<html><head><meta http-equiv="content-type" content="text/html; charset=us-ascii"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div><font face="FiraCode-Regular">[A] :- type callback == (pred(world, world, io, io)).</font></div><div><font face="FiraCode-Regular">[B] :- inst callback == (pred(in, out, di, uo) is det).</font></div><div><font face="FiraCode-Regular"><br></font></div><div><font face="FiraCode-Regular">[C] :- pred run_loop(</font></div><div><font face="FiraCode-Regular"> callback::in(callback), world::in, world::out, io::di, io::uo</font></div><div><font face="FiraCode-Regular"> ) is det.</font></div><div><br></div><div>In an attempt to demystify it all then, at point [A] I am defining an equivalence type which is merely a Mercury way of defining something similar to a C preprocessor macro in that the use of callback *as a type* specified will just cause the compiler to use the value on the right hand side of '=='. That much I understand, I think!</div><div><br></div><div>At [B], I am defining an instantiatedness tree, that although it has the same name as that used at [A], bears no actual relationship to it in any way.</div><div><br></div><div>At [C], I am declaring that run_loop/5 is a predicate that takes an argument of *type* callback, and that that it is an input, and that the input MUST have the instantiatedness defined by the definition at [B], the first use of callback being the type, and the in(callback) is stating that the value MUST be ground i.e. contain no free variables.</div><div><br></div><div>Is that not even wrong, or close?</div><div><br></div><div>Despite it making me feel dumber than dumb, I continue to love Mercury for all that it offers! I did not have the luxury of doing a 'comp-sci degree' in my youth, I am self-taught which, whilst fun, can at times be so desparately discouraging when the manual content is written in such high-level language. If it wasn't for the high calibre and warmth of this mailing list I think I may have given up in my first month with mercury, a few years ago now!</div><div><br></div><div><div>:D</div><div><br></div><div>Thanks.</div></div><div><br></div><div><br></div><div><br><blockquote type="cite"><div>On 17 Jul 2023, at 16:07, Volker Wysk <post@volker-wysk.de> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Am Montag, dem 17.07.2023 um 15:52 +0100 schrieb Sean Charles</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">(emacstheviking):</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><blockquote type="cite" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">Zoltan, Volker...... yes!<br><br>That makes it compile and run just fine.... I am not sure I fully comprehend but I will go and RTFM some more, that might help.<br></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">"in" is an abbreviation for "in(ground)". "ground" means normal data,</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">nothing callable. A predicate isn't ground. Its inst is like you have</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">defined it in your ":- inst callback == ...".</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Cheers,</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Volker</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><blockquote type="cite" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br>Thank you both.<br><br><br><blockquote type="cite">On 17 Jul 2023, at 15:37, Zoltan Somogyi <zoltan.somogyi@runbox.com> wrote:<br><br><br>On 2023-07-17 16:27 +02:00 CEST, "Sean Charles (emacstheviking)" <objitsu@gmail.com> wrote:<br><blockquote type="cite">:- type callback == (pred(world, world, io, io)).<br>:- inst callback == (pred(in, out, di, uo) is det).<br><br>:- pred run_loop(<br> callback::in, world::in, world::out, io::di, io::uo<br>) is det.<br></blockquote><br>Without compileable example code I cannot be sure, but I think<br>the problem is the "callback::in" in the declaration of run_loop.<br>What happens when you replace it with "callback:in(callback)"?<br>The mode checker needs this to tell it the mode of the higher order arg.<br><br>Zoltan.<br></blockquote><br>_______________________________________________<br>users mailing list<br><a href="mailto:users@lists.mercurylang.org">users@lists.mercurylang.org</a><br><a href="https://lists.mercurylang.org/listinfo/users">https://lists.mercurylang.org/listinfo/users</a><br></blockquote><br style="caret-color: rgb(0, 0, 0); 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