annotated-wl-pprint-0.5.3: The Wadler/Leijen Pretty Printer, with annotation support

Safe HaskellNone

Text.PrettyPrint.Annotated.Leijen

Contents

Synopsis

Documents, parametrized by their annotations

data Doc a Source

The abstract data type Doc a represents pretty documents.

Doc a is an instance of the Show class. (show doc) pretty prints document doc with a page width of 100 characters and a ribbon width of 40 characters.

 show (text "hello" <$> text "world")

Which would return the string "hello\nworld", i.e.

 hello
 world

Instances

putDoc :: Doc a -> IO ()Source

The action (putDoc doc) pretty prints document doc to the standard output, with a page width of 100 characters and a ribbon width of 40 characters.

 main :: IO ()
 main = do{ putDoc (text "hello" <+> text "world") }

Which would output

 hello world

hPutDoc :: Handle -> Doc a -> IO ()Source

(hPutDoc handle doc) pretty prints document doc to the file handle handle with a page width of 100 characters and a ribbon width of 40 characters.

 main = do{ handle <- openFile "MyFile" WriteMode
          ; hPutDoc handle (vcat (map text
                            ["vertical","text"]))
          ; hClose handle
          }

Basic combinators

empty :: Doc aSource

The empty document is, indeed, empty. Although empty has no content, it does have a 'height' of 1 and behaves exactly like (text "") (and is therefore not a unit of <$>).

char :: Char -> Doc aSource

The document (char c) contains the literal character c. The character shouldn't be a newline ('\n'), the function line should be used for line breaks.

text :: String -> Doc aSource

The document (text s) contains the literal string s. The string shouldn't contain any newline ('\n') characters. If the string contains newline characters, the function string should be used.

(<>) :: Doc a -> Doc a -> Doc aSource

The document (x <> y) concatenates document x and document y. It is an associative operation having empty as a left and right unit. (infixr 6)

nest :: Int -> Doc a -> Doc aSource

The document (nest i x) renders document x with the current indentation level increased by i (See also hang, align and indent).

 nest 2 (text "hello" <$> text "world") <$> text "!"

outputs as:

 hello
   world
 !

line :: Doc aSource

The line document advances to the next line and indents to the current nesting level. Doc aument line behaves like (text " ") if the line break is undone by group.

linebreak :: Doc aSource

The linebreak document advances to the next line and indents to the current nesting level. Document linebreak behaves like empty if the line break is undone by group.

group :: Doc a -> Doc aSource

The group combinator is used to specify alternative layouts. The document (group x) undoes all line breaks in document x. The resulting line is added to the current line if that fits the page. Otherwise, the document x is rendered without any changes.

softline :: Doc aSource

The document softline behaves like space if the resulting output fits the page, otherwise it behaves like line.

 softline = group line

softbreak :: Doc aSource

The document softbreak behaves like empty if the resulting output fits the page, otherwise it behaves like line.

 softbreak  = group linebreak

Alignment

align :: Doc a -> Doc aSource

The document (align x) renders document x with the nesting level set to the current column. It is used for example to implement hang.

As an example, we will put a document right above another one, regardless of the current nesting level:

 x $$ y  = align (x <$> y)
 test    = text "hi" <+> (text "nice" $$ text "world")

which will be layed out as:

 hi nice
    world

hang :: Int -> Doc a -> Doc aSource

The hang combinator implements hanging indentation. The document (hang i x) renders document x with a nesting level set to the current column plus i. The following example uses hanging indentation for some text:

 test  = hang 4 (fillSep (map text
         (words "the hang combinator indents these words !")))

Which lays out on a page with a width of 20 characters as:

 the hang combinator
     indents these
     words !

The hang combinator is implemented as:

 hang i x  = align (nest i x)

indent :: Int -> Doc a -> Doc aSource

The document (indent i x) indents document x with i spaces.

 test  = indent 4 (fillSep (map text
         (words "the indent combinator indents these words !")))

Which lays out with a page width of 20 as:

     the indent
     combinator
     indents these
     words !

encloseSep :: Doc a -> Doc a -> Doc a -> [Doc a] -> Doc aSource

The document (encloseSep l r sep xs) concatenates the documents xs separated by sep and encloses the resulting document by l and r. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All separators are put in front of the elements. For example, the combinator list can be defined with encloseSep:

 list xs = encloseSep lbracket rbracket comma xs
 test    = text "list" <+> (list (map int [10,200,3000]))

Which is layed out with a page width of 20 as:

 list [10,200,3000]

But when the page width is 15, it is layed out as:

 list [10
      ,200
      ,3000]

list :: [Doc a] -> Doc aSource

The document (list xs) comma separates the documents xs and encloses them in square brackets. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All comma separators are put in front of the elements.

tupled :: [Doc a] -> Doc aSource

The document (tupled xs) comma separates the documents xs and encloses them in parenthesis. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All comma separators are put in front of the elements.

semiBraces :: [Doc a] -> Doc aSource

The document (semiBraces xs) separates the documents xs with semi colons and encloses them in braces. The documents are rendered horizontally if that fits the page. Otherwise they are aligned vertically. All semi colons are put in front of the elements.

