Text.PrettyPrint.ANSI.Leijen

ansi-wl-pprint-0.6.7.3: The Wadler/Leijen Pretty Printer for colored ANSI terminal output

Copyright | Daan Leijen (c) 2000, http://www.cs.uu.nl/~daan Max Bolingbroke (c) 2008, http://blog.omega-prime.co.uk
License | BSD-style (see the file LICENSE)
Maintainer | batterseapower@hotmail.com
Stability | provisional
Portability | portable
Safe Haskell | Safe
Language | Haskell98

Text.PrettyPrint.ANSI.Leijen

Contents

- Documents
- Basic combinators
- Alignment
- Operators
- List combinators
- Fillers
- Bracketing combinators
- Character documents
- Colorisation combinators
- Emboldening combinators
- Underlining combinators
- Removing formatting
- Primitive type documents
- Pretty class
- Rendering
- Undocumented

Description

Pretty print module based on Philip Wadler's "prettier printer"

         "A prettier printer"
         Draft paper, April 1997, revised March 1998.
         http://cm.bell-labs.com/cm/cs/who/wadler/papers/prettier/prettier.ps

PPrint 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 above combinator is called `<$>`. 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 displayers, `displayS` for strings and `displayIO` for file based output.
- There is a `Pretty` class.
- The implementation uses optimised representations and strictness annotations.

Full documentation for the original wl-pprint library available at http://www.cs.uu.nl/~daan/download/pprint/pprint.html.

The library has been extended to allow formatting text for output to ANSI style consoles. New combinators allow:

- Control of foreground and background color of text
- The abliity to make parts of the text bold or underlined

This functionality is, as far as possible, portable across platforms with their varying terminals. However, one thing to be particularly wary of is that console colors will not be displayed on Windows unless the `Doc` value is output using the `putDoc` function or one of it's friends. Rendering the `Doc` to a `String` and then outputing that will only work on Unix-style operating systems.

