function
boot.janet on line 2065 , column 1
(flatten-into into ind )
Appends the depth-first traversal of an indexed type `ind` into a
given array `into` . Returns `into` .
(flatten-into @[1 2 3 ] @[[4 5 6 ] @[7 8 9 ] @[10 11 12 ]]) # => @[1 2 3 4 5 6 7 8 9 10 11 12]