Structs are named-indexed collections of references to values.

Structs have two parts: a type which declares the field names and an optional parent struct type; and an instance of a struct type which has a reference to a value for each field.

;; define a struct foo with fields a and b -- the define-struct form
;; does not define a parent type
define-struct foo a b

;; create an instance of a foo with values 3 and 6
foo1 := make-foo 3 6

;; a function to check the fields
define (checker si) {
  if (not (foo? si)) {
    printf "a %s is not a foo: %s\n" (type->string si) si
  } {
    if ((struct-instance-ref si 'b) gt (struct-instance-ref si 'a)) {
      printf "b > a for %s\n" si
    } {
      printf "b <= a for %s\n" si

checker "bob"

checker foo1

;; meddle with foo1
foo1.b = 1
checker foo1
$ idio simple-structs
a string is not a foo: bob
b > a for #<SI foo a:3 b:6>
b <= a for #<SI foo a:3 b:1>

Last built at 2023-11-09T07:11:45Z+0000 from 77077af (dev) for Idio 0.3