It always amazes me when I try out a new programming language and find that the standard library doesn't include join and split functions. join is used to combine a list of strings into a single string with each item separated by a delimiter. split takes a delimited string and divides it into sub-strings. Python, thankfully, does provide these functions:

>>> ':'.join(['a','b','c'])
'a:b:c'
>>> 'a:b:c'.split(':')
['a', 'b', 'c']

Erlang provides regexp:split but it looks like I have to add my own join function. Not sure this is the most efficient implementation but it will do the job:

intersperse(_, []) -> [];
intersperse(Element, List) ->
tl(lists:reverse(lists:foldl(fun(X, A) -> [X,Element|A] end, [], List))).

join(List, ListOfLists) -> lists:append(intersperse(List, ListOfLists)).

> intersperse(":", ["a","b","c"]).
["a",":","b",":","c"]
> join(":", ["a","b","c"]).
"a:b:c"

And since strings in Erlang are just lists of integers this can be applied to other lists as well.