One other way to add clauses to
qpc's internal database is to
assert them in an embedded command. For example, the sequence:
:- asserta(f(x)). :- f(X), write(X), nl.
in a file given to
qpc will work just as it would if the file
were compiled into the Development System.
There are some problems with asserting clauses like this. One problem is that the asserted clauses will not be available at run-time. If the file had been loaded into the Development System, they would be available when the program was run.
Another problem arises if the compilation of one file depends on facts
that are expected to be asserted into the database during the
compilation of some other file. An approach of this sort may be
useful in the Development System, but it is contradictory to the
notion of independent compilation (see the first figure), which is
one of the important features of
qpc. This problem is not
specific to asserting clauses; it arises with any compile-time
side-effects that are intended to affect future compilation.
It is possible to avoid using separate compilation, by always
recompiling your entire program every time any part of it is modified.
It is still not generally safe to use compile-time side-effects in one
file that affect the compilation of other files. This is because the
order in which files are compiled is different in
qpc finds a command to compile a file, it looks in
that file immediately to find out whether it is a module-file and if
so what are its exports. But it does not actually compile the file
immediately: it puts it on a queue to be compiled when the current
file has been finished with. This is in contrast to compilation in
the Development System, where embedded
compile/1 commands are
processed immediately as they are encountered.
Therefore, it is strongly recommended that side-effects in compile-time code be avoided, or at least restricted so that only the compilation of the current file is affected.