(string-read-line! string) -> string, or #f
This will read from the beginning of the string until it reaches either "\n" or "\r\n". If neither of these is found in the string, #f will be returned. This should not be taken to mean that the string is empty, merely that no further line-separators may be found within it.
Example:
>> (define a a "Testing!\nTesting 1 2 3!\r\nCan anybody hear me?") :: "Testing! Testing 1 2 3! Can anybody hear me?" >> (string-read-line! a) :: "Testing!" >> (string-read-line! a) :: "Testing 1 2 3!" >> (string-read-line! a) :: #f