Synopsis

- data Doc
- putDoc :: Doc -> IO ()
- hPutDoc :: Handle -> Doc -> IO ()
- empty :: Doc
- char :: Char -> Doc
- text :: String -> Doc
- (<>) :: Doc -> Doc -> Doc
- nest :: Int -> Doc -> Doc
- line :: Doc
- linebreak :: Doc
- group :: Doc -> Doc
- softline :: Doc
- softbreak :: Doc
- hardline :: Doc
- flatAlt :: Doc -> Doc -> Doc
- renderSmart :: Float -> Int -> Doc -> SimpleDoc
- align :: Doc -> Doc
- hang :: Int -> Doc -> Doc
- indent :: Int -> Doc -> Doc
- encloseSep :: Doc -> Doc -> Doc -> [Doc] -> Doc
- list :: [Doc] -> Doc
- tupled :: [Doc] -> Doc
- semiBraces :: [Doc] -> Doc
- (<+>) :: Doc -> Doc -> Doc
- (<$>) :: Doc -> Doc -> Doc
- (</>) :: Doc -> Doc -> Doc
- (<$$>) :: Doc -> Doc -> Doc
- (<//>) :: Doc -> Doc -> Doc
- hsep :: [Doc] -> Doc
- vsep :: [Doc] -> Doc
- fillSep :: [Doc] -> Doc
- sep :: [Doc] -> Doc
- hcat :: [Doc] -> Doc
- vcat :: [Doc] -> Doc
- fillCat :: [Doc] -> Doc
- cat :: [Doc] -> Doc
- punctuate :: Doc -> [Doc] -> [Doc]
- fill :: Int -> Doc -> Doc
- fillBreak :: Int -> Doc -> Doc
- enclose :: Doc -> Doc -> Doc -> Doc
- squotes :: Doc -> Doc
- dquotes :: Doc -> Doc
- parens :: Doc -> Doc
- angles :: Doc -> Doc
- braces :: Doc -> Doc
- brackets :: Doc -> Doc
- lparen :: Doc
- rparen :: Doc
- langle :: Doc
- rangle :: Doc
- lbrace :: Doc
- rbrace :: Doc
- lbracket :: Doc
- rbracket :: Doc
- squote :: Doc
- dquote :: Doc
- semi :: Doc
- colon :: Doc
- comma :: Doc
- space :: Doc
- dot :: Doc
- backslash :: Doc
- equals :: Doc
- black :: Doc -> Doc
- red :: Doc -> Doc
- green :: Doc -> Doc
- yellow :: Doc -> Doc
- blue :: Doc -> Doc
- magenta :: Doc -> Doc
- cyan :: Doc -> Doc
- white :: Doc -> Doc
- dullblack :: Doc -> Doc
- dullred :: Doc -> Doc
- dullgreen :: Doc -> Doc
- dullyellow :: Doc -> Doc
- dullblue :: Doc -> Doc
- dullmagenta :: Doc -> Doc
- dullcyan :: Doc -> Doc
- dullwhite :: Doc -> Doc
- onblack :: Doc -> Doc
- onred :: Doc -> Doc
- ongreen :: Doc -> Doc
- onyellow :: Doc -> Doc
- onblue :: Doc -> Doc
- onmagenta :: Doc -> Doc
- oncyan :: Doc -> Doc
- onwhite :: Doc -> Doc
- ondullblack :: Doc -> Doc
- ondullred :: Doc -> Doc
- ondullgreen :: Doc -> Doc
- ondullyellow :: Doc -> Doc
- ondullblue :: Doc -> Doc
- ondullmagenta :: Doc -> Doc
- ondullcyan :: Doc -> Doc
- ondullwhite :: Doc -> Doc
- bold :: Doc -> Doc
- debold :: Doc -> Doc
- underline :: Doc -> Doc
- deunderline :: Doc -> Doc
- plain :: Doc -> Doc
- string :: String -> Doc
- int :: Int -> Doc
- integer :: Integer -> Doc
- float :: Float -> Doc
- double :: Double -> Doc
- rational :: Rational -> Doc
- class Pretty a where
  - pretty :: a -> Doc
  - prettyList :: [a] -> Doc
- data SimpleDoc
  - = SFail
  - | SEmpty
  - | SChar Char SimpleDoc
  - | SText !Int String SimpleDoc
  - | SLine !Int SimpleDoc
  - | SSGR [SGR] SimpleDoc
- renderPretty :: Float -> Int -> Doc -> SimpleDoc
- renderCompact :: Doc -> SimpleDoc
- displayS :: SimpleDoc -> ShowS
- displayIO :: Handle -> SimpleDoc -> IO ()
- bool :: Bool -> Doc
- column :: (Int -> Doc) -> Doc
- columns :: (Maybe Int -> Doc) -> Doc
- nesting :: (Int -> Doc) -> Doc
- width :: Doc -> (Int -> Doc) -> Doc

# Documents

data Doc

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" <$> text "world")

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

    hello
    world

Instances

Show Doc |
IsString Doc |
Monoid Doc |
Pretty Doc |

putDoc :: Doc -> 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

Any ANSI colorisation in `doc` will be output.

hPutDoc :: Handle -> Doc -> 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
             }

Any ANSI colorisation in `doc` will be output.

# Basic combinators

empty :: Doc

The empty document is, indeed, empty. Although `empty` has no content, it does have a 'height' of 1 and behaves exactly like `(text "")` (and is therefore not a unit of `<$>`).

char :: Char -> Doc

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

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.

