List comprehensions

[darrylabbate]

There are any number of ways to design a list comprehension syntax, so not really concerned with those details at the moment. Though I'd want it to be delimited by braces ([]) like many other languages.

The only tricky constraint is to be able to support list comprehensions as well as vanilla "list" literals in the form [0,1,2,...]. Python, as an example, doesn't allow the two syntaxes to coincide in the same literal. That's a reasonable restriction, though it doesn't really help wrt the compiler disambiguating a list comprehension from a vanilla literal. The biggest thing would be a syntax where the "output expression" is the first element (most common style). If the syntax had some other unique token first, it'd be a non-issue.

Ref:

• https://en.wikipedia.org/wiki/List_comprehension
• https://en.wikipedia.org/wiki/Comparison_of_programming_languages_(list_comprehension)
• https://rosettacode.org/wiki/List_comprehensions