Text.PrettyPrint.HughesPJ

pretty-1.1.2.0: Pretty-printing library

Copyright | (c) The University of Glasgow 2001
License | BSD-style (see the file LICENSE)
Maintainer | David Terei <code@davidterei.com>
Stability | stable
Portability | portable
Safe Haskell | Safe
Language | Haskell98

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
- Utility functions for 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

Synopsis

- data Doc
- data TextDetails
  - = Chr !Char
  - | Str String
  - | PStr String
- char :: Char -> Doc
- text :: String -> Doc
- ptext :: String -> Doc
- sizedText :: Int -> 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
- maybeParens :: Bool -> Doc -> Doc
- maybeBrackets :: Bool -> Doc -> Doc
- maybeBraces :: Bool -> Doc -> Doc
- maybeQuotes :: Bool -> Doc -> Doc
- maybeDoubleQuotes :: Bool -> 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
- first :: Doc -> Doc -> Doc
- reduceDoc :: Doc -> RDoc
- render :: Doc -> String
- data Style = Style {
  - mode :: Mode
  - lineLength :: Int
  - ribbonsPerLine :: Float
  }
- style :: Style
- renderStyle :: Style -> Doc -> String
- data Mode
  - = PageMode
  - | ZigZagMode
  - | LeftMode
  - | OneLineMode
- fullRender :: Mode -> Int -> Float -> (TextDetails -> a -> a) -> a -> Doc -> a

# 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

Eq Doc |
Show Doc |
IsString Doc |
Generic Doc |
Monoid Doc |
NFData Doc |
type Rep Doc |

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.

Instances

Eq TextDetails |
Show TextDetails |
Generic TextDetails |
NFData TextDetails |
type Rep TextDetails |

# 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 `"..."`

maybeParens :: Bool -> Doc -> Doc

Apply `parens` to `Doc` if boolean is true.

maybeBrackets :: Bool -> Doc -> Doc

Apply `brackets` to `Doc` if boolean is true.

maybeBraces :: Bool -> Doc -> Doc

Apply `braces` to `Doc` if boolean is true.

maybeQuotes :: Bool -> Doc -> Doc

Apply `quotes` to `Doc` if boolean is true.

maybeDoubleQuotes :: Bool -> Doc -> Doc

Apply `doubleQuotes` to `Doc` if boolean is true.

## 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 infixl 6

Beside. `<>` is associative, with identity `empty`.

(<+>) :: Doc -> Doc -> Doc infixl 6

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 infixl 5

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 infixl 5

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

# Utility functions for documents

first :: Doc -> Doc -> Doc

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

reduceDoc :: Doc -> RDoc

Perform some simplification of a built up `GDoc`.

# 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 line length to ribbon length

Instances

Eq Style |
Show Style |
Generic Style |
type Rep Style |

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`.

data Mode

Rendering mode.

Constructors

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

Instances

Eq Mode |
Show Mode |
Generic Mode |
type Rep Mode |

## 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.