pyr by example

Type Aliases

type creates a named alias for any type expression. Useful for documenting intent and reducing repetition.

 
type ID = int
type Name = str

struct User {
  id: ID
  name: Name
}

Function types use fn(params) -> return syntax. Aliases make function-typed parameters readable.

 
type Transform = fn(int) -> int

fn apply(x: int, f: Transform) -> int {
  f(x)
}

fn double(x: int) -> int = x * 2
fn negate(x: int) -> int = 0 - x

Inline function types work too, without an alias.

 
fn apply_inline(x: int, f: fn(int) -> int) -> int {
  f(x)
}

Aliases shine when passing multiple functions.

 
fn pipeline(x: int, a: Transform, b: Transform) -> int {
  b(a(x))
}

fn add1(x: int) -> int = x + 1

fn main() {
  println(apply(5, double))
  println(apply(5, negate))

  println(apply_inline(7, fn(x) x * 3))

  println(pipeline(3, add1, double))
}
 
$ pyr run type-aliases.pyr
10
-5
21
8