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  • Richard Eisenberg's avatar
    Slightly better `Coercible` errors. · 2f9809ef
    Richard Eisenberg authored
    This makes two real changes:
     - Equalities like (a ~R [a]) really *are* insoluble. Previously,
       GHC refused to give up when an occurs check bit on a representational
       equality. But for datatypes, it really should bail.
    
     - Now, GHC will sometimes report an occurs check error (in cases above)
       for representational equalities. Previously, it never did.
    
    This "fixes" #10715, where by "fix", I mean clarifies the error message.
    It's unclear how to do more to fix that ticket.
    
    Test cases: typecheck/should_fail/T10715{,b}
    2f9809ef