Operators

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

The document (x <+> y) concatenates document x and y with a space in between. (infixr 6)

(<$>) :: Doc a -> Doc a -> Doc aSource

The document (x <$> y) concatenates document x and y with a line in between. (infixr 5)

(</>) :: Doc a -> Doc a -> Doc aSource

The document (x </> y) concatenates document x and y with a softline in between. This effectively puts x and y either next to each other (with a space in between) or underneath each other. (infixr 5)

(<$$>) :: Doc a -> Doc a -> Doc aSource

The document (x <$$> y) concatenates document x and y with a linebreak in between. (infixr 5)

(<//>) :: Doc a -> Doc a -> Doc aSource

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 a] -> Doc aSource

The document (hsep xs) concatenates all documents xs horizontally with (<+>).

vsep :: [Doc a] -> Doc aSource

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 a] -> Doc aSource

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 a] -> Doc aSource

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 a] -> Doc aSource

The document (hcat xs) concatenates all documents xs horizontally with (<>).

vcat :: [Doc a] -> Doc aSource

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 a] -> Doc aSource

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 a] -> Doc aSource

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 a -> [Doc a] -> [Doc a]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.)

Fillers

fill :: Int -> Doc a -> Doc aSource

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 a")
          ,("nest","Int -> Doc a -> Doc a")
          ,("linebreak","Doc a")]

 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 a
     nest   :: Int -> Doc a -> Doc a
     linebreak :: Doc a

fillBreak :: Int -> Doc a -> Doc aSource

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 a
     nest   :: Int -> Doc a -> Doc a
     linebreak
            :: Doc a

Bracketing combinators

enclose :: Doc a -> Doc a -> Doc a -> Doc aSource

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

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

squotes :: Doc a -> Doc aSource

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

dquotes :: Doc a -> Doc aSource

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

parens :: Doc a -> Doc aSource

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

angles :: Doc a -> Doc aSource

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

braces :: Doc a -> Doc aSource

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

brackets :: Doc a -> Doc aSource

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

Character documents

lparen :: Doc aSource

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

rparen :: Doc aSource

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

langle :: Doc aSource

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

rangle :: Doc aSource

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

lbrace :: Doc aSource

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

rbrace :: Doc aSource

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

lbracket :: Doc aSource

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

rbracket :: Doc aSource

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

squote :: Doc aSource

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

dquote :: Doc aSource

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

semi :: Doc aSource

The document semi contains a semi colon, ";".

colon :: Doc aSource

The document colon contains a colon, ":".

comma :: Doc aSource

The document comma contains a comma, ",".

space :: Doc aSource

The document space contains a single space, " ".

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

dot :: Doc aSource

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

backslash :: Doc aSource

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

equals :: Doc aSource

The document equals contains an equal sign, "=".

pipe :: Doc aSource

The document pipe contains a pipe character, "|".

Primitive type documents

string :: String -> Doc aSource

The document (string s) concatenates all characters in s using line for newline characters and char for all other characters. It is used instead of text whenever the text contains newline characters.

int :: Int -> Doc aSource

The document (int i) shows the literal integer i using text.

integer :: Integer -> Doc aSource

The document (integer i) shows the literal integer i using text.

float :: Float -> Doc aSource

The document (float f) shows the literal float f using text.

double :: Double -> Doc aSource

The document (double d) shows the literal double d using text.

rational :: Rational -> Doc aSource

The document (rational r) shows the literal rational r using text.

bool :: Bool -> Doc aSource

The document (bool b) is text True when b is true, and text False otherwise.

Pretty class

Semantic annotations

annotate :: a -> Doc a -> Doc aSource

noAnnotate :: Doc a -> Doc aSource

Strip annotations from a document. This is useful for re-using the textual formatting of some sub-document, but applying a different high-level annotation.

Rendering

data SimpleDoc a Source

The data type SimpleDoc a represents rendered documents and is used by the display functions.

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 a to your own output format.

Instances

renderPretty :: Float -> Int -> Doc a -> SimpleDoc aSource

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 :: Doc a -> SimpleDoc aSource

(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.

displayDecorated :: (a -> String -> String) -> SimpleDoc a -> StringSource

Render a string, where annotated regions are decorated by a user-provided function.

displayS :: SimpleDoc a -> ShowSSource

(displayS simpleDoc a) takes the output simpleDoc a from a rendering function and transforms it to a ShowS type (for use in the Show class).

 showWidth :: Int -> Doc a -> String
 showWidth w x   = displayS (renderPretty 0.4 w x) ""

displayIO :: Handle -> SimpleDoc a -> IO ()Source

(displayIO handle simpleDoc a) writes simpleDoc a to the file handle handle. This function is used for example by 'hPutDoc a':

 hPutDoc a handle doc  = displayIO handle (renderPretty 0.4 100 doc)

type SpanList a = [(Int, Int, a)]Source

displaySpans :: SimpleDoc a -> (String, SpanList a)Source

Generate a pair of a string and a list of source span/annotation pairs

Undocumented

column :: (Int -> Doc a) -> Doc aSource

nesting :: (Int -> Doc a) -> Doc aSource

width :: Doc a -> (Int -> Doc a) -> Doc aSource