Equivalent of Python pickling in SWI Prolog?

Question

I've got a Prolog program where I'm doing some brute force search on all strings up to a certain length. I'm checking which strings match a certain pattern, keeping adding patterns until hopefully I find a set of patterns that covers all strings. I would like to store which ones to a file which don't match any of my patterns, so that when I add a new pattern, I only need to check the leftovers, instead of doing the entire brute force search again.

If I were writing this in python, I would just pickle the list of strings, and load it from the file. Does anybody know how to do something similar in Prolog?

I have a good amount of Prolog programming experience, but very little with Prolog IO. I could probably write a predicate to read a file and parse it into a term, but I figured there might be a way to do it more easily.

Answer 1

Consider using read/1 to read a Prolog term. For more complex or different kinds of parsing, consider using DCGs and then phrase_from_file/2 with SWI's library(pio).

Answer 2

writeq and read make a similar job, but read the note on writeq about operators, if you declare any.

Answer 3

If you want to write out a term and be able to read it back later at any time barring variables names, use the ISO built-in write_canonical/1 or write_canonical/2. It is quite well supported by current systems. writeq/1 and write/1 work often too, but not always. writeq/1 uses operator syntax (so you need to read it back with the very same operators present) and write/1 does not use quotes. So they work "most of the time" — until they break.

Alternatively, you may use the ISO write-options [quoted(true), ignore_ops(true), numbervars(false)] in write_term/2 or write_term/3. This might be interesting to you if you want to use further options like variable_names/1 to retain also the names of the variables.

Also note that the term written does not include a period at the end. So you have to write a space and a period manually at the end. The space is needed to ensure that an atom consisting of graphic characters does not clobber with the period at the end. Think of writing the atom '---' which must be written as --- . and not as ---. You might write the space only in case of an atom. Or an atom that does not "glue" with .