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can't infer type args for scalaz.Leibniz.symm ? #8655

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scabug opened this issue Jun 10, 2014 · 6 comments
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can't infer type args for scalaz.Leibniz.symm ? #8655

scabug opened this issue Jun 10, 2014 · 6 comments
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@scabug
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scabug commented Jun 10, 2014

code at http://scastie.org/5684

In a call to:

{code}Leibniz.symm(G.leibniz){code} where {code}G.A = A0{code}

I get this inference failure:

[error]  found   : scalaz.Leibniz.===[FA,G.M[G.A]]
[error]     (which expands to)  scalaz.Leibniz[Nothing,Any,FA,G.M[G.A]]
[error]  required: scalaz.Leibniz[L,Any,FA,G.M[G.A]]
[error]     Leibniz.symm(G.leibniz)
[error]                    ^

which seems silly. L should be inferred as Nothing in this case.

{code}Leibniz.symmNothing,Any,FA,G.M[G.A]{code}

compiles fine, but is unnecessarily ugly.

@scabug
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scabug commented Jun 10, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8655?orig=1
Reporter: @refried
Affected Versions: 2.10.2, 2.10.3, 2.11.1
Attachments:

@scabug
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scabug commented Jun 11, 2014

@retronym said:
Could you please prune the test case down to something standalone (ie, move the involved implicits and data types into the test case)?

@scabug
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scabug commented Jun 11, 2014

@retronym said:
I suspect that the limitation will be the same as the one discussed here: https://groups.google.com/d/msg/scala-internals/s1MFKtpN_Kc/AVYCgB6WGL0J

@scabug
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scabug commented Jun 11, 2014

@refried said:
attached file.

@scabug scabug added the backend label Apr 7, 2017
@SethTisue
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needs minimization.

@joroKr21
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duplicates #1570 and #9453

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