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<p class="MsoNormal">Generally, there is no assumption that binders are unique, anywhere in GHC.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The Simplifier does remove gratuitious shadowing (like (\x. \x. e)), but there is really no guarantee at any stage.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Simon<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs <ghc-devs-bounces@haskell.org>
<b>On Behalf Of </b>Csaba Hruska<br>
<b>Sent:</b> 08 May 2020 14:03<br>
<b>To:</b> GHC developers <ghc-devs@haskell.org><br>
<b>Subject:</b> Unique invariants: GHC invocation vs scope?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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Hello,<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
What are the intended invariants of Unique values?<o:p></o:p></p>
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So far I thought that it is always gives a unique identity to things during a whole GHC invocation. However this is not true. I.e. eta expansion breaks this assumption.<o:p></o:p></p>
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<o:p> </o:p></p>
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Here is a snippet from the STG IR of GHC.PrimopWrappers:<o:p></o:p></p>
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<span style="font-family:"Courier New"">extendInt8# [InlPrag=NOINLINE] :: Int8# -> Int#</span><br>
<span style="font-family:"Courier New"">[GblId, Arity=1, Unf=OtherCon []] =</span><br>
<span style="font-family:"Courier New""> \r [eta_B1] extendInt8# [eta_B1];</span><br>
<br>
<span style="font-family:"Courier New"">ord# [InlPrag=NOINLINE] :: Char# -> Int#</span><br>
<span style="font-family:"Courier New"">[GblId, Arity=1, Unf=OtherCon []] =</span><br>
<span style="font-family:"Courier New""> \r [eta_B1] ord# [eta_B1];</span><o:p></o:p></p>
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<o:p> </o:p></p>
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Where eta_B1 is redefined, so it is only unique in the scope.<o:p></o:p></p>
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Is this intentional?<o:p></o:p></p>
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<o:p> </o:p></p>
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Thanks,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Csaba Hruska<o:p></o:p></p>
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