[GHC] #10196: Regression regarding Unicode subscript characters in identifiers

[GHC]

#10196: Regression regarding Unicode subscript characters in identifiers
-------------------------------------+-------------------------------------
              Reporter:  thomie      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.10.2
             Component:  Compiler    |           Version:  7.10.1
  (Parser)                           |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  GHC rejects
          Architecture:              |  valid program
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:  #5108
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
 As reported by both hvr as user Yongqian Li:

 The Unicode7 update in GHC 7.10 had the side effect of breaking code
 making use of subscript symbols that did compile with GHC 7.8.4, but won't
 anymore with GHC 7.10.1:

 For instance, GHCi 7.8.4 accepts

    let xᵦ = 1
    let xᵤ = 1
    let xᵩ = 1
    let xᵢ = 1
    let xᵪ = 1
    let xᵣ = 1
    let xₙ = 1

 whereas GHC 7.10.1RC fails parsing those with a lexical error. (NB: GHC
 7.8 does not accept *all* latin subscript letters either).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10196>
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