wl-pprint-extras-3.5.0.5: A free monad based on the Wadler/Leijen pretty printer

Copyright | Google, Inc. (c) 2013, Edward Kmett (c) 2011, Daan Leijen (c) 2000
License | BSD-style (see the file LICENSE)
Maintainer | ekmett@gmail.com
Stability | experimental
Portability | portable
Safe Haskell | Safe
Language | Haskell98

Text.PrettyPrint.Free.Internal

Contents

- Documents
- Basic combinators
- Alignment
- Operators
- List combinators
- Fillers
- Bracketing combinators
- Character documents
- Pretty class
- Rendering
- Undocumented
- Re-exported standard functions

Description

Pretty print module based on Daan Leijen's implementation of Philip Wadler's "prettier printer"

         "A prettier printer"
         Draft paper, April 1997, revised March 1998.
         http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf

This is an implementation of the pretty printing combinators described by Philip Wadler (1997). In their bare essence, the combinators of Wadler are not expressive enough to describe some commonly occurring layouts. The PPrint library adds new primitives to describe these layouts and works well in practice.

The library is based on a single way to concatenate documents, which is associative and has both a left and right unit. This simple design leads to an efficient and short implementation. The simplicity is reflected in the predictable behaviour of the combinators which make them easy to use in practice.

A thorough description of the primitive combinators and their implementation can be found in Philip Wadler's paper (1997). Additions and the main differences with his original paper are:

- The nil document is called empty.
- The operator `</>` is used for soft line breaks.
- There are three new primitives: `align`, `fill` and `fillBreak`. These are very useful in practice.
- Lots of other useful combinators, like `fillSep` and `list`.
- There are two renderers, `renderPretty` for pretty printing and `renderCompact` for compact output. The pretty printing algorithm also uses a ribbon-width now for even prettier output.
- There are two display routines, `displayS` for strings and `displayIO` for file based output.
- There is a `Pretty` class.
- The implementation uses optimised representations and strictness annotations.
- A type argument has been added and embedded `effects` can be seen in the SimpleDoc type.

