Question

I am having the hardest time figuring this out, even though it is one of the simplest things to do in other languages: Is there a simple way to read the entire contents of a text file into a Prolog variable?

Answer 1

Simply state with a DCG what you want to describe, and use library(pio) to parse from a file:

:- use_module(library(pio)).

all([])     --> [].
all([L|Ls]) --> [L], all(Ls).

Example:

?- once(phrase_from_file(all(Ls), 'all.pl')).
Ls = [10, 58, 45, 32, 117, 115, 101, 95, 109|...].