Custom Set

Instructions

Create a custom set type.

Sometimes it is necessary to define a custom data structure of some type, like a set. In this exercise you will define your own set. How it works internally doesn't matter, as long as it behaves like a set of unique elements.

Words

Define a custom-set tuple and declare it an instance of the set mixin with INSTANCE: custom-set set.

• <custom-set> ( -- set ) — construct an empty set.
• >custom-set ( seq -- set ) — build a set from a sequence, silently dropping duplicates.

Then provide M: methods (from sets) on members, in?, adjoin, and set-like for custom-set. With the INSTANCE: declaration and those four methods in place, null?, union, intersect, diff, subset?, set=, and intersects? from the sets vocabulary all work on your set through the protocol's default implementations — the tests call those words directly.

adjoin ( elt set -- ) is mutating: it adds elt to set in place if not already present.