Synopsis

- data Doc e
  - = Fail
  - | Empty
  - | Char !Char
  - | Text !Int String
  - | Line
  - | FlatAlt (Doc e) (Doc e)
  - | Cat (Doc e) (Doc e)
  - | Nest !Int (Doc e)
  - | Union (Doc e) (Doc e)
  - | Effect e
  - | Column (Int -> Doc e)
  - | Nesting (Int -> Doc e)
  - | Columns (Int -> Doc e)
  - | Ribbon (Int -> Doc e)
- putDoc :: Doc e -> IO ()
- hPutDoc :: Handle -> Doc e -> IO ()
- char :: Char -> Doc e
- text :: String -> Doc e
- nest :: Int -> Doc e -> Doc e
- line :: Doc e
- linebreak :: Doc e
- group :: Doc e -> Doc e
- softline :: Doc e
- softbreak :: Doc e
- hardline :: Doc e
- flatAlt :: Doc e -> Doc e -> Doc e
- flatten :: Doc e -> Doc e
- align :: Doc e -> Doc e
- hang :: Int -> Doc e -> Doc e
- indent :: Int -> Doc e -> Doc e
- encloseSep :: Foldable f => Doc e -> Doc e -> Doc e -> f (Doc e) -> Doc e
- list :: Foldable f => f (Doc e) -> Doc e
- tupled :: Foldable f => f (Doc e) -> Doc e
- semiBraces :: Foldable f => f (Doc e) -> Doc e
- (<+>) :: Doc e -> Doc e -> Doc e
- above :: Doc e -> Doc e -> Doc e
- (</>) :: Doc e -> Doc e -> Doc e
- aboveBreak :: Doc e -> Doc e -> Doc e
- (<//>) :: Doc e -> Doc e -> Doc e
- hsep :: Foldable f => f (Doc e) -> Doc e
- vsep :: Foldable f => f (Doc e) -> Doc e
- fillSep :: Foldable f => f (Doc e) -> Doc e
- sep :: Foldable f => f (Doc e) -> Doc e
- hcat :: Foldable f => f (Doc e) -> Doc e
- vcat :: Foldable f => f (Doc e) -> Doc e
- fillCat :: Foldable f => f (Doc e) -> Doc e
- cat :: Foldable f => f (Doc e) -> Doc e
- punctuate :: Traversable f => Doc e -> f (Doc e) -> f (Doc e)
- fill :: Int -> Doc e -> Doc e
- fillBreak :: Int -> Doc e -> Doc e
- enclose :: Doc e -> Doc e -> Doc e -> Doc e
- squotes :: Doc e -> Doc e
- dquotes :: Doc e -> Doc e
- parens :: Doc e -> Doc e
- angles :: Doc e -> Doc e
- braces :: Doc e -> Doc e
- brackets :: Doc e -> Doc e
- lparen :: Doc e
- rparen :: Doc e
- langle :: Doc e
- rangle :: Doc e
- lbrace :: Doc e
- rbrace :: Doc e
- lbracket :: Doc e
- rbracket :: Doc e
- squote :: Doc e
- dquote :: Doc e
- semi :: Doc e
- colon :: Doc e
- comma :: Doc e
- space :: Doc e
- dot :: Doc e
- backslash :: Doc e
- equals :: Doc e
- class Pretty a where
- data SimpleDoc e
  - = SFail
  - | SEmpty
  - | SChar !Char (SimpleDoc e)
  - | SText !Int String (SimpleDoc e)
  - | SLine !Int (SimpleDoc e)
  - | SEffect e (SimpleDoc e)
- renderPretty :: Float -> Int -> Doc e -> SimpleDoc e
- renderCompact :: Doc e -> SimpleDoc e
- renderSmart :: Int -> Doc e -> SimpleDoc e
- displayS :: SimpleDoc e -> ShowS
- displayIO :: Handle -> SimpleDoc e -> IO ()
- column :: (Int -> Doc e) -> Doc e
- nesting :: (Int -> Doc e) -> Doc e
- width :: Doc e -> (Int -> Doc e) -> Doc e
- columns :: (Int -> Doc e) -> Doc e
- ribbon :: (Int -> Doc e) -> Doc e
- empty :: Alternative f => forall a. f a
- (<>) :: Semigroup a => a -> a -> a

# Documents

data Doc e #

The abstract data type `Doc` represents pretty documents.

`Doc` is an instance of the `Show` class. `(show doc)` pretty prints document `doc` with a page width of 100 characters and a ribbon width of 40 characters.

    show (text "hello" `above` text "world")

Which would return the string "hello\nworld", i.e.

    hello
    world

Constructors

Fail |
Empty |
Char !Char |
Text !Int String |
Line |
FlatAlt (Doc e) (Doc e) |
Cat (Doc e) (Doc e) |
Nest !Int (Doc e) |
Union (Doc e) (Doc e) |
Effect e |
Column (Int -> Doc e) |
Nesting (Int -> Doc e) |
Columns (Int -> Doc e) |
Ribbon (Int -> Doc e) |

