<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> </head> <body> Fellow beginner - so I possibly should not answer:). If you change the modes for the `fill` predicate back to `::sdi` and `::suo` and comment out `has_n(N2, !State)` then your code runs (attached). I suggest that the error for `hash_table.det_insert/4` has to do with writing the same values to an existing hash table (in parallel?) - but that explanation seems lacking, as the sequential tests are okay. For the code, I also introduced a State variable - but that seems to be more a matter of style. -- Mark <div class="moz-cite-prefix">On 23/07/2021 03:27, Ricardo Correia wrote: </div> <blockquote type="cite" cite="mid:YPobBrpJQzODjF3N@wizylap.wizy.org"> <pre class="moz-quote-pre" wrap="">Hi, I'm a Mercury beginner that is trying to learn the language and I'm not yet familiar with most of the Prolog/Mercury terminology, so please bear with me :) I have attached a Mercury program which is failing at runtime with an exception due to what seems to be a known compiler bug, but I'm not entirely sure. I have a `state` type which is composed of two integers and a hash table. Since it has a hash table, variables of this type should be unique, I assume, so that the program doesn't backtrack with respect to the contents of the hash table. However, I'm not entirely sure how to make type `state` unique. I've tried simply using the ::di and ::uo modes, but then fill/3 fails to compile the call to `hash_table.det_insert/4`, although I don't understand exactly why. Then, I tried to do what the `hash_table` standard library module does, I think, by declaring an instantiation (?) and some custom `sdi` and `suo` modes, because `hash_table` is also a type which has some integers and a vector (which also has to be unique) so I assumed my type was similar enough. This compiled fine but then the program fails with an exception because (as far as I can see) when backtracking, the integer fields within the `state` type do backtrack but the hash table doesn't. I am guessing that this is related to the first limitation mentioned in the `LIMITATIONS` file and in the hash table module -- specifically, that the Mercury compiler doesn't handle nested unique modes yet. Although, even if this is true, I am disappointed that the Mercury compiler didn't give me a warning or an error when compiling and allowed my program to misbehave at runtime. My questions are: 1. Is my understanding above correct? 2. Are there still plans to fix nested unique modes? Also, is this something that is being worked on? 3. Is there a way to still use hash tables or vectors within other types somewhat safely, i.e. in a way that the compiler warns if the code may backtrack unexpectedly, like it usually happens with the `io` type? Also, I should mention that as a beginner and even after reading both tutorials and some of the reference manual, I find that the LIMITATIONS file is extremely unclear with respect to the first limitation. These are the issues in the first limitation that I am struggling with: 1. It says that "definite aliasing" is "not allowed", however I still don't quite understand what "definite aliasing" is or what "is not allowed" means (does the compiler give a warning or error in this case or is the program simply miscompiled?). 2. It says that "partial instantiation" and "nested unique modes" are "unusable", but again, it doesn't explain what "partial instantiation" means nor what "unusable" means in this case. Again, does the compiler give a warning or error or is the program simply miscompiled? 3. It then gives a detailed explanation, but I'm not sure if the detailed explanation refers to the whole "definite aliasing" limitation or only to the "partial instantiation working by chance" issue. 4. The detailed explanation talks about scope, but again I don't know what scope means in this case (what other scopes are there?) 5. It refers to Mantis bug 311, which seems to have nothing to do with nested unique modes, I think. The attached program which exhibits the error in bug 311 *does* generate a compiler warning, but not my attached program. 6. The first limitation would be much clearer if there were some examples of code which works (including the special case mentioned in the detailed explanation) and code which should work but doesn't (and whether it doesn't because the compiler fails or because the program will misbehave at runtime). Thanks! </pre> <fieldset class="mimeAttachmentHeader"></fieldset> <pre class="moz-quote-pre" wrap="">_______________________________________________ users mailing list <a class="moz-txt-link-abbreviated" href="mailto:users@lists.mercurylang.org">users@lists.mercurylang.org</a> <a class="moz-txt-link-freetext" href="https://lists.mercurylang.org/listinfo/users">https://lists.mercurylang.org/listinfo/users</a> </pre> </blockquote> </body> </html>