Prettyprint Show output

Output of nested data structures by Show instances is often very hard to read. This package offers a simple function to insert line breaks and indentation into that output so that the semantics are unchanged, but makes it much easier to read.

The package does not rely on a parser for actual Haskell; instead, it merely reacts on parentheses, commas and the like. This makes it fairly robust even in the face of invalid Show instances, that may not produce valid Haskell code.

Examples

Artificial

Hello Foo ("(Bar", Haha) (Baz (A { foo = C, bar = D, qux = (E,"He)llo World!",G,
    H,[A,B,c,d,e,Fghi]) } ) (B,C) [Baz A1 B2, (Baz A3 (B4)), (Baz A5 (B6)), (Baz
    (A7) B8)]) (Foo) (Bar) (Baz (A) (B))

==>

Hello Foo ("(Bar",Haha)
          (Baz (A {foo = C
                  ,bar = D
                  ,qux = (E
                         ,"He)llo World!"
                         ,G
                         ,H
                         ,[A,B,c,d,e,Fghi])})
               (B,C)
               [Baz A1 B2
               ,(Baz A3 (B4))
               ,(Baz A5 (B6))
               ,(Baz (A7) B8)])
          (Foo)
          (Bar)
          (Baz (A) (B))

Inspired by a real AST

Set  (fromList [(Name "A string with (parenthesis",Ann  (Entry (Quality 1 1)
    (Ann  False) (Ann  (Map [Ann  (Bound (Ann  (Id "lorem"))),Ann  (Variable
    (Ann  (Id "ipsum")))])))),(Name "string",Ann  (Entry (Quality 1 1) (Ann
    True) (Ann  (Internal (Ann  (Reduce (Ann  (Id "dolor")) (Ann  (Id "sit")))))
    ))),(Name "Another } here",Ann  (Entry (Quality 1 1) (Ann  (Or [Ann  (Not
    (Ann  (Is (Ann  Flagged) (Ann  Type) (Ann  (Multi [Ann  (Literal (Ann  One))
    ]))))),Ann  (Is (Ann  Flagged) (Ann  Type) (Ann  (Multi [Ann  (Literal (Ann
    Three))]))),Ann  (Is (Ann  Flagged) (Ann  Type) (Ann  (Multi [Ann  (Literal
    (Ann  Two))])))])) (Ann  (Internal (Ann  (Concat (Ann  (Id "amet"))))))))])

==>

Set (fromList [(Name "A string with (parenthesis"
               ,Ann (Entry (Quality 1 1)
                           (Ann False)
                           (Ann (Map [Ann (Bound (Ann (Id "lorem")))
                                     ,Ann (Variable (Ann (Id "ipsum")))]))))
              ,(Name "string"
               ,Ann (Entry (Quality 1 1)
                           (Ann True)
                           (Ann (Internal (Ann (Reduce (Ann (Id "dolor"))
                                                       (Ann (Id "sit"))))))))
              ,(Name "Another } here"
               ,Ann (Entry (Quality 1 1)
                           (Ann (Or [Ann (Not (Ann (Is (Ann Flagged)
                                                       (Ann Type)
                                                       (Ann (Multi [Ann (Literal (Ann One))])))))
                                    ,Ann (Is (Ann Flagged)
                                             (Ann Type)
                                             (Ann (Multi [Ann (Literal (Ann Three))])))
                                    ,Ann (Is (Ann Flagged)
                                             (Ann Type)
                                             (Ann (Multi [Ann (Literal (Ann Two))])))]))
                           (Ann (Internal (Ann (Concat (Ann (Id "amet"))))))))])