Skip/pass non-standard prolog code - prolog

Question

I'm developing under SWI-Prolog, but my target is Erlog (https://github.com/rvirding/erlog). I need a way to use non-standard Prolog syntax.
Is there a way to write prolog code that will be disregarded by the SWI-compiler i.e. make it invisible.
Here is example how does it look like :
do_stuff(G,Amt) :- ecall(erlog_demo:efunc('Elixir.Blah':stuff({G,Amt})).
I was thinking if there is a way for SWI to skip that and I have another declaration that does nothing.
do_stuff(_,_).
One option probably is to comment it and then use parser to remove the comment before running in Erlog, but this seem cumbersome.
Any other ideas.
======
is_dialect(swi) :- catch(current_prolog_flag(dialect, swi), _, fail).
:- if(is_dialect(swi)).
do_stuff(_,_).
:- else.
do_stuff(G,Amt) :- ecall(erlog_demo:efunc('Elixir.Blah':stuff({G,Amt})).
:- endif.
Syntax error: Operator expected

Answer 1

I use this idiom to keep code running in different implementations
:- if(swi).
gen_hash_lin_probe(Key, HashTable, Value) :-
arg(_, HashTable, E),
nonvar(E),
E = Key-Value.
:- elif(yap).
gen_hash_lin_probe(Key, HashTable, Value) :-
HashTable =.. [htlp|Args],
nth1(_, Args, E),
nonvar(E),
E = Key-Value.
:- endif.
where predicates swi/0 or yap/0 are imported from this module(prolog_impl)
:- module(prolog_impl, [swi/0, yap/0, prolog_impl/1]).
swi :- prolog_impl(swi).
yap :- prolog_impl(yap).
prolog_impl(K) :-
F =.. [K,_,_,_,_],
current_prolog_flag(version_data, F).

Answer 2

One closing parenthesis is missing in the "else" branch.
do_stuff(G,Amt) :- ecall(erlog_demo:efunc('Elixir.Blah':stuff({G,Amt})). % BAD
do_stuff(G,Amt) :- ecall(erlog_demo:efunc('Elixir.Blah':stuff({G,Amt}))). % OK!
Simply count the number of opening parentheses. When . (period, full-step) is reached the difference count of opening vs closing must amount to exactly zero.
Hope that helps!

Answer 3

This answer is based, in part, on
#Capelli's answer and your comments on his candidate solution.
We propose a different way. Follow the dots step-by-step...
For a start, we take the following simplified and shortened snippet.
:- if(true). p(3).
:- elif(false). p(4+3).
:- endif.
In above sample we can see that the "else" branch is never taken, ever.
So... could we, in principle, put arbitrary text and binary data there?
:- if(true). p(3).
:- elif(false). p (4);;[ p())
:- endif.
нет! Upon (re-)loading, we get: ⚠ Syntax error: Operator expected
TIL that all sections between elif and endif must be valid Prolog text.
Let's try something different which was inspired by that phrases you used, in particular: "[...] use non-standard Prolog syntax [...] code that will be disregarded [...] make it invisible [...]"
To me, the phrase "non-standard syntax" indicates that new operator(s) might be introduced (or old ones redefined):
:- op(500,xfx,=>).
:- if(true). p(2).
:- elif(false). p(3 => 3).
:- endif.
Consider the following variation:
:- if(true). p(2).
:- elif(false). :- op(500,xfx,=>). % is moving the `op/3` here ok?
p(3 => 3).
:- endif.
нет! Upon (re-)loading, we get: ⚠ Unterminated conditional compilation from [...]
There is another way! We can proceed by inserting a special-purpose end_of_file fact to tell the Prolog text reader to disregard everything after end_of_file.
We use it like this:
% snip_at_end.pl
xxx1.
xxx2.
end_of_file.
xxx3.
:- op (500, xfx,eat). % broken syntax (pt.1)
1 ]][[ v % broken syntax (pt.2)
Simple test using SICStus Prolog:
$ sicstus
SICStus 4.3.2 (x86_64-linux-glibc2.12): Fri May 8 01:05:09 PDT 2015
[... License information ...]
| ?- compile(snip_at_end).
% compiling /home/stefan/prolog/snip_at_end.pl...
% compiled /home/stefan/prolog/snip_at_end.pl in module user, 40 msec 400672 bytes
yes
| ?- xxx1.
yes
| ?- xxx2.
yes
| ?- xxx3.
! Existence error in user:xxx3/0
! procedure user:xxx3/0 does not exist
! goal: user:xxx3
Hope this helps! I'm curious / interested if my answer fits your problem:)