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<p class="MsoNormal">Thomas<o:p></o:p></p>
<p class="MsoNormal">I was looking at <a href="http://ghc.haskell.org/trac/ghc/ticket/10045">
Trac #10045</a>. I know exactly what is going on, but my investigation triggered several questions.<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>What is the state of the ToDos on <a href="https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures">
https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures</a>?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Is a named wildcard supposed to have any scope? For example:<o:p></o:p></p>
<p class="Code">f :: _a -> b -> _a<o:p></o:p></p>
<p class="Code">f x y = x :: _a<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt">The _a in the signature is not supposed to have any lexical scope over the binding is it? That would be entirely inconsistent with the treatment of ordinary type variables (such as ‘b’ in the example) which only
scope if you have an explicit ‘forall b’.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt">Assuming the answer is “no” (and I really think it should be no), what is the call to tcExtendTyVarEnv2 tvsAndNcs doing in TcBinds.tcRhs? I’m pretty certain it bring into scope only the sig_tvs, and NOT the sig_nwcs.<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>If that is true, I think we may not need the sig_nwcs field of TcSigInfo at all.<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>A TcSigInfo has a sig_id field, which is intended to give the fixed, fully-known polymorphic type of the function. This is used:<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>for polymorphic recursion<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>as the type of the function to use in the body of the let, even if typechecking the function itself fails.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt">Neither of these makes sense for partial type sigs. (And in fact, using sig_id for a partial type sig is what gives rise to #10045.) So I’m pretty convinced that we should replace sig_id and sig_partial with
a single field sig_id :: Maybe Id, which is Nothing for partial sigs, and (Just ty) for total sigs.<o:p></o:p></p>
<p class="MsoNormal">I wanted to check with you before blundering in and doing this. Or you could.<o:p></o:p></p>
<p class="MsoNormal">RSVP<o:p></o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal">Simon<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
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