[GHC] #8403: Pretty-printing of long types

[GHC]

#8403: Pretty-printing of long types
-------------------------------------+-------------------------------------
        Reporter:  monoidal          |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  lowest            |               Milestone:
       Component:  Compiler          |                 Version:  7.6.3
      Resolution:                    |                Keywords:  newcomer
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Other             |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:  #9428             |                Blocking:
                                     |  Differential Revisions:
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Comment (by phadej):

 With the test program:


 {{{
 import Text.PrettyPrint

 -- mocking how compiler/types/TypeRep.hs would print the type
 pairUntil :: Char -> Doc
 pairUntil c = pprArrowChain (varDocs ++ [resultPair])
   where varDocs = map char ['a'..c]
         resultPair = parens (sep (punctuate comma varDocs))

 arrow :: Doc
 arrow = text "->"

 pprArrowChain :: [Doc] -> Doc
 -- pprArrowChain [a,b,c]  generates   a -> b -> c
 pprArrowChain  []         = empty
 pprArrowChain (arg:args) = sep [arg, sep (map (arrow <+>) args)]
 }}}


 {{{
 λ> Test.pairUntil 'd'
 a -> b -> c -> d -> (a, b, c, d)
 λ> Test.pairUntil 'k'
 a
 -> b
 -> c
 -> d
 -> e
 -> f
 -> g
 -> h
 -> i
 -> j
 -> k
 -> (a, b, c, d, e, f, g, h, i, j, k)
 }}}

 I have no good ideas how to define "more packed", yet so output is still
 understandable. E.g. will this "less area" method work for all types:

 {{{
 a -> b -> c -> d -> e -> f -> g -> h -> i -> j
   -> k -> l -> m -> n -> o -> p -> q -> r -> s
   -> t -> u -> v -> w -> x
   -> (a, b, c, d, e, f, g, h, i, j, k, l,
       m, n, o, p, q, r, s, t, u, v, w, x)
 }}}

 My gut feelings that the layout algorithm won't be linear anymore, don't
 know if that is the problem though.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8403#comment:3>
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