Text.PrettyPrint.ANSI.Leijen

ansi-wl-pprint-0.6.8.2: 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 | Edward Kmett <ekmett@gmail.com>
Stability | provisional
Portability | portable
Safe Haskell | Safe
Language | Haskell2010

Text.PrettyPrint.ANSI.Leijen

Contents

- The algebra of pretty-printing
- Documents
- Basic combinators
- Alignment combinators
- Operators
- List combinators
- Filler combinators
- Bracketing combinators
- Named character combinators
- ANSI formatting combinators
  - Forecolor combinators
  - Backcolor combinators
  - Emboldening combinators
  - Underlining combinators
  - Formatting elimination combinators
- Pretty class
- Rendering and displaying documents
  - Simple (i.e., rendered) documents
  - Simultaneous rendering and displaying of documents
- Undocumented

Description

This module is an extended implementation of the functional pretty printer given by Philip Wadler (1997):

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

In their bare essence, the combinators given by Wadler are not expressive enough to describe some commonly occurring layouts. This 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. 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.
- There are many additional useful combinators, like `fillSep` and `list`.
- There are two renderers: `renderPretty` for pretty printing, and `renderCompact` for quickly rendered, compact output more suitable for generating input to other programs.
- The pretty printing algorithm used by `renderPretty` extends the algorithm given by Wadler to take into account a "ribbon width", i.e., a desired maximum number of non-indentation characters to output on any one line.
- 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.
- The library has been extended to allow formatting text for output to ANSI style consoles. New combinators allow control of foreground and background color and the ability to make parts of the text bold or underlined.

Synopsis

- data Doc
- empty :: Doc
- char :: Char -> Doc
- text :: String -> Doc
- string :: String -> Doc
- int :: Int -> Doc
- integer :: Integer -> Doc
- float :: Float -> Doc
- double :: Double -> Doc
- rational :: Rational -> Doc
- bool :: Bool -> Doc
- (<>) :: Semigroup a => a -> a -> a
- nest :: Int -> Doc -> Doc
- line :: Doc
- linebreak :: Doc
- group :: Doc -> Doc
- softline :: Doc
- softbreak :: Doc
- hardline :: Doc
- flatAlt :: Doc -> Doc -> Doc
- 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
- 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
- renderSmart :: Float -> Int -> Doc -> SimpleDoc
- displayS :: SimpleDoc -> ShowS
- displayIO :: Handle -> SimpleDoc -> IO ()
- putDoc :: Doc -> IO ()
- hPutDoc :: Handle -> Doc -> IO ()
- column :: (Int -> Doc) -> Doc
- columns :: (Maybe Int -> Doc) -> Doc
- nesting :: (Int -> Doc) -> Doc
- width :: Doc -> (Int -> Doc) -> Doc

# The algebra of pretty-printing

The combinators in this library satisfy many algebraic laws.

The concatenation operator `<>` is associative and has `empty` as a left and right unit:

    x <> (y <> z)           = (x <> y) <> z
    x <> empty              = x
    empty <> x              = x

The `text` combinator is a homomorphism from string concatenation to document concatenation:

    text (s ++ t)           = text s <> text t
    text ""                 = empty

The `char` combinator behaves like one-element text:

    char c                  = text [c]

The `nest` combinator is a homomorphism from addition to document composition. `nest` also distributes through document concatenation and is absorbed by `text` and `align`:

    nest (i + j) x          = nest i (nest j x)
    nest 0 x                = x
    nest i (x <> y)         = nest i x <> nest i y
    nest i empty            = empty
    nest i (text s)         = text s
    nest i (align x)        = align x

The `group` combinator is absorbed by `empty`. `group` is commutative with `nest` and `align`:

    group empty             = empty
    group (text s <> x)     = text s <> group x
    group (nest i x)        = nest i (group x)
    group (align x)         = align (group x)

The `align` combinator is absorbed by `empty` and `text`. `align` is idempotent:

    align empty             = empty
    align (text s)          = text s
    align (align x)         = align x

From the laws of the primitive combinators, we can derive many other laws for the derived combinators. For example, the above operator `<$>` is defined as:

    x <$> y                 = x <> line <> y

It follows that `<$>` is associative and that `<$>` and `<>` associate with each other:

    x <$> (y <$> z)         = (x <$> y) <$> z
    x <> (y <$> z)          = (x <> y) <$> z
    x <$> (y <> z)          = (x <$> y) <> z

Similar laws also hold for the other line break operators `</>`, `<$$>`, and `<//>`.

