module string_helpers.

type split_string	int -> string -> string -> string -> o.

doc split_string "
 ``split_string N S FirstN Rest'' succeeds if S has more than N characters
 and the first N are FirstN, and the rest are Rest".

split_string N S FirstN Rest :-
	SLength is (size S),
	SLength > N,
	Prefix iss (substring S 0 N),
	FirstN = Prefix,
	RestOfLength is SLength - N,
	Rest iss substring S N RestOfLength.