Explain typeclass instance resolution

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He he, while I was poking about in the type inference code ...

There's an experimental command `:xplain` instance resolution.

The code to implement it needs switching on with a preprocessor flag set in
options.h.in then ./configure and recompile Hugs.

Use it by giving a constraint to be explained:

Hugs> :x Show (Maybe [Int])

(It seems a bit temperamental, fair enough for a hidden feature: if it
can't resolve an instance, it'll say so, but also give some misleading
messages with fragments of code leftover from previous uses.)


AntC

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<div dir=3D"auto">He he, while I was poking about in the type inference cod=
e ...</div><div dir=3D"auto"><br></div><div dir=3D"auto">There&#39;s an exp=
erimental command `:xplain` instance resolution.</div><div dir=3D"auto"><br=
></div><div dir=3D"auto">The code to implement it needs switching on with a=
 preprocessor flag set in <a href=3D"http://options.h.in">options.h.in</a> =
then ./configure and recompile Hugs.</div><div dir=3D"auto"><br></div><div =
dir=3D"auto">Use it by giving a constraint to be explained:</div><div dir=
=3D"auto"><br></div><div dir=3D"auto">Hugs&gt; :x Show (Maybe [Int])</div><=
div dir=3D"auto"><br></div><div dir=3D"auto">(It seems a bit temperamental,=
 fair enough for a hidden feature: if it can&#39;t resolve an instance, it&=
#39;ll say so, but also give some misleading messages with fragments of cod=
e leftover from previous uses.)</div><div dir=3D"auto"><br></div><div dir=
=3D"auto"><br></div><div dir=3D"auto">AntC</div>

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