Multiple Return Values

Any Dylan expression may return multiple values and those values can be captured by let. Using round as an example:

let (integer, remainder) = round(3.2);

Here integer is bound to the value 3 and remainder is bound to the value 0.2.

Any function may return multiple values by calling the values function in return position:

define function parse-integer
    (input :: <string>) => (integer :: <integer>, end-pos :: <integer>)
  let integer = 0;
  let pos = 0;
  ...code that sets pos and integer...
  values(integer, pos)

Call it like this:

let (int, epos) = parse-integer("123 blah");

or like this if you don’t need the second value:

let int = parse-integer("123 blah");

Sometimes you may have a <sequence> of known values and want to bind them to variables temporarily:

let point = #(100, 200, 300);
let (x, y, z) = apply(values, point);

You may bind multiple trailing values to a single variable by using #rest. In the following example more will be bound to #(3, 4, 5).

let (first, second, #rest more) = values(1, 2, 3, 4, 5);

Extra values are ignored and missing values are bound to #f:

let (x, y) = values(1, 2, 3);
// x = 1, y = 2

let (x, y, z) = values(1, 2);
// x = 1, y = 2, z = #f