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<p class="MsoNormal"><span style="font-size:12.0pt">Ranjit<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Have you read Note [The equality types story] in compiler/prelude/TysPrim?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">As you’ll see (~) is actually a class; the equality predicate is (~#).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">There doesn’t seems to be a named-function predicate that checks for it explicitly, but if you grep for eqTyCon you’ll see lots of tests for it. I’m sure these tests could be tideied up into a smaller collection
of predicates.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> rjhala@eng.ucsd.edu [mailto:rjhala@eng.ucsd.edu]
<b>On Behalf Of </b>Ranjit Jhala<br>
<b>Sent:</b> 09 February 2018 04:41<br>
<b>To:</b> Simon Peyton Jones <simonpj@microsoft.com><br>
<b>Subject:</b> Re: about GHC API: Looking up names<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<span style="font-family:"Courier New"">Dear Simon, <br>
<br>
still working on the above, but hit an odd problem on the way.<o:p></o:p></span></p>
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<span style="font-family:"Courier New"">How can I "test for" (i.e. write a function of type `Type -> Bool`)
<br>
that returns `True` for values (i.e. `Type`s) that print out as:<br>
<br>
typ ~ <a href="https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2FGHC.Types.Int&data=04%7C01%7Csimonpj%40microsoft.com%7C29c2e5ecd0f04842953508d56f774eca%7Cee3303d7fb734b0c8589bcd847f1c277%7C1%7C0%7C636537480568476914%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwifQ%3D%3D%7C-1&sdata=KKRza3vDtm0mAlSP%2F4XzltIh5XqGlc9CY3tAXrUzF10%3D&reserved=0">
GHC.Types.Int</a><o:p></o:p></span></p>
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<span style="font-family:"Courier New"">or with, which some more detail, looks like<o:p></o:p></span></p>
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<span style="font-family:"Courier New""><br>
(~ (TYPE LiftedRep) typ <a href="https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2FGHC.Types.Int&data=04%7C01%7Csimonpj%40microsoft.com%7C29c2e5ecd0f04842953508d56f774eca%7Cee3303d7fb734b0c8589bcd847f1c277%7C1%7C0%7C636537480568476914%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwifQ%3D%3D%7C-1&sdata=KKRza3vDtm0mAlSP%2F4XzltIh5XqGlc9CY3tAXrUzF10%3D&reserved=0">
GHC.Types.Int</a>)<o:p></o:p></span></p>
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<span style="font-family:"Courier New"">I would have thought that `Type.isEqPred` or `Type.isNomEqPred`<o:p></o:p></span></p>
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<span style="font-family:"Courier New"">described here <br>
<br>
<a href="https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.haskell.org%2F~ghc%2F8.2.1%2Fdocs%2Fhtml%2Flibraries%2Fghc-8.2.1%2Fsrc%2FType.html%23isEqPred&data=04%7C01%7Csimonpj%40microsoft.com%7C29c2e5ecd0f04842953508d56f774eca%7Cee3303d7fb734b0c8589bcd847f1c277%7C1%7C0%7C636537480568476914%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwifQ%3D%3D%7C-1&sdata=sM%2F3Xje4uR3MLwy4wHY28RWqiyq9JauXXO1lrHAgiYs%3D&reserved=0">
https://downloads.haskell.org/~ghc/8.2.1/docs/html/libraries/ghc-8.2.1/src/Type.html#isEqPred</a><o:p></o:p></span></p>
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<span style="font-family:"Courier New"">would work, but apparently not?<o:p></o:p></span></p>
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<span style="font-family:"Courier New"">Any clues? Thanks!<o:p></o:p></span></p>
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<span style="font-family:"Courier New"">- Ranjit.<o:p></o:p></span></p>
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<span style="font-family:"Courier New""><o:p> </o:p></span></p>
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<o:p> </o:p></p>
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On Thu, Feb 1, 2018 at 8:25 AM, Ranjit Jhala <<a href="mailto:jhala@cs.ucsd.edu" target="_blank">jhala@cs.ucsd.edu</a>> wrote:<o:p></o:p></p>
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<span style="font-family:"Courier New"">Will do! Best, Ranjit.<o:p></o:p></span></p>
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<o:p> </o:p></p>
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On Thu, Feb 1, 2018 at 5:20 AM, Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">I’m glad you are un-glued, but it smells wrong to me and your solution seems like a workaround for a bug, not the Right Path.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Could you make a ticket with a repro case?</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Thanks!</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Simon</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US">From:</span></b><span lang="EN-US">
<a href="mailto:rjhala@eng.ucsd.edu" target="_blank">rjhala@eng.ucsd.edu</a> [mailto:<a href="mailto:rjhala@eng.ucsd.edu" target="_blank">rjhala@eng.ucsd.edu</a>]
<b>On Behalf Of </b>Ranjit Jhala<br>
<b>Sent:</b> 31 January 2018 19:14<br>
<b>To:</b> Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>><br>
<b>Subject:</b> Re: about GHC API: Looking up names</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">Dear Simon,</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">No worries, I was able to figure it out, or at least work around it.</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-size:12.0pt;font-family:"Courier New"">></span><span style="font-family:"Courier New"">
