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<p class="msipheader7557e74b" align="Left" style="margin:0"><span style="font-size:9.0pt;font-family:Arial;color:#317100">PUBLIC</span></p>
<br>
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">I am trying to typecheck & load three modules using the GHC API. The first one defines a class, the second one defines an instance of said class, and the third one uses the instance
(attached as Class.src, Instance.src and Use.src, respectively). The problem is that when I typecheck Use.src, it complains about the missing instance. It should be noted that the class is found, only the instance isn’t.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">My code is bypassing the normal GHC driver to feed it modules instead of letting GHC itself come up with dependencies and then loading them from disk; that is because in my real
use case, some dependencies will have interfaces generated on the fly (there is no underlying Haskell source code), or loaded over HTTP, etc. So I am using parseModule and typeCheckModule on each module, make a ModIface from each, and then I try to register
them with GHC, by extending the HPT, the moduleNameProvidersMap, and the EPS. Evidently, this is not enough, and the instances should be registered somewhere else as well – where is that place?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">I have attached a simplified version of my code as Main.hs; it is targeting the GHC 9.0 API. It hardcodes the GHC 9.0 package.conf.d due to laziness on my part; please change
line 96 to your environment before running it. As written, it fails when typechecing Use.src with:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">input/Use.src:7:7: error:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> • No instance for (C X) arising from a use of ‘method’<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> • In the expression: method<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> In an equation for ‘foo’: foo = method<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> |<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console"">7 | foo = method<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Lucida Console""> | ^^^^^^<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"> Gergo<o:p></o:p></span></p>
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