nulang examples/pattern_match.nula

// User-declared option and result types (there is no prelude — yet!)
type Option[T] = Some(T) | None

// A simple enum for demonstration
type Color = Red | Green | Blue

// -- Literal matching --
fn describe_int(n: Int) -> String {
    match n {
        case 0 => "zero"
        case 1 => "one"
        case n => "other: " + perform Int.to_string(n)
    }
}

// -- Variant matching with payload binding --
fn unwrap_or(opt: Option[Int], default: Int) -> Int {
    match opt with {
        | Some(x) => x
        | None => default
    }
}

// -- Guard expressions --
fn classify(n: Int) -> String {
    match n with {
        | x if x < 0 => "negative"
        | x if x == 0 => "zero"
        | x if x < 10 => "small positive"
        | _ => "large"
    }
}

// -- Nested patterns --
fn describe(opt: Option[Option[Int]]) -> String {
    match opt with {
        | Some(Some(n)) => "nested value: " + perform Int.to_string(n)
        | Some(None) => "outer Some, inner None"
        | None => "outer None"
    }
}

// -- Record field matching --
fn area(rect: { x: Int, y: Int, w: Int, h: Int }) -> Int {
    match rect with {
        | { w: width, h: height } => width * height
    }
}

// -- Variant enum matching --
fn color_code(c: Color) -> Int {
    match c with {
        | Red => 1
        | Green => 2
        | Blue => 3
    }
}

// -- Put it all together --
fn main() {
    perform IO.print(describe_int(0))
    perform IO.print(describe_int(5))
    perform IO.print(perform Int.to_string(unwrap_or(Some(42), 0)))
    perform IO.print(perform Int.to_string(unwrap_or(None, 99)))
    perform IO.print(classify(-5))
    perform IO.print(classify(7))
    perform IO.print(classify(100))
    perform IO.print(describe(Some(Some(7))))
    perform IO.print(describe(Some(None)))
    perform IO.print(describe(None))

    let r = { x: 0, y: 0, w: 10, h: 5 }
    perform IO.print(perform Int.to_string(area(r)))

    perform IO.print(perform Int.to_string(color_code(Blue)))
    0
}