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Singleton

Purpose

Sometimes, when we are creating libraries for other users, we might want to group similar functions together to improve user experience.

Example

Suppose we are creating a library that allow the user to access the file system. And we wish that our code looks like this:
=fs.open("Hello world.txt")
First, we need to create a tagged union with only a single tag:
FileSystem = choice.new
Then, create a constant alias:
fs = FileSystem.new
After that, we can proceed to define the functions we intend to expose:
(this FileSystem).open(filename String) = undefined
(this FileSystem).rename(oldname String) as(newname String) = undefined
(this FileSystem).delete(filename String) = undefined
And the client can use them as follows:
=fs.open("Hello world.txt")
=fs.rename("Jojo.md") as("Koko.md")
=fs.delete("/")