PlAtom versus PlTerm_atom

[mgondan]

At some point, you might wish to explain the difference of the two.

[JanWielemaker]

Af far as I know, PlAtom is a handle to a Prolog atom. That is a constant that can be used during the whole process lifetime. PlTerm_Atom is a way to create a term from an atom. Term handles are volatile. Using explicit atoms is common for extensions as they allow for faster creating of terms as well as comparison that a term holds some atom. Atom handles are sometimes stored in C structures for future reuse.

[mgondan]

Thank you. Peter asked me to open this issue.

Context: I added some PlEncoding arguments to the initializers in a PR for cpp, and I was wondering what PlAtom is being used for.

[JanWielemaker]

Context: I added some PlEncoding arguments to the initializers in a PR for cpp, and I was wondering what PlAtom is being used for.

I think encoding rarely needs to be used with PlAtom as it typically concerns known atoms such as option names or enumerated values for some argumen, i.e., this terms should be the atom a, b or c (in each case doing something) or else raise a domain_error. Still, I'd add PlEncoding for consistency. Eventually, there was the need for PL_new_atom_mbchars(), which is the C implementation to create an atom from a string with given encoding. I think it is used in the JavaScript and Python interfaces.

[mgondan]

PL_new_atom_mbchars()

I have found it already, thanks