get_char/[1,2] [ISO]get_char(-Char)
get_char(+Stream, -Char)
Unifies Char with the next char from Stream or
with end_of_file if there are no more characters.
Valid input text stream,
defaults to the current input stream.
end_of_file]
Stream errors (see ref-iou-sfh-est), plus:
permission_error