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<p class="MsoNormal"><span lang="EN-US">Dear GHC-ers,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Is there a reason for explicitly broken Data.Data instances? Case in point:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> instance Data Var where<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> -- don't traverse?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> toConstr _ = abstractConstr "Var"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> gunfold _ _ = error "gunfold"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> dataTypeOf _ = mkNoRepType "Var"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I understand (vaguely) arguments about abstract data types, but this also excludes convenient queries that can, e.g. extract all types from a CoreExpr. I had hoped to do stuff like this:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> collect :: (Typeable b, Data a, MonadPlus m) => a -> m b<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> collect = everything mplus $ mkQ mzero return<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> allTypes :: CoreExpr -> [Type]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> allTypes = collect<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Especially when still exploring (parts of) the GHC API, being able to extract things in this fashion is very helpful. SYB’s “everything” being broken by these instances, not so much.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Would a patch “fixing” these instances be acceptable?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Philip<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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