Definição e Invocação

Macro de um parâmetro: double! demonstra substituição textual com literais, aritmética e chamada de função.

// Feature: Macros — basic definition

// Syntax: `macro name(p1, p2) { ... }` + invocation `name!(arg)`

// When to use: generate repetitive code at expansion time (before

// typecheck and lowering). Useful to wrap textual patterns that a

// function cannot capture — `stringify!`, `assert!`, `dbg!`, etc.


// Simplest macro: doubles the received expression.

// Note: parameters are referenced with `$name` in the body.

macro double(x) {
  $x + $x
}


// Invocation uses `!` at the end — convention that distinguishes from a regular function.

let result = double!(21)
print(result)

// expected: 42


// The argument can be any expression — it is pasted textually.

print(double!(5 + 5))

// expected: 20


// Macros are purely syntactic: you can pass identifiers, function

// calls, literals, arithmetic expressions...

fn ten() -> int {
  return 10
}

print(double!(ten()))
// expected: 20

sum3!, show_pair! e pick! mostram múltiplos parâmetros e expansão condicional.

// Feature: Macros with multiple parameters

// Syntax: `macro name(a, b, c) { ... }` — any fixed number of params

// When to use: combine or compare multiple expressions at one expansion

// site.


// Sum of three expressions.

macro sum3(a, b, c) {
  $a + $b + $c
}


print(sum3!(1, 2, 3))

// expected: 6


// Print two arguments with a label.

macro show_pair(label, value) {
  print("{$label} = {$value}")
}


show_pair!("count", 42)
show_pair!("name", "zolo")

// expected:

// count = 42

// name = zolo


// Ternary comparison via macro.

macro pick(cond, a, b) {
  if $cond { $a } else { $b }
}


let x = 7
let max = pick!(x > 5, x, 5)
print(max)
// expected: 7