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

Text.PrettyPrint.HughesPJ

Contents

The document type
Constructing documents
Predicates on documents
Utility functions for documents
Rendering documents

Description

John Hughes's and Simon Peyton Jones's Pretty Printer Combinators

Based on The Design of a Pretty-printing Library in Advanced Functional Programming, Johan Jeuring and Erik Meijer (eds), LNCS 925 http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps

Heavily modified by Simon Peyton Jones (December 1996).

Synopsis

The document type

data Doc Source

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

data TextDetails Source

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.

Constructing documents

Converting values into documents

char :: Char -> Doc Source

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

text :: String -> Doc Source

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 Source

Same as text. Used to be used for Bytestrings.

sizedText :: Int -> String -> Doc Source

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

zeroWidthText :: String -> Doc Source

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

int Source

Arguments

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

integer Source

Arguments

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

float Source

Arguments

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

double Source

Arguments

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

rational Source

Arguments

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

Simple derived documents

semi Source

Arguments

:: Doc

A ';' character

comma Source

Arguments

:: Doc

A ',' character

colon Source

Arguments

:: Doc

A : character

space Source

Arguments

:: Doc

A space character

equals Source

Arguments

:: Doc

A '=' character

lparen Source

Arguments

:: Doc

A '(' character

rparen Source

Arguments

:: Doc

A ')' character

lbrack Source

Arguments

:: Doc

A '[' character

rbrack Source

Arguments

:: Doc

A ']' character

lbrace Source

Arguments

:: Doc

A '{' character

rbrace Source

Arguments

:: Doc

A '}' character

Wrapping documents in delimiters

parens Source

Arguments

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

brackets Source

Arguments

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

braces Source

Arguments

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

quotes Source

Arguments

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

doubleQuotes Source

Arguments

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

Combining documents

empty :: Doc Source

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 Source

Beside. <> is associative, with identity empty.

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

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

hcat :: [Doc] -> Doc Source

List version of <>.

hsep :: [Doc] -> Doc Source

List version of <+>.

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

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 Source

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

vcat :: [Doc] -> Doc Source

List version of $$.

sep :: [Doc] -> Doc Source

Either hsep or vcat.

cat :: [Doc] -> Doc Source

Either hcat or vcat.

fsep :: [Doc] -> Doc Source

"Paragraph fill" version of sep.

fcat :: [Doc] -> Doc Source

"Paragraph fill" version of cat.

nest :: Int -> Doc -> Doc Source

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 Source

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

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

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

Predicates on documents

isEmpty :: Doc -> Bool Source

Returns True if the document is empty

Utility functions for documents

first :: Doc -> Doc -> Doc Source

first returns its first argument if it is non-empty, otherwise its second.

reduceDoc :: Doc -> RDoc aSource

Perform some simplification of a built up GDoc.

Rendering documents

Default rendering

render :: Doc -> String Source

Render the Doc to a String using the default Style.

Rendering with a particular style

data Style Source

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 Source

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

renderStyle :: Style -> Doc -> String Source

Render the Doc to a String using the given Style.

data Mode Source

Rendering mode.

Constructors

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

General rendering

fullRender Source

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.