# Phrase\_from\_file fails after 17 iterations **URL:** \ **Category:** General\ **Created:** [June 8, 2023, 1:52pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624 "2023-06-08T13:52:08Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![eddiec](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/eddiec/32/3846_2.png) [@eddiec](https://swi-prolog.discourse.group/u/eddiec)\ **Post date:** [June 8, 2023, 1:52pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/1 "2023-06-08T13:52:08Z")
Hi, having an odd problem calling _phrase\_from\_file_ in a loop. consulted file: ```prolog get_neighbors(FileName, NbrInfos):- phrase_from_file(device_neighbors(NbrInfos), FileName), !. ``` called as: ```prolog process_nbrs_file(Switch):- get_neighbors(Switch, NbrInfos), do_stuff_with(Switch,NbrInfos). main:- expand_file_name('*',Switches), forall(member(Switch,Switches), once(process_nbrs_file(Switch))). ``` Every file parses correctly individually but when called like this it stops on the 18th file. I was guessing maybe a limit of 20 file descriptors but I can’t find any reference to that. And _phrase\_from\_file_ calls _close_ (inside cleanup). What I see when debugging is that _device\_neighbors_ when called on the 18th time gets an empty list as the DCG tail. I can do them individually but there are hundreds so it slows the process down. Happens on 9.0.4 and 8.4.2 Any help appreciated. ---
**Author:** ![brebs](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@brebs](https://swi-prolog.discourse.group/u/brebs)\ **Post date:** [June 8, 2023, 2:35pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/2 "2023-06-08T14:35:04Z")
“Stops”? With what text output and/or exit code? Try running on just that 18th file. ---
**Author:** ![eddiec](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/eddiec/32/3846_2.png) [@eddiec](https://swi-prolog.discourse.group/u/eddiec)\ **Post date:** [June 8, 2023, 3:03pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/3 "2023-06-08T15:03:02Z")
Stops → fails. I’ve run it on all files and it succeeds if done individually. Since the DCG list is empty the 18th time it will fail to parse and hence fail the _forall_. ---
**Author:** ![brebs](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@brebs](https://swi-prolog.discourse.group/u/brebs)\ **Post date:** [June 8, 2023, 3:11pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/4 "2023-06-08T15:11:59Z")
Zero-in on the code line which fails, and determine _why_. Standard debugging. ---
**Author:** ![eddiec](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/eddiec/32/3846_2.png) [@eddiec](https://swi-prolog.discourse.group/u/eddiec)\ **Post date:** [June 8, 2023, 3:14pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/5 "2023-06-08T15:14:17Z")
There aren’t any lines that fail. The parse works when done individually. The debugging tells me that the contents of the file is missing. ---
**Author:** ![brebs](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@brebs](https://swi-prolog.discourse.group/u/brebs)\ **Post date:** [June 8, 2023, 4:06pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/6 "2023-06-08T16:06:58Z")
If it fails, as you said, then it fails at a particular point. So, identify that point. This is standard debugging. ---
**Author:** ![eddiec](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/eddiec/32/3846_2.png) [@eddiec](https://swi-prolog.discourse.group/u/eddiec)\ **Post date:** [June 8, 2023, 4:39pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/7 "2023-06-08T16:39:22Z")
I’ve identified the failure 3 times now! When _phrase\_from\_file_ calls _device\_neighbors_ the DCG list that should be the contents of the file is empty. It’s not failing in my code. Please read what I’ve written. I was hoping there would be some deep prology reason why it couldn’t open another file or something. On reflection, I’ll just submit a bug report. ---
**Author:** ![brebs](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@brebs](https://swi-prolog.discourse.group/u/brebs)\ **Post date:** [June 8, 2023, 6:51pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/8 "2023-06-08T18:51:14Z")
In your bug report, please include a [Minimal reproducible example - Wikipedia](https://en.wikipedia.org/wiki/Minimal_reproducible_example) ---
**Author:** ![EricGT](https://avatars.discourse-cdn.com/v4/letter/e/f1d935/32.png) [@EricGT](https://swi-prolog.discourse.group/u/EricGT)\ **Post date:** [June 8, 2023, 6:52pm UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/9 "2023-06-08T18:52:06Z")
> [@eddiec](#): > > I’ll just submit a bug report Sorry to say this but I really don’t see enough evidence here to support that you have found a bug. * * * > [@eddiec](#): > > `expand_file_name('*',Switches)` Some ideas. Have you tried using gtrace/0 to debug the code? e.g. ```prolog main:- gtrace, expand_file_name('*',Switches), forall(member(Switch,Switches), once(process_nbrs_file(Switch))). ``` 1. Did you closely read the documentation for expand\_file\_name/2 > Unify List with a sorted list of files or directories matching WildCard. I suspect that the list contains directories such as `.` and `..`, make sense? Can you show us what is in the list `Switches` before forall/2. ```prolog main:- expand_file_name('*',Switches), print_term(Switches,[]), forall(member(Switch,Switches), once(process_nbrs_file(Switch))). ``` I have not tried this but you should get the idea. use [file\_exists/1](https://www.swi-prolog.org/pldoc/doc_for?object=file_systems%3Afile_exists/1) ```prolog :- use_module(library(file_systems)). main:- expand_file_name('*',Switches), print_term(Switches,[]), forall( member(Switch,Switches), ( file_exists(Switch), once(process_nbrs_file(Switch)) ; true ) ). ``` ---
**Author:** ![eddiec](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/eddiec/32/3846_2.png) [@eddiec](https://swi-prolog.discourse.group/u/eddiec)\ **Post date:** [June 9, 2023, 8:55am UTC](https://swi-prolog.discourse.group/t/phrase-from-file-fails-after-17-iterations/6624/10 "2023-06-09T08:55:24Z")
No, there’s no bug, not in swipl (not in my code either). A couple of the input files had been truncated and it never occured to me to check for that before running it. I was using gtrace, but I’ve never been able to navigate the stack without getting lost. Anway, it was a stupid mistake not to look outside the code. Somehow those are usually the ones that end up embarassing me.