[GHC] #8705: Type inference regression with local dictionaries

[GHC]

#8705: Type inference regression with local dictionaries
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        Reporter:  goldfire                 |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  high                     |        Milestone:  7.8.1
       Component:  Compiler (Type checker)  |          Version:  7.8.1-rc1
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by simonpj):

 Just to check, we have three givens:
 {{{
 G1:   lst ~ n1 : []
 G2:   lst ~ n0 : n2
 G3:   n :<=: n2
 }}}
 From the G1,G2 we find `n1 ~ n0`, and from that and G3 we get `n :<=: n1`,
 which is what we want to prove.

 Is that the reasoning?

 Would it be difficult to drop the dependence on `singletons`, or include
 the code from there that's needed directly into this module?

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8705#comment:3>
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