Instances

Monad Doc # |
Methods (>>=) :: Doc a -> (a -> Doc b) -> Doc b # (>>) :: Doc a -> Doc b -> Doc b # return :: a -> Doc a # fail :: String -> Doc a #
Functor Doc # |
Methods fmap :: (a -> b) -> Doc a -> Doc b # (<$) :: a -> Doc b -> Doc a #
Applicative Doc # |
Methods pure :: a -> Doc a # (<*>) :: Doc (a -> b) -> Doc a -> Doc b # (*>) :: Doc a -> Doc b -> Doc b # (<*) :: Doc a -> Doc b -> Doc a #
Alternative Doc # |
Methods empty :: Doc a # (<|>) :: Doc a -> Doc a -> Doc a # some :: Doc a -> Doc [a] # many :: Doc a -> Doc [a] #
MonadPlus Doc # |
Methods mzero :: Doc a # mplus :: Doc a -> Doc a -> Doc a #
Plus Doc # |
Methods zero :: Doc a #
Alt Doc # |
Methods (<!>) :: Doc a -> Doc a -> Doc a # some :: Applicative Doc => Doc a -> Doc [a] # many :: Applicative Doc => Doc a -> Doc [a] #
Apply Doc # |
Methods (<.>) :: Doc (a -> b) -> Doc a -> Doc b # (.>) :: Doc a -> Doc b -> Doc b # (<.) :: Doc a -> Doc b -> Doc a #
Bind Doc # |
Methods (>>-) :: Doc a -> (a -> Doc b) -> Doc b # join :: Doc (Doc a) -> Doc a #
Show (Doc e) # |
Methods showsPrec :: Int -> Doc e -> ShowS # show :: Doc e -> String # showList :: [Doc e] -> ShowS #
IsString (Doc e) # |
Methods fromString :: String -> Doc e #
Semigroup (Doc e) # |
Methods (<>) :: Doc e -> Doc e -> Doc e # sconcat :: NonEmpty (Doc e) -> Doc e # stimes :: Integral b => b -> Doc e -> Doc e #
Monoid (Doc e) # |
Methods mempty :: Doc e # mappend :: Doc e -> Doc e -> Doc e # mconcat :: [Doc e] -> Doc e #
Pretty (Doc a) # |
Methods pretty :: Doc a -> Doc e # prettyList :: [Doc a] -> Doc e #

putDoc :: Doc e -> IO () #

The action `(putDoc doc)` pretty prints document `doc` to the standard output, with a page width of 100 characters and a ribbon width of 40 characters.

    main :: IO ()
    main = do{ putDoc (text "hello" <+> text "world") }

Which would output

    hello world

hPutDoc :: Handle -> Doc e -> IO () #

`(hPutDoc handle doc)` pretty prints document `doc` to the file handle `handle` with a page width of 100 characters and a ribbon width of 40 characters.

    main = do{ handle <- openFile "MyFile" WriteMode
             ; hPutDoc handle (vcat (map text
                               ["vertical","text"]))
             ; hClose handle
             }

# Basic combinators

char :: Char -> Doc e #

The document `(char c)` contains the literal character `c`. The character shouldn't be a newline (`'\n'`), the function `line` should be used for line breaks.

text :: String -> Doc e #

The document `(text s)` contains the literal string `s`. The string shouldn't contain any newline (`'\n'`) characters. If the string contains newline characters, the function `string` should be used.

nest :: Int -> Doc e -> Doc e #

The document `(nest i x)` renders document `x` with the current indentation level increased by i (See also `hang`, `align` and `indent`).

    nest 2 (text "hello" `above` text "world") `above` text "!"

outputs as:

    hello
      world
    !

line :: Doc e #

The `line` document advances to the next line and indents to the current nesting level. Document `line` behaves like `(text " ")` if the line break is undone by `group`.

linebreak :: Doc e #

The `linebreak` document advances to the next line and indents to the current nesting level. Document `linebreak` behaves like `empty` if the line break is undone by `group`.

group :: Doc e -> Doc e #

The `group` combinator is used to specify alternative layouts. The document `(group x)` undoes all line breaks in document `x`. The resulting line is added to the current line if that fits the page. Otherwise, the document `x` is rendered without any changes.

softline :: Doc e #

The document `softline` behaves like `space` if the resulting output fits the page, otherwise it behaves like `line`.

    softline = group line

softbreak :: Doc e #

The document `softbreak` behaves like `empty` if the resulting output fits the page, otherwise it behaves like `line`.

    softbreak  = group linebreak

hardline :: Doc e #

A linebreak that can not be flattened; it is guaranteed to be rendered as a newline.

flatAlt :: Doc e -> Doc e -> Doc e #

`flatAlt` creates a document that changes when flattened; normally it is rendered as the first argument, but when flattened is rendered as the second.

flatten :: Doc e -> Doc e #

# Alignment

align :: Doc e -> Doc e #

The document `(align x)` renders document `x` with the nesting level set to the current column. It is used for example to implement `hang`.

