<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=Windows-1252"> </head> <body> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> Julien: thank you for this. Your mercury-java library has been a key resource.</div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> <br> </div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> I have submitted a pull request (https://github.com/Mercury-Language/mercury/pull/139) that adds generic types to the "extends" clause, which addresses mve.m. This means that we can write Java code to catch exceptions and write them to Mercury types (from Java).</div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> <br> </div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> By my understanding, we would need to add generic types for "new" Mercury types which have generic types (e.g. as per mve2.m and mve3.m). This is not addressed by the submitted pull request.</div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> <br> </div> <div dir="auto" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;"> ---- Mark</div> <div id="ms-outlook-mobile-body-separator-line" data-applydefaultfontstyles="true" style="font-family: Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif; font-size: 12pt;" dir="auto"> <br> </div> <div style="font-family:Aptos, Aptos_MSFontService, -apple-system, Roboto, Arial, Helvetica, sans-serif;font-size:12pt" dir="auto" id="ms-outlook-mobile-signature"> </div> <hr style="display:inline-block;width:98%" tabindex="-1"> <div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Julien Fischer <jfischer@opturion.com><br> <b>Sent:</b> Friday, September 19, 2025 3:27:19 PM<br> <b>To:</b> Mark Clements <mark.clements@ki.se><br> <b>Cc:</b> users@lists.mercurylang.org <users@lists.mercurylang.org><br> <b>Subject:</b> Re: [m-users.] Java exceptions and nested classes</font> <div> </div> </div> <div class="BodyFragment"><font size="2"><span style="font-size:11pt;"> <div class="PlainText">[You don't often get email from jfischer@opturion.com. Learn why this is important at <a href="https://aka.ms/LearnAboutSenderIdentification">https://aka.ms/LearnAboutSenderIdentification</a> ]<br> <br> Hi Mark,<br> <br> On Fri, 19 Sept 2025 at 21:05, Mark Clements <mark.clements@ki.se> wrote:<br> ><br> > I am investigating using JDBC with Mercury. Most of the JDBC classes throw an SQLException, which I want to catch in Java and return a result type with either an ok() value or an error(). I have the following minimal example (not using JDBC):<br> ><br> > :- module mve.<br> > :- interface.<br> > :- import_module io, int.<br> > :- type result(T,E) ---> ok(T) ; error(E).<br> > :- type exception.<br> > :- pred some_pred(int::in, mve.result(int,exception)::out, io::di, io::uo) is det.<br> > :- pred main(io::di, io::uo) is det.<br> > :- implementation.<br> > :- pragma foreign_type("Java", exception, "java.lang.Exception").<br> > :- pragma foreign_proc("Java",<br> > some_pred(A::in, C::out, _IO0::di, _IO1::uo),<br> > [will_not_call_mercury, thread_safe, promise_pure],<br> > "try {<br> > C = new Result_2.Ok_1<Integer,java.lang.Exception>(A);<br> > } catch(java.lang.Exception e) {<br> > System.err.println(e.getMessage());<br> > C = new Result_2.Error_1<Integer,java.lang.Exception>(e);<br> > }").<br> > main(!IO) :-<br> > some_pred(1, C, !IO),<br> > (C = ok(_) ; C = error(_)).<br> ><br> > However, when I compile this I get warnings, such as:<br> ><br> > mve.m:15: warning: [unchecked] unchecked conversion<br> > C = new Result_2.Ok_1<Integer,java.lang.Exception>(A);<br> > ^<br> > required: Result_2<Integer,Exception><br> > found: Ok_1<Integer,Exception><br> <br> Under the current compilation scheme for Java, you are not going to be able<br> to avoid those warnings. Mercury's use of generics in the Java grades is<br> rather limited. (Much of the generated code effectively works with raw types.)<br> <br> > Alternatively, is there a better way to catch the Java exceptions?<br> <br> I assume you mean: is there a better way to pass them back to Mercury?<br> (Obviously, the only way to catch them is to use the exception<br> handling mechanisms<br> that Java provides.)<br> <br> I would avoid relying on how Mercury represents types in Java and either use<br> exported functions to build the result terms (as per the attached<br> mve2.m example)<br> or just return a flag from the Java code indicating what has happened and deal<br> with constructing result terms in Mercury (as per the attached mve3.m example).<br> <br> (Some time ago I wrote <<a href="https://github.com/juliensf/mercury-java">https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fjuliensf%2Fmercury-java&data=05%7C02%7Cmark.clements%40ki.se%7C5ded018e0c9f4f336f8108ddf7804a55%7Cbff7eef1cf4b4f32be3da1dda043c05d%7C0%7C0%7C638938853514514300%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=67vstV8DKDJ%2BjI3onCJyWrbb3EoVUTvp2XgbhWtOekI%3D&reserved=0</a>>, which not<br> covering JDBC, may give you some idea for how to approach interfacing with<br> Java APIs.)<br> <br> Julien.<br> <br> <br> <br> <br> <br> <br> <br> <br> ><br> > --- Mark.<br> ><br> ><br> > När du skickar e-post till Karolinska Institutet (KI) innebär detta att KI kommer att behandla dina personuppgifter. 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You can read more about KI’s processing of personal data here<<a href="https://staff.ki.se/data-protection-policy">https://staff.ki.se/data-protection-policy</a>>.<br> > _______________________________________________<br> > users mailing list<br> > users@lists.mercurylang.org<br> > <a href="https://lists.mercurylang.org/listinfo/users">https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.mercurylang.org%2Flistinfo%2Fusers&data=05%7C02%7Cmark.clements%40ki.se%7C5ded018e0c9f4f336f8108ddf7804a55%7Cbff7eef1cf4b4f32be3da1dda043c05d%7C0%7C0%7C638938853514565787%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=lSTPQxf8lrNqHNC%2B%2BeSgu8o96ZR81THpbOogzCv3BCM%3D&reserved=0</a><br> </div> </span></font></div> </body> </html>