Empty list and single item list

[qhwa]

Problem

Empty list and one-element list are currently not possible.

Proposal

[]
[foo]

For multi-elements list, we can use:

[foo, bar]

Question: shall we deprecate implied list? (a,b,c)
Nope, they are useful when specifying input stubs.

Question: shall we support nested list? ([a, [b, c]])
Nope, for inputs, there are no such use cases. For output, using function code would be easier. But we may review it in the future.