Union

Background

Given a file named “pen.json” with:

{
  "type": "library",
  "dependencies": {}
}

Upcast a number into a union

Given a file named “Foo.pen” with:

f = \() number | none {
  42
}

When I run pen build

Then the exit status should be 0.

Upcast a function into a union

Given a file named “Foo.pen” with:

f = \() (\() number) | none {
  \() number {
    42
  }
}

When I run pen build

Then the exit status should be 0.

Upcast a list into a union

Given a file named “Foo.pen” with:

f = \() [number] | none {
  [number 42]
}

When I run pen build

Then the exit status should be 0.

Downcast a union type

Given a file named “Foo.pen” with:

f = \(x number | none) number {
  if x = x as number {
    x
  } else if none {
    0
  }
}

When I run pen build

Then the exit status should be 0.

Downcast a union type with an else block

Given a file named “Foo.pen” with:

f = \(x number | none) number {
  if x = x as none {
    0
  } else {
    x
  }
}

When I run pen build

Then the exit status should be 0.

Downcast a union type to another union type

Given a file named “Foo.pen” with:

f = \(x number | boolean | none) number | none {
  if x = x as number | none {
    x
  } else {
    none
  }
}

When I run pen build

Then the exit status should be 0.