Defs

A Def names a computation. Reading it computes a Bag from data, without changing any data.

Name a computation

def declares a Def. Other Defs can use its name:

def colors = {"red", "blue", "blue"}
def color_names = colors%

color_names // {"blue", "red"}

Name steps with let

Inside braces, let names an intermediate result. The name is available after its let, and it cannot change:

def built = {
  let first! f64 = 1
  let second! f64 = first + 1
  {first, second}
}

built // {1, 2}

The braces collect their expressions into one result Bag. A let names a result without adding it to that Bag.

A binder can name the parts of a result: let [x, y] = point selects its Tuple positions, and let (name: label) = item selects a Record field. Add a whole name with @ to keep both:

def described_point = {
  let point @ [x, y] = [3, 4]
  (point: point, squared: x * x + y * y)
}

described_point // {(point: [3, 4], squared: 25)}

The same binder works in a kernel header: rows map row @ (name: label) => [row, label] names each whole row and its name field.

SakaQL works out each Def’s Set and cardinality from its expression. You can also state a contract, and the result must fit it.