There are two library files for reading sentences. One of them is
library(readin), which defines the single predicate read_in/1.
library(readin) was written to be used.
library(readsent) was originally written to be read and
modified, as
everyone has a different idea of how sentence reading should be done.
Nevertheless, you may find read_sent/1 to be quite useful.
Both sentence readers work by reading characters until some termination
condition and then parsing a list of character codes using a Definite
Clause Grammar. You can have any number of grammars in one Prolog
program. You will probably find that read_in/1 does most of what you
want, but if you want to do something different you may find it easier
to modify read_sent/1.