mapcan

(mapcan function list)

Applies function to each element of list -- each call should return a list -- and concatenates the results into a single list. rontolisp joins the pieces with non-destructive append (it does not splice with nconc as standard Common Lisp does). It is a convenient way to map and filter at once: return nil for elements to drop. Single-list form only.

The argument must be a list (nil, the empty list, is accepted); passing a non-list such as a string signals an error rather than silently returning nil. Use map to map over a string or vector.