(<>) :: Doc -> Doc -> Doc infixr 6

The document `(x <> y)` concatenates document `x` and document `y`. It is an associative operation having `empty` as a left and right unit. (infixr 6)

nest :: Int -> Doc -> Doc

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" <$> text "world") <$> text "!"

outputs as:

    hello
      world
    !

line :: Doc

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

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 -> Doc

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

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

    softline = group line

softbreak :: Doc

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

    softbreak  = group linebreak

hardline :: Doc

A linebreak that will never be flattened; it is guaranteed to render as a newline.

flatAlt :: Doc -> Doc -> Doc

A document that is normally rendered as the first argument, but when flattened, is rendered as the second document.

renderSmart :: Float -> Int -> Doc -> SimpleDoc

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 20 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 20-c mark. In contrast, `renderSmart` will continue to check that 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. boundary.

# Alignment

align :: Doc -> Doc

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 (x <$> y)

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

which will be layed out as:

    hi nice
       world

hang :: Int -> Doc -> Doc

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 -> Doc

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 :: Doc -> Doc -> Doc -> [Doc] -> Doc

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 :: [Doc] -> Doc

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 :: [Doc] -> Doc

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 :: [Doc] -> Doc

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 -> Doc -> Doc infixr 6

The document `(x <+> y)` concatenates document `x` and `y` with a `space` in between. (infixr 6)

(<$>) :: Doc -> Doc -> Doc infixr 5

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

(</>) :: Doc -> Doc -> Doc 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)

(<$$>) :: Doc -> Doc -> Doc infixr 5

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

(<//>) :: Doc -> Doc -> Doc 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 :: [Doc] -> Doc

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

vsep :: [Doc] -> Doc

The document `(vsep xs)` concatenates all documents `xs` vertically with `(<$>)`. 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 :: [Doc] -> Doc

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

    fillSep xs  = foldr (\<\/\>) empty xs

sep :: [Doc] -> Doc

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

    sep xs  = group (vsep xs)

hcat :: [Doc] -> Doc

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

vcat :: [Doc] -> Doc

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

fillCat :: [Doc] -> Doc

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

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

cat :: [Doc] -> Doc

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

    cat xs  = group (vcat xs)

punctuate :: Doc -> [Doc] -> [Doc]

`(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 -> Doc

The document `(fill i x)` renders document `x`. It than 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")
             ,("nest","Int -> Doc -> Doc")
             ,("linebreak","Doc")]

    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
        nest   :: Int -> Doc -> Doc
        linebreak :: Doc

fillBreak :: Int -> Doc -> Doc

The document `(fillBreak i x)` first renders document `x`. It than 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
        nest   :: Int -> Doc -> Doc
        linebreak
               :: Doc

