ansi-wl-pprint-0.6.9: The Wadler/Leijen Pretty Printer for colored ANSI terminal output

Copyright Daan Leijen (c) 2000 http://www.cs.uu.nl/~daanMax Bolingbroke (c) 2008 http://blog.omega-prime.co.uk BSD-style (see the file LICENSE) Edward Kmett provisional portable Safe Haskell2010

Text.PrettyPrint.ANSI.Leijen

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.


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 document (x <> y) concatenates document x and y with a linebreak in between. (infixr 5) (<//>) :: Doc -> Doc -> Doc infixr 5 Source # 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 Source # The document (hsep xs) concatenates all documents xs horizontally with (<+>). vsep :: [Doc] -> Doc Source # 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 Source # 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 Source # 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 Source # The document (hcat xs) concatenates all documents xs horizontally with (<>). vcat :: [Doc] -> Doc Source # 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 Source #

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 Source #

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] Source #

(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 Source #

The document (fill i x) renders document x. It than appends spaces 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


The document (fillBreak i x) first renders document x. It than appends spaces 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 Source #

The document (enclose l r x) encloses document x between documents l and r using (<>).

enclose l r x   = l <> x <> r

Document (squotes x) encloses document x with single quotes "'".

Document (dquotes x) encloses document x with double quotes '"'.

Document (parens x) encloses document x in parenthesis, "(" and ")".

Document (angles x) encloses document x in angles, "<" and ">".

Document (braces x) encloses document x in braces, "{" and "}".

Document (brackets x) encloses document x in square brackets, "[" and "]".

# Named character combinators

The document lparen contains a left parenthesis, "(".

The document rparen contains a right parenthesis, ")".

The document langle contains a left angle, "<".

The document rangle contains a right angle, ">".

The document lbrace contains a left brace, "{".

The document rbrace contains a right brace, "}".

The document lbracket contains a left square bracket, "[".

The document rbracket contains a right square bracket, "]".

The document squote contains a single quote, "'".

The document dquote contains a double quote, '"'.

The document semi contains a semicolon, ";".

The document colon contains a colon, ":".

The document comma contains a comma, ",".

The document space contains a single space, " ".

x <+> y   = x <> space <> y

The document dot contains a single dot, ".".

The document backslash contains a back slash, "\".

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

Displays a document with the black forecolor

red :: Doc -> Doc Source #

Displays a document with the red forecolor

Displays a document with the green forecolor

Displays a document with the yellow forecolor

Displays a document with the blue forecolor

Displays a document with the magenta forecolor

Displays a document with the cyan forecolor

Displays a document with the white forecolor

Displays a document with the dull black forecolor

Displays a document with the dull red forecolor

Displays a document with the dull green forecolor

Displays a document with the dull yellow forecolor

Displays a document with the dull blue forecolor

Displays a document with the dull magenta forecolor

Displays a document with the dull cyan forecolor

Displays a document with the dull white forecolor

## Backcolor combinators

Displays a document with the black backcolor

Displays a document with the red backcolor

Displays a document with the green backcolor

Displays a document with the yellow backcolor

Displays a document with the blue backcolor

Displays a document with the magenta backcolor

Displays a document with the cyan backcolor

Displays a document with the white backcolor

Displays a document with the dull black backcolor

Displays a document with the dull red backcolor

Displays a document with the dull green backcolor

Displays a document with the dull yellow backcolor

Displays a document with the dull blue backcolor

Displays a document with the dull magenta backcolor

Displays a document with the dull cyan backcolor

Displays a document with the dull white backcolor

## Emboldening combinators

Displays a document in a heavier font weight

Displays a document in the normal font weight

## Underlining combinators

Displays a document with underlining

Displays a document with no underlining

## Formatting elimination combinators

Removes all colorisation, emboldening and underlining from a document

# Pretty class

class Pretty a where Source #

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 Source #

prettyList :: [a] -> Doc Source #

Instances
 Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Bool] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Char] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Double] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Float] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Int] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Integer] -> Doc Source # Pretty () Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal Methodspretty :: () -> Doc Source #prettyList :: [()] -> Doc Source # Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal MethodsprettyList :: [Doc] -> Doc Source # Pretty a => Pretty [a] Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal Methodspretty :: [a] -> Doc Source #prettyList :: [[a]] -> Doc Source # Pretty a => Pretty (Maybe a) Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal Methodspretty :: Maybe a -> Doc Source #prettyList :: [Maybe a] -> Doc Source # (Pretty a, Pretty b) => Pretty (a, b) Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal Methodspretty :: (a, b) -> Doc Source #prettyList :: [(a, b)] -> Doc Source # (Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) Source # Instance detailsDefined in Text.PrettyPrint.ANSI.Leijen.Internal Methodspretty :: (a, b, c) -> Doc Source #prettyList :: [(a, b, c)] -> Doc Source #

# Rendering and displaying documents

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

data SimpleDoc Source #

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

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 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.

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) 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) 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 () Source #

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 () Source #

(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 Source #

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

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