TIL: No `if`s in Gleam

Sep 17, 2025· Yan Yi Goh· 2 min read

Gleam does not have an if statement. The Exercism exercise required me to return a custom type based on whether it’s True or False.

pub fn get_treasure(
  chest: TreasureChest(treasure),
  password: String,
) -> UnlockResult(treasure) {
  case chest.password == password {
    True -> Unlocked(chest.value)
    False -> WrongPassword
  }
}

Now, trying alternatives, I came up with the following with bool.guard to get things to still work:

pub fn get_treasure(
  chest: TreasureChest(treasure),
  password: String,
) -> UnlockResult(treasure) {
  { chest.password == password }
  |> bool.guard(return: Unlocked(chest.value), otherwise: fn() { WrongPassword } )
}

Not as readable, in my opinion. Or, following the gleam/bool documentation with use, I could do the following like how I early-return in Go:

pub fn get_treasure(
  chest: TreasureChest(treasure),
  password: String,
) -> UnlockResult(treasure) {
  use <- bool.guard(when: chest.password == password, return: Unlocked(chest.value))
  WrongPassword
}

The syntax looks wonky 😵‍💫 (just like me being a noob reading Rust code). Need to write more Gleam. Here’s a Go comparison where the language often promotes early-returns:

// Go does not have sum type, so I am just giving an arbitary example for early returns.
func getTreasure(chest: TreasureChest, password: string) UnlockResult {
  if chest.password == password {
    return Unlocked{ value: chest.value }
  }

  return WrongPassword
}