As an example, we will put a document right above another one, regardless of the current nesting level:

    x $$ y  = align (above x y)

    test    = text "hi" <+> (text "nice" $$ text "world")

which will be layed out as:

    hi nice
       world

hang :: Int -> Doc e -> Doc e #

The hang combinator implements hanging indentation. The document `(hang i x)` renders document `x` with a nesting level set to the current column plus `i`. The following example uses hanging indentation for some text:

    test  = hang 4 (fillSep (map text
            (words "the hang combinator indents these words !")))

Which lays out on a page with a width of 20 characters as:

    the hang combinator
        indents these
        words !

The `hang` combinator is implemented as:

    hang i x  = align (nest i x)

indent :: Int -> Doc e -> Doc e #

The document `(indent i x)` indents document `x` with `i` spaces.

    test  = indent 4 (fillSep (map text
            (words "the indent combinator indents these words !")))

Which lays out with a page width of 20 as:

        the indent
        combinator
        indents these
        words !

encloseSep :: Foldable f => Doc e -> Doc e -> Doc e -> f (Doc e) -> Doc e #

The document `(encloseSep l r sep xs)` concatenates the documents `xs` separated by `sep` and encloses the resulting document by `l` and `r`. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All separators are put in front of the elements. For example, the combinator `list` can be defined with `encloseSep`:

    list xs = encloseSep lbracket rbracket comma xs
    test    = text "list" <+> (list (map int [10,200,3000]))

Which is layed out with a page width of 20 as:

    list [10, 200, 3000]

But when the page width is 15, it is layed out as:

    list [ 10
         , 200
         , 3000 ]

list :: Foldable f => f (Doc e) -> Doc e #

The document `(list xs)` comma separates the documents `xs` and encloses them in square brackets. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All comma separators are put in front of the elements.

tupled :: Foldable f => f (Doc e) -> Doc e #

The document `(tupled xs)` comma separates the documents `xs` and encloses them in parenthesis. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All comma separators are put in front of the elements.

semiBraces :: Foldable f => f (Doc e) -> Doc e #

The document `(semiBraces xs)` separates the documents `xs` with semi colons and encloses them in braces. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All semi colons are put in front of the elements.

# Operators

(<+>) :: Doc e -> Doc e -> Doc e infixr 6 #

above :: Doc e -> Doc e -> Doc e infixr 5 #

The document `above x y` concatenates document `x` and `y` with a `line` in between. (infixr 5)

(</>) :: Doc e -> Doc e -> Doc e infixr 5 #

The document `(x </> y)` concatenates document `x` and `y` with a `softline` in between. This effectively puts `x` and `y` either next to each other (with a `space` in between) or underneath each other. (infixr 5)

aboveBreak :: Doc e -> Doc e -> Doc e infixr 5 #

The document `aboveBreak x y` concatenates document `x` and `y` with a `linebreak` in between. (infixr 5)

(<//>) :: Doc e -> Doc e -> Doc e infixr 5 #

The document `(x <//> y)` concatenates document `x` and `y` with a `softbreak` in between. This effectively puts `x` and `y` either right next to each other or underneath each other. (infixr 5)

# List combinators

hsep :: Foldable f => f (Doc e) -> Doc e #

The document `(hsep xs)` concatenates all documents `xs` horizontally with `(<+>)`.

