wl-pprint-text-1.2.0.0: A Wadler/Leijen Pretty Printer for Text values

Copyright Ivan Lazar Miljenovic (c) 2010Daan Leijen (c) 2000 http://www.cs.uu.nl/~daan BSD-style (see the file LICENSE) Ivan.Miljenovic@gmail.com provisional portable Safe Haskell98

Description

This module provides a version of Text.PrettyPrint.Leijen.Text where the combinators have been lifted into a Monad. The main usage for this is for state-based pretty-printing.

Synopsis

# Documents

data Doc Source #

The abstract data type Doc represents pretty documents.

Doc 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" <$> text "world") Which would return the string "hello\nworld", i.e.  hello world  Instances  Source # MethodsshowsPrec :: Int -> Doc -> ShowS #show :: Doc -> String #showList :: [Doc] -> ShowS # Source # Methods Source # In particular, note that the document (x <> y) concatenates document x and document y. It is an associative operation having empty as a left and right unit. (infixr 6) Methods(<>) :: Doc -> Doc -> Doc #stimes :: Integral b => b -> Doc -> Doc # Source # Methodsmappend :: Doc -> Doc -> Doc #mconcat :: [Doc] -> Doc # Source # MethodsprettyList :: [Doc] -> Doc Source # # Basic combinators empty :: Applicative m => m Doc Source # The empty document is, indeed, empty. Although empty has no content, it does have a 'height' of 1 and behaves exactly like (text "") (and is therefore not a unit of <$>).

char :: Applicative m => Char -> m Doc Source #

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 :: Applicative m => Text -> m Doc Source #

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.

beside :: Applicative m => m Doc -> m Doc -> m Doc infixr 6 Source #

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

nest :: Functor m => Int -> m Doc -> m Doc Source #

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 :: Applicative m => m Doc Source #

The line document advances to the next line and indents to the current nesting level. Document line behaves like (text " ") if the line break is undone by group or if rendered with renderOneLine.

linebreak :: Applicative m => m Doc Source #

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 :: Functor m => m Doc -> m Doc Source #

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 :: Applicative m => m Doc Source #

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

softbreak :: Applicative m => m Doc Source #

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

spacebreak :: Applicative m => m Doc Source #

The document spacebreak behaves like space when rendered normally but like empty when using renderCompact or renderOneLine.

# Alignment

The combinators in this section can not be described by Wadler's original combinators. They align their output relative to the current output position - in contrast to nest which always aligns to the current nesting level. This deprives these combinators from being optimal'. In practice however they prove to be very useful. The combinators in this section should be used with care, since they are more expensive than the other combinators. For example, align shouldn't be used to pretty print all top-level declarations of a language, but using hang for let expressions is fine.

align :: Functor m => m Doc -> m Doc Source #

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 laid out as:

  hi nice
world


hang :: Functor m => Int -> m Doc -> m Doc Source #

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 :: Functor m => Int -> m Doc -> m Doc Source #

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 :: Applicative m => m Doc -> m Doc -> m Doc -> m [Doc] -> m Doc Source #

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 laid out with a page width of 20 as:

  list [10,200,3000]


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

  list [10
,200
,3000]


list :: Functor m => m [Doc] -> m Doc Source #

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 :: Functor m => m [Doc] -> m Doc Source #

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 :: Functor m => m [Doc] -> m Doc Source #

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

(<+>) :: Applicative m => m Doc -> m Doc -> m Doc infixr 6 Source #

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

(<++>) :: Applicative m => m Doc -> m Doc -> m Doc infixr 6 Source #

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

(<$>) :: Applicative m => m Doc -> m Doc -> m Doc infixr 5 Source # The document (x <$> y) concatenates document x and y with a line in between. (infixr 5)

(</>) :: Applicative m => m Doc -> m Doc -> m Doc infixr 5 Source #

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)

(<$$>) :: Applicative m => m Doc -> m Doc -> m Doc infixr 5 Source # The document (x <$$> y) concatenates document x and y with a linebreak in between. (infixr 5)

(<//>) :: Applicative m => m Doc -> m Doc -> m 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 :: Functor m => m [Doc] -> m Doc Source #

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

vsep :: Functor m => m [Doc] -> m 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 laid 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 :: Functor m => m [Doc] -> m Doc Source # The document (fillSep xs) concatenates documents xs horizontally with (<+>) as long as its fits the page, then inserts a line and continues doing that for all documents in xs. fillSep xs = foldr (</>) empty xs sep :: Functor m => m [Doc] -> m 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 :: Functor m => m [Doc] -> m Doc Source #

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

vcat :: Functor m => m [Doc] -> m Doc Source #

The document (vcat xs) concatenates all documents xs vertically with (<$$>). If a group undoes the line breaks inserted by vcat, all documents are directly concatenated. fillCat :: Functor m => m [Doc] -> m Doc Source # The document (fillCat xs) concatenates documents xs horizontally with (<>) as long as its fits the page, then inserts a linebreak and continues doing that for all documents in xs. fillCat xs = foldr (<//>) empty xs cat :: Functor m => m [Doc] -> m Doc Source # The document (cat xs) concatenates all documents xs either horizontally with (<>), if it fits the page, or vertically with (<$$>).

