SWI-Prolog -- library(charsio)

atom_to_chars/2	Convert Atom into a list of character codes.
atom_to_chars/3	Convert Atom into a difference list of character codes.
format_to_chars/3	Use format/2 to write to a list of character codes.
format_to_chars/4	Use format/2 to write to a difference list of character codes.
number_to_chars/2	Convert Atom into a list of character codes.
number_to_chars/3	Convert Number into a difference list of character codes.
open_chars_stream/2	Open Codes as an input stream.
read_from_chars/2	Read Codes into Term.
read_term_from_chars/3	Read Codes into Term.
with_output_to_chars/2	Run Goal as with once/1.
with_output_to_chars/3	Run Goal as with once/1.
with_output_to_chars/4	Same as with_output_to_chars/3 using an explicit stream.
write_to_chars/2	Write a term to a code list.
write_to_chars/3	Write a term to a code list.