vsep :: Foldable f => f (Doc e) -> Doc e #

The document `(vsep xs)` concatenates all documents `xs` vertically with `above`. If a `group` undoes the line breaks inserted by `vsep`, all documents are separated with a space.

    someText = map text (words ("text to lay out"))

    test     = text "some" <+> vsep someText

This is layed out as:

    some text
    to
    lay
    out

The `align` combinator can be used to align the documents under their first element

    test = text "some" <+> align (vsep someText)

Which is printed as:

    some text
         to
         lay
         out

fillSep :: Foldable f => f (Doc e) -> Doc e #

The document `(fillSep xs)` concatenates documents `xs` horizontally with `(<+>)` as long as its fits the page, then inserts a `line` and continues doing that for all documents in `xs`.

    fillSep xs  = foldr (</>) empty xs

sep :: Foldable f => f (Doc e) -> Doc e #

The document `(sep xs)` concatenates all documents `xs` either horizontally with `(<+>)`, if it fits the page, or vertically with `above`.

    sep xs  = group (vsep xs)

hcat :: Foldable f => f (Doc e) -> Doc e #

The document `(hcat xs)` concatenates all documents `xs` horizontally with `(<>)`.

vcat :: Foldable f => f (Doc e) -> Doc e #

The document `(vcat xs)` concatenates all documents `xs` vertically with `aboveBreak`. If a `group` undoes the line breaks inserted by `vcat`, all documents are directly concatenated.

fillCat :: Foldable f => f (Doc e) -> Doc e #

The document `(fillCat xs)` concatenates documents `xs` horizontally with `(<>)` as long as its fits the page, then inserts a `linebreak` and continues doing that for all documents in `xs`.

    fillCat xs  = foldr (<//>) empty xs

cat :: Foldable f => f (Doc e) -> Doc e #

The document `(cat xs)` concatenates all documents `xs` either horizontally with `(<>)`, if it fits the page, or vertically with `aboveBreak`.

    cat xs  = group (vcat xs)

punctuate :: Traversable f => Doc e -> f (Doc e) -> f (Doc e) #

`(punctuate p xs)` concatenates all documents in `xs` with document `p` except for the last document.

    someText = map text ["words","in","a","tuple"]
    test     = parens (align (cat (punctuate comma someText)))

This is layed out on a page width of 20 as:

    (words,in,a,tuple)

But when the page width is 15, it is layed out as:

    (words,
     in,
     a,
     tuple)

(If you want put the commas in front of their elements instead of at the end, you should use `tupled` or, in general, `encloseSep`.)

# Fillers

fill :: Int -> Doc e -> Doc e #

The document `(fill i x)` renders document `x`. It then appends `space`s until the width is equal to `i`. If the width of `x` is already larger, nothing is appended. This combinator is quite useful in practice to output a list of bindings. The following example demonstrates this.

    types  = [("empty","Doc e")
             ,("nest","Int -> Doc e -> Doc e")
             ,("linebreak","Doc e")]

    ptype (name,tp)
           = fill 6 (text name) <+> text "::" <+> text tp

    test   = text "let" <+> align (vcat (map ptype types))

Which is layed out as:

    let empty  :: Doc e
        nest   :: Int -> Doc e -> Doc e
        linebreak :: Doc e

fillBreak :: Int -> Doc e -> Doc e #

The document `(fillBreak i x)` first renders document `x`. It then appends `space`s until the width is equal to `i`. If the width of `x` is already larger than `i`, the nesting level is increased by `i` and a `line` is appended. When we redefine `ptype` in the previous example to use `fillBreak`, we get a useful variation of the previous output:

    ptype (name,tp)
           = fillBreak 6 (text name) <+> text "::" <+> text tp

The output will now be:

    let empty  :: Doc e
        nest   :: Int -> Doc e -> Doc e
        linebreak
               :: Doc e

# Bracketing combinators

enclose :: Doc e -> Doc e -> Doc e -> Doc e #

The document `(enclose l r x)` encloses document `x` between documents `l` and `r` using `(<>)`.

