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Ziv: thank you for this suggestion. Note that I have raised an issue on UrLib on an unrelated matter.<br>
<br>
After some head-scratching, I got as far as:<br>
<br>
fun update_ab [write] (sub : Subset.t [A=int,B=int] write) (w : $write) =<br>
{A=1,B=2} --- write ++ w<br>
<br>
which also does not work. Any guidance here would be appreciated - I admit to being stuck after looking closely at UrLib's subset.ur(s) and magicTable.ur(s).<br>
<br>
Kindly, Mark.<br>
<br>
<div class="moz-cite-prefix">On 29/10/19 4:39 pm, Ziv Scully wrote:<br>
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<div dir="auto">One can capture subset constraints using a type class, as the following module does:</div>
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<div><a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fvizziv%2FUrLib%2Fblob%2Fmaster%2FUrLib%2Fsubset.urs&data=02%7C01%7Cmark.clements%40ki.se%7C46a639348ebc4f9a241108d75c865133%7Cbff7eef1cf4b4f32be3da1dda043c05d%7C0%7C0%7C637079604764017394&sdata=ueZ7e9P7Rzqhq7P4vuBDpbcq8QbIYA5i8vhL9%2BgCvEc%3D&reserved=0" originalsrc="https://github.com/vizziv/UrLib/blob/master/UrLib/subset.urs" shash="ENvCGgqgBiJEpzDFfA8wU93l14msjvZkhKg4mk4NLPeKV20o77pdYiHcdCAJttUEFBn1YonQY7txSi8OJPQOMh2lOMXfvdUG/YL2z+rhsyk7iGxqxtcpI8rjN43l+Xl4yQHFh/BspKaMv0UVzwLaFLIegmY7M7+R0YyIuJNx6qs=" moz-do-not-send="true">https://github.com/vizziv/UrLib/blob/master/UrLib/subset.urs</a></div>
<div><a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fvizziv%2FUrLib%2Fblob%2Fmaster%2FUrLib%2Fsubset.ur&data=02%7C01%7Cmark.clements%40ki.se%7C46a639348ebc4f9a241108d75c865133%7Cbff7eef1cf4b4f32be3da1dda043c05d%7C0%7C0%7C637079604764027387&sdata=RDT9vPh4qegdK9iiBr%2F2K7vpFc4z%2BF2y4cHa2eDe5Tw%3D&reserved=0" originalsrc="https://github.com/vizziv/UrLib/blob/master/UrLib/subset.ur" shash="OD1d0jf3kirUYjrxphwMoQB5brjhic+y47P6xQ0aRIWyX+26cWjdYgu9u2EARjyF32CYK6AjlfNhXavDhXTKEVQE+FmkbKpCEWcuk9NkAIYz9YnS9zwjw4kSCgWLzF9TbRaPD/Sm82C1kAWCl0rsDkDgrrttifDFwgKQDCGOiDA=" moz-do-not-send="true">https://github.com/vizziv/UrLib/blob/master/UrLib/subset.ur</a></div>
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<div dir="auto">(It relies on another module, Eq, from the same project.)</div>
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<div dir="auto">Ziv</div>
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<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Oct 29, 2019 at 11:21 Mark Clements <<a href="mailto:mark.clements@ki.se" moz-do-not-send="true">mark.clements@ki.se</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Adam: thank you for your prompt reply.<br>
<br>
To define defaultSettings properly, is there some way to constraint the<br>
type union (keep ++ change) to an existing type (e.g. {A:int, B:int})?<br>
The following also do not work:<br>
<br>
fun defaultSetting<br>
[keep] [change] [keep ~ change]<br>
(args : $change)<br>
: $(keep ++ change) =<br>
update {A=1, B=1} args<br>
<br>
(* or *)<br>
<br>
fun defaultSetting<br>
[keep] [change] [keep ~ change]<br>
(args : $change)<br>
: $(keep ++ change) =<br>
{A=1,B=1} --- change ++ args<br>
<br>
-- Mark<br>
<br>
On 29/10/19 12:52 am, Adam Chlipala wrote:<br>
> On 10/28/19 3:27 PM, Mark Clements wrote:<br>
>> fun defaultSetting args =<br>
>> update {A=1, B=1} args<br>
>><br>
>> val _ = defaultSetting {A=2} (* {A=2, B=1} *)<br>
>> val _ = defaultSetting {B=2} (* {A=1, B=2} *)<br>
> The problem is that polymorphism in Ur/Web is always declared<br>
> explicitly, not inferred as OCaml or Haskell. You must add binders<br>
> for type variables for defaultSettings just as you did for update.<br>
> (This statement applies to definitions of functions, not uses, so the<br>
> two example calls above should work once you get defaultSettings<br>
> defined properly.)<br>
<br>
<br>
<br>
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