[GHC] #14341: Show instance for TypeReps is a bit broken

[GHC]

#14341: Show instance for TypeReps is a bit broken
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.2.1
      Resolution:                    |             Keywords:  Typeable
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4084
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by dfeuer:

Old description:

> There are two problems.
>
> 1. Showing typereps of tuples can produce unnecessary parentheses:
>
> {{{
> Prelude K T> typeRep @(Int, Maybe Bool)
> (Int,(Maybe Bool))
> }}}
>
>    The fix is trivial.
>
> 2. Showing typereps of ticked (i.e., lifted) tuples and lists gives hard-
> to-read results, because it does not use the usual special syntax:
>
> {{{
> Prelude K T> typeRep @'(Int, Maybe Bool)
> '(,) * * Int (Maybe Bool)
>
> Prelude K T> typeRep @'[1,2,3]
> ': Nat 1 (': Nat 2 (': Nat 3 ('[] Nat)))
> }}}
>
>    Fixing the lifted tuple case is trivial. Fixing the lifted list case
> is slightly less trivial, but not hard.

New description:

 There are three problems.

 1. Showing typereps of tuples can produce unnecessary parentheses:

 {{{
 Prelude K T> typeRep @(Int, Maybe Bool)
 (Int,(Maybe Bool))
 }}}

    The fix is trivial.

 2. Showing typereps of ticked (i.e., lifted) tuples and lists gives hard-
 to-read results, because it does not use the usual special syntax:

 {{{
 Prelude K T> typeRep @'(Int, Maybe Bool)
 '(,) * * Int (Maybe Bool)

 Prelude K T> typeRep @'[1,2,3]
 ': Nat 1 (': Nat 2 (': Nat 3 ('[] Nat)))
 }}}

    Fixing the lifted tuple case is trivial. Fixing the lifted list case is
 slightly less trivial, but not hard.

 3. Type operator applications are not shown infix.

 {{{
 Prelude K T> typeRep @(Maybe :*: Either Int)
 :*: * Maybe (Either Int)
 }}}

 This is the hardest problem to fix, although it's probably not too
 terribly hard. See comment:1 for thoughts.

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14341#comment:2>
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