    enclose l r x   = l <> x <> r

squotes :: Doc e -> Doc e #

Document `(squotes x)` encloses document `x` with single quotes "'".

dquotes :: Doc e -> Doc e #

Document `(dquotes x)` encloses document `x` with double quotes '"'.

parens :: Doc e -> Doc e #

Document `(parens x)` encloses document `x` in parenthesis, "(" and ")".

angles :: Doc e -> Doc e #

Document `(angles x)` encloses document `x` in angles, "<" and ">".

braces :: Doc e -> Doc e #

Document `(braces x)` encloses document `x` in braces, "{" and "}".

brackets :: Doc e -> Doc e #

Document `(brackets x)` encloses document `x` in square brackets, "[" and "]".

# Character documents

lparen :: Doc e #

The document `lparen` contains a left parenthesis, "(".

rparen :: Doc e #

The document `rparen` contains a right parenthesis, ")".

langle :: Doc e #

The document `langle` contains a left angle, "<".

rangle :: Doc e #

The document `rangle` contains a right angle, ">".

lbrace :: Doc e #

The document `lbrace` contains a left brace, "{".

rbrace :: Doc e #

The document `rbrace` contains a right brace, "}".

lbracket :: Doc e #

The document `lbracket` contains a left square bracket, "[".

rbracket :: Doc e #

The document `rbracket` contains a right square bracket, "]".

squote :: Doc e #

The document `squote` contains a single quote, "'".

dquote :: Doc e #

The document `dquote` contains a double quote, '"'.

semi :: Doc e #

The document `semi` contains a semi colon, ";".

colon :: Doc e #

The document `colon` contains a colon, ":".

comma :: Doc e #

The document `comma` contains a comma, ",".

space :: Doc e #

The document `space` contains a single space, " ".

    x <+> y   = x <> space <> y

dot :: Doc e #

The document `dot` contains a single dot, ".".

backslash :: Doc e #

The document `backslash` contains a back slash, "\".

equals :: Doc e #

The document `equals` contains an equal sign, "=".

# Pretty class

class Pretty a where #

The member `prettyList` is only used to define the `instance Pretty a => Pretty [a]`. In normal circumstances only the `pretty` function is used.

