<div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">Hi Mark,<div><br></div><div>Here's how you'd write the function:</div><div><br></div></div></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div><div><font face="monospace">fun update_ab [write] (sub : Subset.t [A = int, B = int] write) (w : $write) =</font></div></div></div><div><div><font face="monospace"> Subset.elim</font></div><div><font face="monospace"> (fn [other] [write ~ other] _ _ pf =></font></div><div><font face="monospace"> Eq.cast (Eq.symm pf) [record]</font></div><div><font face="monospace"> (Eq.cast pf [record] {A = 1, B = 2} --- write ++ w))</font></div></div></blockquote><div dir="ltr"><div dir="ltr"><div><br></div><div>The basic idea is to use <font face="monospace">Subset.elim</font> to "unpack" sub. This gives you access to the type-level record <font face="monospace">other</font> and the value <font face="monospace">pf</font>, which allows you to cast between <font face="monospace">{A : int, B : int}</font> and <font face="monospace">$(write ++ other)</font>. You can't do this sort outside of the function passed to <font face="monospace">Subset.elim</font> because, among other reasons, you don't know what <font face="monospace">other</font> is.</div><div><br></div><div>That said, this seems like a lot of work for what is a pretty simple pattern, so I added some new functions to <font face="monospace">Subset</font> that should help.</div><div><br></div></div></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div style="color:rgb(0,0,0)"><font face="monospace">val set :</font></div><div style="color:rgb(0,0,0)"><font face="monospace"> fields ::: {Type} -> keep ::: {Type} -> t fields keep -></font></div><div style="color:rgb(0,0,0)"><span style="font-family:monospace"> $fields -></span></div><div style="color:rgb(0,0,0)"><font face="monospace"></font></div><div style="color:rgb(0,0,0)"><font face="monospace"> $keep</font></div><div style="color:rgb(0,0,0)"><span style="font-family:monospace"> -> $fields</span></div><div><font face="monospace"><br></font></div><div><font face="monospace">val over :</font></div></div><div><div><div><div><font face="monospace"> fields ::: {Type} -> keep ::: {Type} -> t fields keep -></font></div></div></div></div><div><div><div><div><font face="monospace"> ($keep -> $keep)</font></div></div></div></div><div><div><div><div><font face="monospace"> -> $fields -> $fields</font></div></div></div></div></blockquote><div dir="ltr"><div dir="ltr"><div><br></div><div>With either of these, your function is much simpler :).</div><div><br></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div style="color:rgb(0,0,0)"><font face="monospace">fun update_ab [write] (sub : Subset.t [A = int, B = int] write) (w : $write) =</font></div><div><font face="monospace" style="color:rgb(0,0,0)"> Subset.set </font><font color="#000000" face="monospace"><span style="caret-color: rgb(0, 0, 0);">{A = 1, B = 2} </span></font><span style="color:rgb(0,0,0);font-family:monospace">w</span></div></div><div style="color:rgb(0,0,0)"><font face="monospace"><br></font></div><div style="color:rgb(0,0,0)"><font face="monospace">fun update_ab [write] (sub : Subset.t [A = int, B = int] write) (w : $write) =</font></div><div style="color:rgb(0,0,0)"><font face="monospace"> Subset.over (fn _ => w) {A = 1, B = 2}</font></div></blockquote><div dir="ltr" style="color:rgb(0,0,0)"><div dir="ltr"></div></div><div><br></div><div>Hope that helps!</div><div><br></div><div>Best,</div><div>Ziv</div></div></div></div></div></div></div></div></div></div></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Dec 6, 2019 at 10:20 AM Mark Clements <<a href="mailto:mark.clements@ki.se" target="_blank">mark.clements@ki.se</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div>
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>On 29/10/19 4:39 pm, Ziv Scully wrote:<br>
</div>
<blockquote type="cite">
<div>
<div dir="auto">One can capture subset constraints using a type class, as the following module does:</div>
</div>
<div dir="auto"><br>
</div>
<div dir="auto">
<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" target="_blank">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" target="_blank">https://github.com/vizziv/UrLib/blob/master/UrLib/subset.ur</a></div>
<br>
</div>
<div dir="auto">(It relies on another module, Eq, from the same project.)</div>
<div dir="auto"><br>
</div>
<div dir="auto">Ziv</div>
<div dir="auto"><br>
</div>
<div><br>
<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" target="_blank">mark.clements@ki.se</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);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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