# Documents

data Doc #

The abstract data type `Doc` represents pretty documents.

More specifically, a value of type `Doc` represents a non-empty set of possible renderings of a document. The rendering functions select one of these possibilities.

`Doc` is an instance of the `Show` class. `(show doc)` pretty prints document `doc` with a page width of 80 characters and a ribbon width of 32 characters.

    show (text "hello" <$> text "world")

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

    hello
    world

Instances

Show Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods showsPrec :: Int -> Doc -> ShowS # show :: Doc -> String # showList :: [Doc] -> ShowS #
IsString Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods fromString :: String -> Doc #
Semigroup Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods (<>) :: Doc -> Doc -> Doc # sconcat :: NonEmpty Doc -> Doc # stimes :: Integral b => b -> Doc -> Doc #
Monoid Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods mempty :: Doc # mappend :: Doc -> Doc -> Doc # mconcat :: [Doc] -> Doc #
Pretty Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Doc -> Doc # prettyList :: [Doc] -> Doc #

# 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.

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`.

bool :: Bool -> Doc #

The document `(bool b)` shows the literal bool `b` using `text`.

(<>) :: Semigroup a => a -> a -> a infixr 6 #

An associative operation.

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.

# Alignment combinators

The combinators in this section cannot be described by Wadler's original combinators. They align their output relative to the current output position — in contrast to `nest` which always aligns to the current nesting level. This deprives these combinators from being `optimal'. In practice however they prove to be very useful. The combinators in this section should be used with care, since they are more expensive than the other combinators. For example, `align` shouldn't be used to pretty print all top-level declarations of a language, but using `hang` for let expressions is fine.

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 semicolons and encloses them in braces. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All semicolons 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`.)

# Filler combinators

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 "]".

# Named character combinators

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 semicolon, ";".

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, "=".

# ANSI formatting combinators

This terminal formatting functionality is, as far as possible, portable across platforms with their varying terminals. However, note that to display ANSI colors and formatting will only be displayed on Windows consoles if the `Doc` value is output using the `putDoc` function or one of its friends. Rendering the `Doc` to a `String` and then outputing that will only work on Unix-style operating systems.

## Forecolor 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

## Backcolor combinators

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 black 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

## Formatting elimination combinators

plain :: Doc -> Doc #

Removes all colorisation, emboldening and underlining from a document

# 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 # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Bool -> Doc # prettyList :: [Bool] -> Doc #
Pretty Char # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Char -> Doc # prettyList :: [Char] -> Doc #
Pretty Double # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Double -> Doc # prettyList :: [Double] -> Doc #
Pretty Float # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Float -> Doc # prettyList :: [Float] -> Doc #
Pretty Int # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Int -> Doc # prettyList :: [Int] -> Doc #
Pretty Integer # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Integer -> Doc # prettyList :: [Integer] -> Doc #
Pretty () # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: () -> Doc # prettyList :: [()] -> Doc #
Pretty Doc # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Doc -> Doc # prettyList :: [Doc] -> Doc #
Pretty a => Pretty [a] # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: [a] -> Doc # prettyList :: [[a]] -> Doc #
Pretty a => Pretty (Maybe a) # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: Maybe a -> Doc # prettyList :: [Maybe a] -> Doc #
(Pretty a, Pretty b) => Pretty (a, b) # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: (a, b) -> Doc # prettyList :: [(a, b)] -> Doc #
(Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) # |
Instance details Defined in Text.PrettyPrint.ANSI.Leijen.Internal Methods pretty :: (a, b, c) -> Doc # prettyList :: [(a, b, c)] -> Doc #

# Rendering and displaying documents

## Simple (i.e., rendered) documents

data SimpleDoc #

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

Whereas values of the data type `Doc` represent non-empty sets of possible renderings of a document, values of the data type `SimpleDoc` represent single renderings of a document.

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.

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.

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 80 doc)

Any ANSI colorisation in `simpleDoc` will be output.

## Simultaneous rendering and displaying of documents

putDoc :: Doc -> IO () #

The action `(putDoc doc)` pretty prints document `doc` to the standard output, with a page width of 80 characters and a ribbon width of 32 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 80 characters and a ribbon width of 32 characters.

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

Any ANSI colorisation in `doc` will be output.

# Undocumented

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

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

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

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