Pattern matching

Pattern matching is the primary form of branching in kex. It works in function clauses, match expressions, and destructuring bindings.

`match` expressions

fizzbuzz.kex

let fizzBuzz(n: Int) -> String do
  match (n.modulo(3), n.modulo(5)) do
    (0, 0) -> "FizzBuzz"
    (0, _) -> "Fizz"
    (_, 0) -> "Buzz"
    (_, _) -> "${n}"
  end
end

Multi-clause functions

Define the same function several times against different patterns. Clauses are tried top to bottom.

clauses.kex

let factorial(0) = 1
let factorial(n: Int) = n * factorial(n - 1)

let head([h, *_]) = h
let head([])      = None

Destructuring

destructuring.kex

let (q, r) = divmod(10, 3)

match result do
  Ok(n)    -> "got ${n}"
  Error(e) -> "failed: ${e}"
end

match opt do
  Just(user) -> user.email
  None       -> "no email"
end

`if let`

iflet.kex

if let Just(largest) = shapes.max { |s| s.area }
  IO.printLine("largest area: ${largest}")
end

Guards

A trailing if narrows a clause. The clause only fires if the guard holds.

guards.kex

match n do
  x if x < 0     -> "negative"
  0              -> "zero"
  _              -> "positive"
end