# Bracketing combinators

enclose :: Doc -> Doc -> Doc -> Doc

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

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

squotes :: Doc -> Doc

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

dquotes :: Doc -> Doc

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

parens :: Doc -> Doc

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

angles :: Doc -> Doc

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

braces :: Doc -> Doc

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

brackets :: Doc -> Doc

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

# Character documents

lparen :: Doc

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

rparen :: Doc

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

langle :: Doc

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

rangle :: Doc

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

lbrace :: Doc

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

rbrace :: Doc

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

lbracket :: Doc

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

rbracket :: Doc

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

squote :: Doc

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

dquote :: Doc

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

semi :: Doc

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

colon :: Doc

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

comma :: Doc

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

space :: Doc

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

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

dot :: Doc

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

backslash :: Doc

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

equals :: Doc

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

# Colorisation combinators

black :: Doc -> Doc

Displays a document with the black forecolor

red :: Doc -> Doc

Displays a document with the red forecolor

green :: Doc -> Doc

Displays a document with the green forecolor

yellow :: Doc -> Doc

Displays a document with the yellow forecolor

blue :: Doc -> Doc

Displays a document with the blue forecolor

magenta :: Doc -> Doc

Displays a document with the magenta forecolor

cyan :: Doc -> Doc

Displays a document with the cyan forecolor

white :: Doc -> Doc

Displays a document with the white forecolor

dullblack :: Doc -> Doc

Displays a document with the dull black forecolor

dullred :: Doc -> Doc

Displays a document with the dull red forecolor

dullgreen :: Doc -> Doc

Displays a document with the dull green forecolor

dullyellow :: Doc -> Doc

Displays a document with the dull yellow forecolor

dullblue :: Doc -> Doc

Displays a document with the dull blue forecolor

dullmagenta :: Doc -> Doc

Displays a document with the dull magenta forecolor

dullcyan :: Doc -> Doc

Displays a document with the dull cyan forecolor

dullwhite :: Doc -> Doc

Displays a document with the dull white forecolor

onblack :: Doc -> Doc

Displays a document with the black backcolor

onred :: Doc -> Doc

Displays a document with the red backcolor

ongreen :: Doc -> Doc

Displays a document with the green backcolor

onyellow :: Doc -> Doc

Displays a document with the yellow backcolor

onblue :: Doc -> Doc

Displays a document with the blue backcolor

onmagenta :: Doc -> Doc

Displays a document with the magenta backcolor

oncyan :: Doc -> Doc

Displays a document with the cyan backcolor

onwhite :: Doc -> Doc

Displays a document with the white backcolor

ondullblack :: Doc -> Doc

Displays a document with the dull block backcolor

ondullred :: Doc -> Doc

Displays a document with the dull red backcolor

ondullgreen :: Doc -> Doc

Displays a document with the dull green backcolor

ondullyellow :: Doc -> Doc

Displays a document with the dull yellow backcolor

ondullblue :: Doc -> Doc

Displays a document with the dull blue backcolor

ondullmagenta :: Doc -> Doc

Displays a document with the dull magenta backcolor

ondullcyan :: Doc -> Doc

Displays a document with the dull cyan backcolor

ondullwhite :: Doc -> Doc

Displays a document with the dull white backcolor

# Emboldening combinators

bold :: Doc -> Doc

Displays a document in a heavier font weight

debold :: Doc -> Doc

Displays a document in the normal font weight

# Underlining combinators

underline :: Doc -> Doc

Displays a document with underlining

deunderline :: Doc -> Doc

Displays a document with no underlining

# Removing formatting

plain :: Doc -> Doc

Removes all colorisation, emboldening and underlining from a document

# Primitive type documents

string :: String -> Doc

The document `(string s)` concatenates all characters in `s` using `line` for newline characters and `char` for all other characters. It is used instead of `text` whenever the text contains newline characters.

int :: Int -> Doc

The document `(int i)` shows the literal integer `i` using `text`.

integer :: Integer -> Doc

The document `(integer i)` shows the literal integer `i` using `text`.

float :: Float -> Doc

The document `(float f)` shows the literal float `f` using `text`.

double :: Double -> Doc

The document `(double d)` shows the literal double `d` using `text`.

rational :: Rational -> Doc

The document `(rational r)` shows the literal rational `r` using `text`.

# 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

prettyList :: [a] -> Doc

Instances

Pretty Bool |
Pretty Char |
Pretty Double |
Pretty Float |
Pretty Int |
Pretty Integer |
Pretty () |
Pretty Doc |
Pretty a => Pretty [a] |
Pretty a => Pretty (Maybe a) |
(Pretty a, Pretty b) => Pretty (a, b) |
(Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) |

# Rendering

data SimpleDoc

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 |
SText !Int String SimpleDoc |
SLine !Int SimpleDoc |
SSGR [SGR] SimpleDoc |

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

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 -> SimpleDoc

`(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.

This rendering function does not add any colorisation information.

displayS :: SimpleDoc -> 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) ""

ANSI color information will be discarded by this function unless you are running on a Unix-like operating system. This is due to a technical limitation in Windows ANSI support.

displayIO :: Handle -> SimpleDoc -> 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)

Any ANSI colorisation in `simpleDoc` will be output.

# Undocumented

bool :: Bool -> Doc

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

columns :: (Maybe Int -> Doc) -> Doc

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

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