toExternalString -- convert to a readable string
toExternalString x -- converts x to a string, in such a way
that it can be read back into the program later.
See also toString which simply converts x
to a string which can be displayed meaningfully.
Not everything can be converted to a string in such a way that it
can be read back into the program later, because circular data structures
are common.
Class of returned value: String -- the class of all stringsWays to use toExternalString :