# :-multifile and DCG rules being stubborn, predicate fails immediately **URL:** \ **Category:** General\ **Created:** [April 5, 2021, 1:50pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796 "2021-04-05T13:50:49Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 1:50pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/1 "2021-04-05T13:50:49Z")
I decided to split my growing DCG rules (ast.pl) across one file per handler, I added the module search path but things are not working and I also have the error: ```prolog | Warning: /Users/sean/Documents/code/prolog/the-f-word-project/src/ast/ast.pl:37: Warning: Local definition of ast:inst/4 overrides weak import from defun ``` I understand what causes this message but right now I am not sure what to do about it and feeling a little confused about just how to break out my big sprawling ast file into smaller more manageable files. Ideally I want a single file for each syntax form, so one for defun, defvar, emit, blah blah. I currently have the following folder structure from the project root ``` src/ ast/ ast.pl inst/ defun.pl, .plt defvar.pl, .plt tokeniser coder ``` I have this code in my `load.pl` which sets up the module paths (IIUIC) so that I can then import my modules and they get found: ```prolog :- multifile user:file_search_path/2. :- prolog_load_context(directory, Dir), asserta(user:file_search_path(myapp, Dir)), format(atom(Src), '~s/src', [Dir]), asserta(user:file_search_path(myapp, Src)), format(atom(Ast), '~s/src/ast', [Dir]), asserta(user:file_search_path(myapp, Ast)), format(atom(Inst), '~s/src/ast/inst', [Dir]), asserta(user:file_search_path(myapp, Inst)), format(atom(Tok), '~s/src/tokeniser', [Dir]), asserta(user:file_search_path(myapp, Tok)), format(atom(Coder), '~s/src/coder', [Dir]), asserta(user:file_search_path(myapp, Coder)). ``` If there’s a shorter cleaner way I’d love to know by the way! 🙂 In my main ast.pl file I have included the module that contains the extracted code, now under a common predicate name of `inst//2` for -instruction- as that’s what they are processing. My main ast file: ```prolog :- multifile inst//2. :- use_module(myapp(defun)). ``` and in my defun.pl file which lives in `src/ast/inst/defun.pl` I have this at the top of the file: ```prolog :- module(myapp(defun)). :- multifile inst//2. inst( ..... ) --> ....code.,.... ``` When I step through the code, at the point of calling it, it immediately fails, it doesn’t even seem to try calling into the imported module. When I execute `listing(inst)` I can see that the code in both files present: ```prolog :- multifile ast:inst/4. :- multifile defun:inst/4. defun:inst(defun(Pos), : defun:inst('defun+'(Pos), : defun:inst('defun#'(Pos), : : etc. ``` The call site is: ```prolog built_in_func(Out) --> [Term], { Term =.. [Fn, _Pos], reserved_word(Fn), bifmap(Fn, RealFn), debug(ast, "built_in_func: calling as: ~w", [inst(Term,Out)]) }, inst(Term, Out). % <-- fails immediately % call(RealFn, Start, Out). ``` and the code I expected to be called is: ```prolog :- module(defun, [inst//2]). :- multifile inst//2. inst(defun(Pos), defun(Pos, pub(Name), Args, Body)) --> defun_(defun_function_name, Pos, Name, Args, Body). : : much more code... ``` This is the first time I have tried to split my code out like this but it means I can write tests in the same file now they are going to be small little units of brilliantly logically beautiful code… 😑 So, what have I done wrong / not done in order to break out a large file into smaller files and use the module system? Thank you in advance, Sean. ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 2:39pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/2 "2021-04-05T14:39:01Z")
OK, After posting, you always remember -something- you read somewhere… for me it was remembering the extended module:predicate calling format so for now, I have modified my code to look like this, using the functor name as the module name, which isn’t such a hardship and would actually enforce the rule of one module per reserved word handler which is fine. Heck, maybe this -is- the answer I was looking for ? ```prolog built_in_func(Out) --> [Term], { Term =.. [Fn, _Pos], reserved_word(Fn), bifmap(Fn, RealFn), debug(ast, "built_in_func: calling as: ~w", [inst(Term,Out)]) }, RealFn:inst(Term, Out). % call individual handler! eg defun:inst() ``` This means at least that I can continue to break the code out into separate file in lieu of a more pertinent answer. ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 3:03pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/3 "2021-04-05T15:03:24Z")
OK, well, I’ve stopped doing that pattern as the number of warnings is growing with each one I farm out: ```prolog | Warning: /Users/sean/Documents/code/prolog/the-f-word-project/src/ast/ast.pl:37: Warning: Local definition of ast:inst/4 overrides weak import from assign Warning: /Users/sean/Documents/code/prolog/the-f-word-project/src/ast/ast.pl:38: Warning: Local definition of ast:inst/4 overrides weak import from defun Warning: /Users/sean/Documents/code/prolog/the-f-word-project/src/ast/ast.pl:39: Warning: Local definition of ast:inst/4 overrides weak import from defvar Warning: /Users/sean/Documents/code/prolog/the-f-word-project/src/ast/ast.pl:40: Warning: Local definition of ast:inst/4 overrides weak import from emit ``` So what -is- the best way to break out a large file into smaller ones ? ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 3:23pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/4 "2021-04-05T15:23:09Z")