</span><span style="font-size:12.0pt;font-family:"Courier New"">It’s very mysterious that declaring it in an
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-size:12.0pt;font-family:"Courier New"">> instance decl would make any difference.</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">It looks like that is exactly what is happening, but perhaps by design?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">(I saw there was something called an `ImplicitTyThing` that are not</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">in the top-level scope, so I figured that perhaps these instance</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">declarations were "implicit" and hence not available?)</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">Nevertheless, I was able to work around the issue by using
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> `tcGetFamInstEnvs`</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">to get the
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> `FamInstEnv`
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">and from that, making my own lookup environment (comprising the TyCon
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">and DataCon for the family instances.) This works for my purposes, but
</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">if the above is a possible bug, I can try to make a small test case?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">Thanks!</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New"">- Ranjit.</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">On Wed, Jan 31, 2018 at 1:47 AM, Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Hi Ranjit</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">That does sound odd. You should ask on ghc-devs too… though you may already have done that.
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Courier New"">hscTcRnLookupName
</span><span style="font-size:12.0pt">doesn’t do anything fancy: it just looks up the Name in the type environment. It’s very mysterious that declaring it in an instance decl would make any difference.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">I suppose you could somehow have gotten hold of the wrong Name.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">If I was debugging it, I’d start spitting out traces showing the type environment it is looking up in, to see what is there and what is not. If
you make a small standalone test case (e.g. a tiny client of the GHC API that demonstrates the problem) that could enable others to reproduce and help you. Or, I guess, we could do a Skype chat with you trying things locally.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">I wish I could help more</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Simon</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US">From:</span></b><span lang="EN-US">
<a href="mailto:rjhala@eng.ucsd.edu" target="_blank">rjhala@eng.ucsd.edu</a> [mailto:<a href="mailto:rjhala@eng.ucsd.edu" target="_blank">rjhala@eng.ucsd.edu</a>]
<b>On Behalf Of </b>Ranjit Jhala<br>
<b>Sent:</b> 26 January 2018 02:12<br>
<b>To:</b> Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>><br>
<b>Subject:</b> Q: about GHC API: Looking up names</span><o:p></o:p></p>
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<p><span style="font-family:"Courier New"">Dear Simon,</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">I have a question about the GHC API I wonder you can help with?</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Suppose `Library.hs` is has the constructors defined in the simple</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">top-level style:</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">```</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">data EntityField typ where</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">BlobXVal :: EntityField Int</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">BlobYVal :: EntityField Int</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">```</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Then when analyzing `Client.hs` (that imports `Library`), the lookup</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">function `hscTcRcLookupName` WORKS just fine to give me the `TyThing`
</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">corresponding to the name “BlobXVal”.</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">However, if instead, Library.hs defines the constructors within an instance:</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">```</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">instance PersistEntity Blob where</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">data EntityField Blob typ where</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">BlobXVal :: EntityField Blob Int</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">BlobYVal :: EntityField Blob Int</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">```</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">then, when analyzing Client.hs, the `hscTcRcLookupName` function FAILS to resolve the name.</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Clearly there is some difference in how `hscTcRcLookupName` works in these two cases.</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Does you know what it is?</span><o:p></o:p></p>
<p><span style="font-family:"Courier New""> </span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Thanks in advance!</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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