parallel

parallel expressions allow you to do things in parallel, and then do things with their results.

A parallel expression is built up from multiple parts:

• expressions or statements that return a Promise or a Result
• an optional then branch
• catch branches
• an optional finally branch

An example:

parallel {
  articles =
    loadImages()

  users =
    loadUsers()
} then {
  next {
    articles = articles,
    users = users,
  }
} catch {
 /* errors are caught here. */
} finally {
  /* Clean things up here. */
}

Keep in mind that you need to handle all possible errors that can be returned from a statement, although the compiler has your back here and will show an error if you forget one.

The return value of a parallel expression is always a Promise(error, result) :

• If the value of the then branch is a Promise then it will be returned as is
• If the value of the then branch is not a Promise then it will return a promise which never fails Promise(Never, result) where the result is the value of the then branch
• If there is no then branch then the return value is Promise(Never, Void)

A few notable things to keep in mind:

• All of the catches must match the return value of the last statement
• Results are unwrapped into variables
• Promises are await -ed and unwrapped into variables