Thanks again to @pmoura and he doesn’t even know it yet! 🙂 I dived in and found this article: [http://swi-prolog.996271.n3.nabble.com/About-quot-multifile-quot-td6839.html](http://swi-prolog.996271.n3.nabble.com/About-quot-multifile-quot-td6839.html) The nugget of hope was shown and I now have a fully working solution, no warnings or other flies in the ointment and I can now happily break up my code. Here is my solution thanks due to that article: in may MAIN ast file: ```prolog :- multifile ast:inst//2. :- use_module(myapp(assign)). :- use_module(myapp(defun)). :- use_module(myapp(defvar)). :- use_module(myapp(emit)). ``` and then in my other files, a few packed in here… ```prolog :- module(defun, [ast:inst//2]). :- multifile ast:inst//2. ast:inst(defun(Pos), defun(Pos, pub(Name), Args, Body)) --> defun_(defun_function_name, Pos, Name, Args, Body). :- module(emit, [ast:inst//2]). :- multifile ast:inst//2. ast:inst(emit(Pos), emit(Pos, Terms)) --> all_single_or_sexp(Terms). : : etc. : ``` As those great scholars Bill and Ted would say, “Excelleeeennnnt!” As with APL, it does what you expect, you just have to know what to expect! Thanks Paulo! ---
**Author:** ![Boris](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/boris/32/7486_2.png) [@Boris](https://swi-prolog.discourse.group/u/Boris)\ **Post date:** [April 5, 2021, 3:36pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/5 "2021-04-05T15:36:31Z")
Paulo got too annoyed once and he left this list ☹ ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 3:37pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/6 "2021-04-05T15:37:38Z")
Noooooooo! Really? ---
**Author:** ![PaulBrownMagic](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/paulbrownmagic/32/211_2.png) [@PaulBrownMagic](https://swi-prolog.discourse.group/u/PaulBrownMagic)\ **Post date:** [April 5, 2021, 3:58pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/7 "2021-04-05T15:58:05Z")
Glad you got your across module predicates sorted. Regarding doing this in a cleaner way: ``` :- multifile user:file_search_path/2. :- prolog_load_context(directory, Dir), asserta(user:file_search_path(myapp, Dir)), format(atom(Src), '~s/src', [Dir]), asserta(user:file_search_path(myapp, Src)), format(atom(Ast), '~s/src/ast', [Dir]), asserta(user:file_search_path(myapp, Ast)), format(atom(Inst), '~s/src/ast/inst', [Dir]), asserta(user:file_search_path(myapp, Inst)), format(atom(Tok), '~s/src/tokeniser', [Dir]), asserta(user:file_search_path(myapp, Tok)), format(atom(Coder), '~s/src/coder', [Dir]), asserta(user:file_search_path(myapp, Coder)). ``` You could do this instead: ``` :- prolog_load_context(directory, Dir), asserta(user:file_search_path(myapp, Dir)), asserta(user:file_search_path(src, myapp(src))), asserta(user:file_search_path(ast, src(ast))), asserta(user:file_search_path(inst, ast(inst))), asserta(user:file_search_path(tokeniser, src(tokeniser))), asserta(user:file_search_path(coder, src(coder))). ``` Using this means you’ll need to be more explicit with your imports: ``` :- multifile ast:inst//2. :- use_module(myapp(assign)). % I can't see where this actually is :- use_module(inst(defun)). :- use_module(inst(defvar)). :- use_module(myapp(emit)). % I can't see where this actually is ``` This has the advantage that your code tells you about where the file is, so when you’re looking for it somewhere in `myapp`, you at least know what directory it’s in and you’re only a query away from getting the whole path to it, rather than searching. ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 4:00pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/8 "2021-04-05T16:00:06Z")
Thanks Paul, I’ll study that and decide if I go with it ot now…it does look a lot cleaner though at the cost of being clearer about imports as you say. Thanks. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [April 5, 2021, 4:38pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/9 "2021-04-05T16:38:09Z")
Better. Note that you only have to assert the one that you compute dynamically from prolog\_load\_context/2. The others can just be facts in the file. You can also dynamically add (say) `myapp_root` as dynamically computed alias and then do ```prolog user:file_search_path(myapp, myapp_root(src)). user:file_search_path(myapp, myapp_root(src/ast)). ... ``` Does it make much sense to use a directory structure and then smash these directories to the same alias in Prolog, creating a flat namespace? I also have my doubt that multifile is a nice solution. If you can avoid it, that is typically a good idea. ---
**Author:** ![emacstheviking](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/emacstheviking/32/228_2.png) [@emacstheviking](https://swi-prolog.discourse.group/u/emacstheviking)\ **Post date:** [April 5, 2021, 7:23pm UTC](https://swi-prolog.discourse.group/t/multifile-and-dcg-rules-being-stubborn-predicate-fails-immediately/3796/10 "2021-04-05T19:23:13Z")
I don’t like `multifile/2` either it feels somehow kludgy but I can’t think of another way, being something of a newcomer to the environment. Is there some glaringly obvious feature I have missed? I’ve spent a (comparatively) long time for me learning Prolog thus far but I have not really picked up too much about the SWI environment. I had a heck of a time when trying some of the http server stuff for instance. I will study your comment in depth regarding expressing the search path as facts, for whatever reason I sometimes find the official docs either confusing or unclear to my beginner and it puts me at odds with what I am trying to do until I finally get it, usually after much gnashing of teeth etc. Thanks.