Portability	portable
Stability	stable
Maintainer	David Terei <dave.terei@gmail.com>
Safe Haskell	Safe

Text.PrettyPrint

Contents

The document type
Constructing documents
Predicates on documents
Rendering documents

Description

The default interface to the pretty-printing library. Provides a collection of pretty printer combinators.

This module should be used as opposed to the Text.PrettyPrint.HughesPJ module. Both are equivalent though as this module simply re-exports the other.

Synopsis

The document type

data Doc

The abstract type of documents. A Doc represents a *set* of layouts. A Doc with no occurrences of Union or NoDoc represents just one layout.

Instances

Show Doc
IsString Doc
Monoid Doc

Constructing documents

Converting values into documents

char :: Char -> Doc

A document of height and width 1, containing a literal character.

text :: String -> Doc

A document of height 1 containing a literal string. text satisfies the following laws:

```
text s <> text t = text (s++t)
```
text "" <> x = x, if x non-empty

The side condition on the last law is necessary because text "" has height 1, while empty has no height.

ptext :: String -> Doc

Same as text. Used to be used for Bytestrings.

sizedText :: Int -> String -> Doc

Some text with any width. (text s = sizedText (length s) s)

zeroWidthText :: String -> Doc

Some text, but without any width. Use for non-printing text such as a HTML or Latex tags

int

Arguments

:: Int
-> Doc	int n = text (show n)

integer

Arguments

:: Integer
-> Doc	integer n = text (show n)

float

Arguments

:: Float
-> Doc	float n = text (show n)

double

Arguments

:: Double
-> Doc	double n = text (show n)

rational

Arguments

:: Rational
-> Doc	rational n = text (show n)

Simple derived documents

semi

Arguments

:: Doc

A ';' character

comma

Arguments

:: Doc

A ',' character

colon

Arguments

:: Doc

A : character

space

Arguments

:: Doc

A space character

equals

Arguments

:: Doc

A '=' character

lparen

Arguments

:: Doc

A '(' character

rparen

Arguments

:: Doc

A ')' character

lbrack

Arguments

:: Doc

A '[' character

rbrack

Arguments

:: Doc

A ']' character

lbrace

Arguments

:: Doc

A '{' character

rbrace

Arguments

:: Doc

A '}' character

Wrapping documents in delimiters

parens

Arguments

:: Doc
-> Doc	Wrap document in `(...)`

brackets

Arguments

:: Doc
-> Doc	Wrap document in `[...]`

braces

Arguments

:: Doc
-> Doc	Wrap document in `{...}`

quotes

Arguments

:: Doc
-> Doc	Wrap document in `'...'`

doubleQuotes

Arguments

:: Doc
-> Doc	Wrap document in `"..."`

Combining documents

empty :: Doc

The empty document, with no height and no width. empty is the identity for <>, <+>, $$ and $+$ , and anywhere in the argument list for sep, hcat, hsep, vcat, fcat etc.

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

Beside. <> is associative, with identity empty.

(<+>) :: Doc -> Doc -> Doc

Beside, separated by space, unless one of the arguments is empty. <+> is associative, with identity empty.

hcat :: [Doc] -> Doc

List version of <>.

hsep :: [Doc] -> Doc

List version of <+>.

($$) :: Doc -> Doc -> Doc

Above, except that if the last line of the first argument stops at least one position before the first line of the second begins, these two lines are overlapped. For example:

    text "hi" $$ nest 5 (text "there")

lays out as

    hi   there

rather than

    hi
         there

$$ is associative, with identity empty, and also satisfies

(x $$ y) <> z = x $$ (y <> z), if y non-empty.

($+$) :: Doc -> Doc -> Doc

Above, with no overlapping. $+$ is associative, with identity empty.

vcat :: [Doc] -> Doc

List version of $$.

sep :: [Doc] -> Doc

Either hsep or vcat.

cat :: [Doc] -> Doc

Either hcat or vcat.

fsep :: [Doc] -> Doc

"Paragraph fill" version of sep.

fcat :: [Doc] -> Doc

"Paragraph fill" version of cat.

nest :: Int -> Doc -> Doc

Nest (or indent) a document by a given number of positions (which may also be negative). nest satisfies the laws:

```
nest 0 x = x
```
```
nest k (nest k' x) = nest (k+k') x
```
```
nest k (x <> y) = nest k z <> nest k y
```
```
nest k (x $$ y) = nest k x $$ nest k y
```
```
nest k empty = empty
```
x <> nest k y = x <> y, if x non-empty

The side condition on the last law is needed because empty is a left identity for <>.

hang :: Doc -> Int -> Doc -> Doc

hang d1 n d2 = sep [d1, nest n d2]

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

punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]

Predicates on documents

isEmpty :: Doc -> Bool

Returns True if the document is empty

Rendering documents

Default rendering

render :: Doc -> String

Render the Doc to a String using the default Style.

Rendering with a particular style

data Style

A rendering style.

Constructors

Style
Fields mode :: Mode The rendering mode lineLength :: Int Length of line, in chars ribbonsPerLine :: Float Ratio of ribbon length to line length

style :: Style

The default style (mode=PageMode, lineLength=100, ribbonsPerLine=1.5).

renderStyle :: Style -> Doc -> String

Render the Doc to a String using the given Style.

General rendering

fullRender

Arguments

:: Mode	Rendering mode
-> Int	Line length
-> Float	Ribbons per line
-> (TextDetails -> a -> a)	What to do with text
-> a	What to do at the end
-> Doc	The document
-> a	Result

The general rendering interface.

data Mode

Rendering mode.

Constructors

PageMode	Normal
ZigZagMode	With zig-zag cuts
LeftMode	No indentation, infinitely long lines
OneLineMode	All on one line

data TextDetails

The TextDetails data type

A TextDetails represents a fragment of text that will be output at some point.

Constructors

Chr !Char	A single Char fragment
Str String	A whole String fragment
PStr String	Used to represent a Fast String fragment but now deprecated and identical to the Str constructor.