-- Literal-int dot-index for lists: `xs.0` is sugar for `at xs 0`.
-- Use it when the index is a literal number known at parse time.
-- For a variable index, write `at xs i` instead.
frst xs:L n>n;xs.0
thrd xs:L n>n;xs.2
nest>n;xss=[[1,2],[3,4]];xss.0.1
-- run: frst [10,20,30]
-- out: 10
-- run: thrd [10,20,30]
-- out: 30
-- run: nest
-- out: 2