Pattern Matching

Haira's match expression supports powerful pattern matching.

Basic Match

match status {
    "active" => io.println("Active"),
    "inactive" => io.println("Inactive"),
    _ => io.println("Unknown")
}

Or-Patterns

Match multiple values with |:

match day {
    "Saturday" | "Sunday" => io.println("Weekend"),
    _ => io.println("Weekday")
}

Range Patterns

Match numeric ranges:

match score {
    90..=100 => "A",
    80..90 => "B",
    70..80 => "C",
    60..70 => "D",
    _ => "F"
}

.. is exclusive end, ..= is inclusive.

Guards

Add conditions to match arms:

match value {
    n if n > 0 => io.println("Positive"),
    n if n < 0 => io.println("Negative"),
    _ => io.println("Zero")
}

Enum Matching

enum Shape {
    Circle(float)
    Rectangle(float, float)
    Point
}

match shape {
    Shape.Circle(r) => 3.14 * r * r,
    Shape.Rectangle(w, h) => w * h,
    Shape.Point => 0.0
}

The compiler warns if your match is not exhaustive over an enum type.

Combining Patterns

match response_code {
    200 | 201 => "Success",
    301 | 302 => "Redirect",
    400 => "Bad Request",
    401 | 403 => "Unauthorized",
    404 => "Not Found",
    code if code >= 500 => "Server Error",
    _ => "Unknown"
}

Match with Blocks

match command {
    "deploy" => {
        build()
        test()
        deploy()
        io.println("Deployed!")
    },
    "test" => {
        test()
        io.println("Tests passed!")
    },
    _ => io.println("Unknown command: ${command}")
}

Codegen

The compiler generates a Go switch for simple matches and an if/else if chain when guards or range patterns are present.