LFLATMAP function applies a macro on each element of a list, producing a list
with the element on top of the stack after each macro invocation.
The macro is called with a stack containing the list index on top and the element at that particular index below it. Since Warp 10 2.4.0, you can override this behaviour with a boolean.
LMAP: if the macro returns a list, then LFLATMAP will produce a
list with the elements of the macro output list (i.e. it will flatten the list).
LMAP FLATTEN: flatten will do the list flattening recursively.