Minimal complete definition

pretty

Methods

pretty :: a -> Doc e #

prettyList :: [a] -> Doc e #

Instances

Pretty Bool # |
Methods pretty :: Bool -> Doc e # prettyList :: [Bool] -> Doc e #
Pretty Char # |
Methods pretty :: Char -> Doc e # prettyList :: [Char] -> Doc e #
Pretty Double # |
Methods pretty :: Double -> Doc e # prettyList :: [Double] -> Doc e #
Pretty Float # |
Methods pretty :: Float -> Doc e # prettyList :: [Float] -> Doc e #
Pretty Int # |
Methods pretty :: Int -> Doc e # prettyList :: [Int] -> Doc e #
Pretty Int8 # |
Methods pretty :: Int8 -> Doc e # prettyList :: [Int8] -> Doc e #
Pretty Int16 # |
Methods pretty :: Int16 -> Doc e # prettyList :: [Int16] -> Doc e #
Pretty Int32 # |
Methods pretty :: Int32 -> Doc e # prettyList :: [Int32] -> Doc e #
Pretty Int64 # |
Methods pretty :: Int64 -> Doc e # prettyList :: [Int64] -> Doc e #
Pretty Integer # |
Methods pretty :: Integer -> Doc e # prettyList :: [Integer] -> Doc e #
Pretty Word # |
Methods pretty :: Word -> Doc e # prettyList :: [Word] -> Doc e #
Pretty Word8 # |
Methods pretty :: Word8 -> Doc e # prettyList :: [Word8] -> Doc e #
Pretty Word16 # |
Methods pretty :: Word16 -> Doc e # prettyList :: [Word16] -> Doc e #
Pretty Word32 # |
Methods pretty :: Word32 -> Doc e # prettyList :: [Word32] -> Doc e #
Pretty Word64 # |
Methods pretty :: Word64 -> Doc e # prettyList :: [Word64] -> Doc e #
Pretty () # |
Methods pretty :: () -> Doc e # prettyList :: [()] -> Doc e #
Pretty Natural # |
Methods pretty :: Natural -> Doc e # prettyList :: [Natural] -> Doc e #
Pretty ByteString # |
Methods pretty :: ByteString -> Doc e # prettyList :: [ByteString] -> Doc e #
Pretty ByteString # |
Methods pretty :: ByteString -> Doc e # prettyList :: [ByteString] -> Doc e #
Pretty Text # |
Methods pretty :: Text -> Doc e # prettyList :: [Text] -> Doc e #
Pretty Text # |
Methods pretty :: Text -> Doc e # prettyList :: [Text] -> Doc e #
Pretty a => Pretty [a] # |
Methods pretty :: [a] -> Doc e # prettyList :: [[a]] -> Doc e #
Pretty a => Pretty (Maybe a) # |
Methods pretty :: Maybe a -> Doc e # prettyList :: [Maybe a] -> Doc e #
Pretty a => Pretty (NonEmpty a) # |
Methods pretty :: NonEmpty a -> Doc e # prettyList :: [NonEmpty a] -> Doc e #
Pretty a => Pretty (Seq a) # |
Methods pretty :: Seq a -> Doc e # prettyList :: [Seq a] -> Doc e #
Pretty (Doc a) # |
Methods pretty :: Doc a -> Doc e # prettyList :: [Doc a] -> Doc e #
(Pretty a, Pretty b) => Pretty (a, b) # |
Methods pretty :: (a, b) -> Doc e # prettyList :: [(a, b)] -> Doc e #
(Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) # |
Methods pretty :: (a, b, c) -> Doc e # prettyList :: [(a, b, c)] -> Doc e #

# Rendering

data SimpleDoc e #

The data type `SimpleDoc` represents rendered documents and is used by the display functions.

The `Int` in `SText` contains the length of the string. The `Int` in `SLine` contains the indentation for that line. The library provides two default display functions `displayS` and `displayIO`. You can provide your own display function by writing a function from a `SimpleDoc` to your own output format.

Constructors

SFail |
SEmpty |
SChar !Char (SimpleDoc e) |
SText !Int String (SimpleDoc e) |
SLine !Int (SimpleDoc e) |
SEffect e (SimpleDoc e) |

Instances

Functor SimpleDoc # |
Methods fmap :: (a -> b) -> SimpleDoc a -> SimpleDoc b # (<$) :: a -> SimpleDoc b -> SimpleDoc a #
Foldable SimpleDoc # |
Methods fold :: Monoid m => SimpleDoc m -> m # foldMap :: Monoid m => (a -> m) -> SimpleDoc a -> m # foldr :: (a -> b -> b) -> b -> SimpleDoc a -> b # foldr' :: (a -> b -> b) -> b -> SimpleDoc a -> b # foldl :: (b -> a -> b) -> b -> SimpleDoc a -> b # foldl' :: (b -> a -> b) -> b -> SimpleDoc a -> b # foldr1 :: (a -> a -> a) -> SimpleDoc a -> a # foldl1 :: (a -> a -> a) -> SimpleDoc a -> a # toList :: SimpleDoc a -> [a] # null :: SimpleDoc a -> Bool # length :: SimpleDoc a -> Int # elem :: Eq a => a -> SimpleDoc a -> Bool # maximum :: Ord a => SimpleDoc a -> a # minimum :: Ord a => SimpleDoc a -> a # sum :: Num a => SimpleDoc a -> a # product :: Num a => SimpleDoc a -> a #
Traversable SimpleDoc # |
Methods traverse :: Applicative f => (a -> f b) -> SimpleDoc a -> f (SimpleDoc b) # sequenceA :: Applicative f => SimpleDoc (f a) -> f (SimpleDoc a) # mapM :: Monad m => (a -> m b) -> SimpleDoc a -> m (SimpleDoc b) # sequence :: Monad m => SimpleDoc (m a) -> m (SimpleDoc a) #

