Text.PrettyPrint.HughesPJ

pretty-1.0.1.2: Pretty-printing library

Portability | portable
Stability | provisional
Maintainer | libraries@haskell.org

Text.PrettyPrint.HughesPJ

Contents

- The document type
- Constructing documents
  - Converting values into documents
  - Simple derived documents
  - Wrapping documents in delimiters
  - Combining documents
- Predicates on documents
- Rendering documents
  - Default rendering
  - Rendering with a particular style
  - General rendering

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, Dec 96

Synopsis

- data Doc
- char :: Char -> Doc
- text :: String -> Doc
- ptext :: String -> Doc
- zeroWidthText :: String -> Doc
- int :: Int -> Doc
- integer :: Integer -> Doc
- float :: Float -> Doc
- double :: Double -> Doc
- rational :: Rational -> Doc
- semi :: Doc
- comma :: Doc
- colon :: Doc
- space :: Doc
- equals :: Doc
- lparen :: Doc
- rparen :: Doc
- lbrack :: Doc
- rbrack :: Doc
- lbrace :: Doc
- rbrace :: Doc
- parens :: Doc -> Doc
- brackets :: Doc -> Doc
- braces :: Doc -> Doc
- quotes :: Doc -> Doc
- doubleQuotes :: Doc -> Doc
- empty :: Doc
- (<>) :: Doc -> Doc -> Doc
- (<+>) :: Doc -> Doc -> Doc
- hcat :: [Doc] -> Doc
- hsep :: [Doc] -> Doc
- ($$) :: Doc -> Doc -> Doc
- ($+$) :: Doc -> Doc -> Doc
- vcat :: [Doc] -> Doc
- sep :: [Doc] -> Doc
- cat :: [Doc] -> Doc
- fsep :: [Doc] -> Doc
- fcat :: [Doc] -> Doc
- nest :: Int -> Doc -> Doc
- hang :: Doc -> Int -> Doc -> Doc
- punctuate :: Doc -> [Doc] -> [Doc]
- isEmpty :: Doc -> Bool
- render :: Doc -> String
- data Style = Style {
  - mode :: Mode
  - lineLength :: Int
  - ribbonsPerLine :: Float
  }
- style :: Style
- renderStyle :: Style -> Doc -> String
- fullRender :: Mode -> Int -> Float -> (TextDetails -> a -> a) -> a -> Doc -> a
- data Mode
  - = PageMode
  - | ZigZagMode
  - | LeftMode
  - | OneLineMode
- data TextDetails
  - = Chr Char
  - | Str String
  - | PStr String

# The document type

data Doc

The abstract type of documents. The `Show` instance is equivalent to using `render`.

Instances

Show 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

An obsolete function, now identical to `text`.

zeroWidthText :: String -> Doc

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

int :: Int -> Doc

    int n = text (show n)

integer :: Integer -> Doc

    integer n = text (show n)

float :: Float -> Doc

    float n = text (show n)

double :: Double -> Doc

    double n = text (show n)

rational :: Rational -> Doc

    rational n = text (show n)

## Simple derived documents

semi :: Doc

A ';' character

comma :: Doc

A ',' character

colon :: Doc

A `:` character

space :: Doc

A space character

equals :: Doc

A '=' character

lparen :: Doc

A '(' character

rparen :: Doc

A ')' character

lbrack :: Doc

A '[' character

rbrack :: Doc

A ']' character

lbrace :: Doc

A '{' character

rbrace :: Doc

A '}' character

## Wrapping documents in delimiters

parens :: Doc -> Doc

Wrap document in `(...)`

brackets :: Doc -> Doc

Wrap document in `[...]`

braces :: Doc -> Doc

Wrap document in `{...}`

quotes :: Doc -> Doc

Wrap document in `'...'`

doubleQuotes :: 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

Renders the document as 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 document as a string using a specified 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

Constructors

Chr Char |
Str String |
PStr String |