bea

Chapter 3: Your own types

Bandwagoner

  • records
  • record update
  • label shorthand

A variant with named fields is a record. Coach(name:, former_player:) uses the label shorthand: when a variable has the same name as the field, you write the label once.

Team(team | coach:) copies team with a new coach. It reads like Elixir's map update and compiles to Gleam's Team(..team, coach: coach).

Fields chain with dots: team.coach.name.

Open in playground
pub type Coach {
  Coach(
    name: String,
    former_player: Bool
    )
}

pub type Stats {
  Stats(wins: Int, losses: Int)
}

pub type Team {
  Team(name: String, coach: Coach, stats: Stats)   
}

        

def create_coach(name: String, former_player: Bool) -> Coach {
  Coach(name:, former_player:)
}

def create_stats(wins: Int, losses: Int) -> Stats {
  Stats(wins:, losses:)
}

def create_team(name: String, coach: Coach, stats: Stats) -> Team {
  Team(name:, coach:, stats:)
}

def replace_coach(team: Team, coach: Coach) -> Team {
  Team(team | coach:)
}

def is_same_team(home_team: Team, away_team: Team) -> Bool {
  home_team == away_team
}

def root_for_team(team: Team) -> Bool {
  cond {
    team.coach.name == "Pames Jazo" -> True
    team.coach.former_player -> True
    team.name == "Chicago Bulls" -> True
    _ -> False
  }
}

pub def main() {
  coach1 = create_coach("James Pazo", False)
  coach2 = create_coach("Pames Jazo", False)
  stats = create_stats(21, 12)
  team = create_team("Lapis Panthers", coach1, stats)
  new_team = replace_coach(team, coach2)
  echo new_team

  echo is_same_team(team, new_team)

  echo root_for_team(new_team)
}

An exercism exercise from the Gleam track, solved in Bea: beacode/src/e10_bandwagoner.bea