renderPretty :: Float -> Int -> Doc e -> SimpleDoc e #

This is the default pretty printer which is used by `show`, `putDoc` and `hPutDoc`. `(renderPretty ribbonfrac width x)` renders document `x` with a page width of `width` and a ribbon width of `(ribbonfrac * width)` characters. The ribbon width is the maximal amount of non-indentation characters on a line. The parameter `ribbonfrac` should be between `0.0` and `1.0`. If it is lower or higher, the ribbon width will be 0 or `width` respectively.

renderCompact :: Doc e -> SimpleDoc e #

`(renderCompact x)` renders document `x` without adding any indentation. Since no 'pretty' printing is involved, this renderer is very fast. The resulting output contains fewer characters than a pretty printed version and can be used for output that is read by other programs.

renderSmart :: Int -> Doc e -> SimpleDoc e #

A slightly smarter rendering algorithm with more lookahead. It provides provide earlier breaking on deeply nested structures. For example, consider this python-ish pseudocode: `fun(fun(fun(fun(fun([abcdefg, abcdefg])))))` If we put a softbreak (+ nesting 2) after each open parenthesis, and align the elements of the list to match the opening brackets, this will render with `renderPretty` and a page width of 20c as: `fun(fun(fun(fun(fun([ | abcdef, | abcdef, ] ))))) |` Where the 20c. boundary has been marked with |. Because `renderPretty` only uses one-line lookahead, it sees that the first line fits, and is stuck putting the second and third lines after the 20c mark. In contrast, `renderSmart` will continue to check the potential document up to the end of the indentation level. Thus, it will format the document as:

    fun(                |
      fun(              |
        fun(            |
          fun(          |
            fun([       |
                  abcdef,
                  abcdef,
                ]       |
      )))))             |

Which fits within the 20c. mark. In addition, `renderSmart` uses this lookahead to minimize the number of lines printed, leading to more compact and visually appealing output. Consider this example using the same syntax as above: `aaaaaaaaaaa([abc, def, ghi])` When rendered with `renderPretty` and a page width of 20c, we get: `aaaaaaaaaaa([ abc , def , ghi ])` Whereas when rendered with `renderSmart` and a page width of 20c, we get: `aaaaaaaaaaa( [abc, def, ghi])`

displayS :: SimpleDoc e -> ShowS #

`(displayS simpleDoc)` takes the output `simpleDoc` from a rendering function and transforms it to a `ShowS` type (for use in the `Show` class).

    showWidth :: Int -> Doc -> String
    showWidth w x   = displayS (renderPretty 0.4 w x) ""

displayIO :: Handle -> SimpleDoc e -> IO () #

`(displayIO handle simpleDoc)` writes `simpleDoc` to the file handle `handle`. This function is used for example by `hPutDoc`:

    hPutDoc handle doc  = displayIO handle (renderPretty 0.4 100 doc)

# Undocumented

column :: (Int -> Doc e) -> Doc e #

nesting :: (Int -> Doc e) -> Doc e #

width :: Doc e -> (Int -> Doc e) -> Doc e #

columns :: (Int -> Doc e) -> Doc e #

ribbon :: (Int -> Doc e) -> Doc e #

# Re-exported standard functions

empty :: Alternative f => forall a. f a #

The identity of `<|>`

(<>) :: Semigroup a => a -> a -> a #

An associative operation.

    (a <> b) <> c = a <> (b <> c)

If `a` is also a `Monoid` we further require

    (<>) = mappend