[GHC] #15601: Unexpected compile error on type level lists with a single element

[GHC]

#15601: Unexpected compile error on type level lists with a single element
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        Reporter:  erikd             |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by monoidal):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 This is unfortunately by design.

 When type-level lists were added, the syntax `[a]` was already taken. For
 example `[Integer]` is a list of integers, kind `*`. It's not a type-level
 list with one entry, which would be kind `[*]`.

 If we could start Haskell from scratch I would vote for having `['a', 'b']
 :: List Char` instead of `['a', 'b'] :: [Char]` but it's too late to
 change.

 See
 https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html
 #promoted-list-and-tuple-types

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15601#comment:1>
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