Practical use of improper lists in Erlang (perhaps all functional languages)

Question

I\'ve been reading Erlang and OTP in action, and stumbled upon a question with regards to improper lists.

Don’t be tempted to use list cel

Answer 1

OTP standard digraph module for directed graphs uses improper lists for tagged vertex and edge identifiers. For example, vertex 42 would be identified as ['$v'|42], which means a pair of an atom (no, not a character literal!) and an integer, similarly edge 97 would be ['$e'|97].