boot.janet on line 1472, column 1
(match x & cases)
Pattern matching. Match an expression x against any number of cases.
Each case is a pattern to match against, followed by an expression to
evaluate to if that case is matched. A pattern that is a symbol will
match anything, binding x's value to that symbol. An array will match
only if all of it's elements match the corresponding elements in x. A
table or struct will match if all values match with the corresponding
values in x. A tuple pattern will match if it's first element matches,
and the following elements are treated as predicates and are true. The
last special case is the '_ symbol, which is a wildcard that will match
any value without creating a binding. Any other value pattern will only
match if it is equal to x.