<div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif">I'm sorry Arnaud, but my brain is insufficiently large to accommodate the implications of five different briefly specified options. Would you (or Shea) like to specify them more precisely, perhaps on GH since email threads are harder to follow (and it allows others to contribute). I think it would help to give some examples to illustrate the consequences of each.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Here's the kind of thing I mean (below).</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Also can we check with Shea that he is content with these options? It's his proposal</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Simon</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">
<div class="gmail_default" style="font-family:tahoma,sans-serif">module Ex1 where { ..; main :: IO Void }</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif">module Ex2 where { ..; main :: IO () }</div>
module Ex3 where { ..; main :: IO Int }</div><div class="gmail_default" style="font-family:tahoma,sans-serif">module Ex4 where { ...; main :: IO ExitCode } -- ExitCode exists already</div><div class="gmail_default" style="font-family:tahoma,sans-serif">module Ex5 where { ...; main :: IO Bool } -- No ExitStatus instance for Bool<br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">module Ex6 where { ...; data T = ..; main :: IO T; instance ExitStatus T where ... }</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><b>Option 1:
a warning when main isn't at type IO () or IO Void</b><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><ul><li>A warning on Ex3-6.</li><li>Ex4 returns exit code 0<br></li><li>Is this warning on by default? Can it be suppressed? (Rather than provide -Wnoxxx flag, we could just say "change the code to return ()"</li></ul><div><b>Option 2:
New type-class-based behaviour without extension
</b></div></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><ul><li>Ex1,2,4.6 work fine</li><li>Ex4 returns the specified exit code.</li><li>Ex3, and Ex5 yields "no instance for ExitStatus Int" (and Bool resp)</li></ul><div><b>Option 2a: Like Option 2 but with warning</b></div><div><ul><li>Ex3 and Ex5 yield a warning not at error; but run fine<br></li></ul></div><div>
<div><b>Option 3:
New type-class-based behaviour with extension <br></b></div><div><ul><li>Without -XWombat: like Option 1</li><li>With -XWombat: like Option </li></ul><div>
<div><b>Option 3a: Like Option 3 but with warning</b></div><div><ul><li>
With -XWombat, Ex3 and Ex5 yield a warning not at error; but run fine
</li></ul></div>
</div></div>
</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, 26 Mar 2024 at 09:35, Arnaud Spiwack <<a href="mailto:arnaud.spiwack@tweag.io">arnaud.spiwack@tweag.io</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Alright, so here are the plausible alternatives</div><div><br></div><div>1a. New type-class-based behaviour without extension</div><div>1b. New type-class-based behaviour gated by an extension</div><div>2. Just a warning (when main isn't at type IO () or IO Void)</div><div>3a. A warning + the new type-class-based behaviour gated by an extension. With the extension, types that don't implement the type class raise an error.</div><div>3b. A warning + the new type-class-based behaviour gated by an extension.
With the extension, types that don't implement the type class raise a warning (which could have a different phrasing than without the extension).</div><div><br></div><div>Let's vote!<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, 22 Mar 2024 at 15:30, Malte Ott <<a href="mailto:malte.ott@maralorn.de" target="_blank">malte.ott@maralorn.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On 2024-03-22 08:58, Arnaud Spiwack wrote:<br>
> @Malte, in my opinion, with the extension on, types which are not covered<br>
> by the type class should error out.<br>
<br>
Ah, I see. Well, I am fine either way.<br>
<br>
I just don’t see much value in deciding for the user which code problems are<br>
unacceptable. Especially since this will make the corresponding language<br>
extension more breaking and thus harder to make the default.<br>
Others have voiced similar opinions in the GitHub thread.<br>
<br>
Best<br>
Malte<br>
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</blockquote></div><br clear="all"><br><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr">Arnaud Spiwack<br>Director, Research at <a href="https://moduscreate.com" rel="noopener noreferrer" target="_blank">https://moduscreate.com</a> and <a href="https://tweag.io" rel="noopener noreferrer" target="_blank">https://tweag.io</a>.</div></div>
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