What is "compile time"?

[jjtolton]

prolog_load_context(module, Module) :-
    %% The source module (see ref-mod-mne). This is useful for example
    %% if you are defining clauses for user:term_expansion/6 and need
    %% to access the source module at compile time.
    '$prolog_lc_module'(Module).

🤔

Does this mean rust compile time or is there a Prolog execution compilation phase? 🤔

[triska]

This does not mean Rust compile time, since this is—and refers to—Prolog code and thus presumes a working Prolog engine.

Scryer Prolog compiles Prolog code to Warren Abstract Machine (WAM) instructions, and in the future will compile such instructions to native code (#2424). When preparing Prolog text for execution, Scryer Prolog gives us a chance to automatically rewrite code in this phase, i.e., during compilation time (of Prolog code), by means of defining the predicates goal_expansion/2 and term_expansion/2 that relate Prolog terms that occur in the program to target terms that are compiled instead. See for instance library(dcgs) for usage examples of these facilities:

scryer-prolog/src/lib/dcgs.pl

Line 258 in 2f47343

user:goal_expansion(phrase(GRBody, S, S0), GRBody2) :-

Quoting the Prolog ISO standard:

7.5.1 Preparing a Prolog text for execution

Preparing a Prolog text for execution shall result in the
complete database and processor being in an initial state
of execution.

The means by which a Prolog processor is asked to prepare
standard-conforming Prolog texts (6.2) for execution shall
be implementation defined. The manner in which a Prolog
processor prepares standard-conforming Prolog texts for
execution shall be implementation dependent. This process
converts the read-terms in a Prolog text to the clauses of
user-defined procedures in the database.

All clauses of a procedure are ordered for execution
according to the textual (or temporal) order of these
clauses as they were prepared for execution.

Any effects of reordering, adding or removing clauses by
directives during preparation for execution are implemen-
tation defined.

The clauses of different procedures have no temporal or
spatial correlation.

The effect of directives while preparing a Prolog text for
execution is defined in (7.4.2).

[UWN]

In many situations in the context of Prolog, compile time is the time when a term is converted to a clause and in particular to the body of a clause (7.6.2). This can be observed by the errors produced or not produced.

?- call((fail,1)).
   error(type_error(callable,(fail,1)),(',')/2). % conversion failed
?- call((fail,call(1))).
   false. % no conversion