cat xs = group (vcat xs)

punctuate :: Applicative m => m Doc -> m [Doc] -> m [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 laid out on a page width of 20 as:

  (words,in,a,tuple)


But when the page width is 15, it is laid 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 :: Functor m => Int -> m Doc -> m Doc Source #

The document (fill i x) renders document x. It then 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 laid out as:

  let empty  :: Doc
nest   :: Int -> Doc -> Doc
linebreak :: Doc


fillBreak :: Functor m => Int -> m Doc -> m Doc Source #

The document (fillBreak i x) first renders document x. It then 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 :: Applicative m => m Doc -> m Doc -> m Doc -> m Doc Source #

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

enclose l r x = l beside x beside r

squotes :: Functor m => m Doc -> m Doc Source #

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

dquotes :: Functor m => m Doc -> m Doc Source #

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

parens :: Functor m => m Doc -> m Doc Source #

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

angles :: Functor m => m Doc -> m Doc Source #

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

braces :: Functor m => m Doc -> m Doc Source #

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

brackets :: Functor m => m Doc -> m Doc Source #

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

# Character documents

lparen :: Applicative m => m Doc Source #

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

rparen :: Applicative m => m Doc Source #

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

langle :: Applicative m => m Doc Source #

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

rangle :: Applicative m => m Doc Source #

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

lbrace :: Applicative m => m Doc Source #

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

rbrace :: Applicative m => m Doc Source #

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

lbracket :: Applicative m => m Doc Source #

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

rbracket :: Applicative m => m Doc Source #

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

squote :: Applicative m => m Doc Source #

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

dquote :: Applicative m => m Doc Source #

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

semi :: Applicative m => m Doc Source #

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

colon :: Applicative m => m Doc Source #

The document colon contains a colon, ":".

comma :: Applicative m => m Doc Source #

The document comma contains a comma, ",".

space :: Applicative m => m Doc Source #

The document space contains a single space, " ".

x <+> y = x beside space beside y

dot :: Applicative m => m Doc Source #

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

backslash :: Applicative m => m Doc Source #

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

equals :: Applicative m => m Doc Source #

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

# Primitive type documents

string :: Applicative m => Text -> m Doc Source #

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 :: Applicative m => Int -> m Doc Source #

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

integer :: Applicative m => Integer -> m Doc Source #

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

float :: Applicative m => Float -> m Doc Source #

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

double :: Applicative m => Double -> m Doc Source #

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

rational :: Applicative m => Rational -> m Doc Source #

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

bool :: Applicative m => Bool -> m Doc Source #

The document (bool b) shows the literal boolean b using text.

# Position-based combinators

column :: Functor m => m (Int -> Doc) -> m Doc Source #

Specifies how to create the document based upon which column it is in.

nesting :: Functor m => m (Int -> Doc) -> m Doc Source #

Specifies how to nest the document based upon which column it is being nested in.

width :: Applicative m => m Doc -> m (Int -> Doc) -> m Doc Source #

# 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 # MethodsprettyList :: [Bool] -> Doc Source # Source # MethodsprettyList :: [Char] -> Doc Source # Source # MethodsprettyList :: [Double] -> Doc Source # Source # MethodsprettyList :: [Float] -> Doc Source # Source # MethodsprettyList :: [Int] -> Doc Source # Source # MethodsprettyList :: [Integer] -> Doc Source # Pretty () Source # Methodspretty :: () -> Doc Source #prettyList :: [()] -> Doc Source # Source # MethodsprettyList :: [Text] -> Doc Source # Source # MethodsprettyList :: [Text] -> Doc Source # Source # MethodsprettyList :: [Doc] -> Doc Source # Pretty a => Pretty [a] Source # Methodspretty :: [a] -> Doc Source #prettyList :: [[a]] -> Doc Source # Pretty a => Pretty (Maybe a) Source # Methodspretty :: Maybe a -> Doc Source #prettyList :: [Maybe a] -> Doc Source # (Pretty a, Pretty b) => Pretty (a, b) Source # Methodspretty :: (a, b) -> Doc Source #prettyList :: [(a, b)] -> Doc Source # (Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) Source # Methodspretty :: (a, b, c) -> Doc Source #prettyList :: [(a, b, c)] -> Doc Source #

prettyM :: (Pretty a, Applicative m) => a -> m Doc Source #

A monadic version of pretty; this is to allow you to use the Pretty class without having to create extra instances. Alternatively, you may wish to make a variant of Pretty using the actual Monad to be used.

# Rendering

data SimpleDoc Source #

The data type SimpleDoc 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 to your own output format.

Constructors

 SEmpty SChar Char SimpleDoc SText !Int64 Builder SimpleDoc SLine !Int64 SimpleDoc

Instances

 Source # MethodsshowList :: [SimpleDoc] -> ShowS #

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.

(renderOneLine x) renders document x without adding any indentation or newlines.

(displayB simpleDoc) takes the output simpleDoc from a rendering function and transforms it to a Builder type (for further manipulation before converting to a lazy Text).

(displayT simpleDoc) takes the output simpleDoc from a rendering function and transforms it to a lazy Text value.

showWidth :: Int -> Doc -> Text
showWidth w x = displayT (renderPretty 0.4 w x)

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

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

putDoc :: Doc -> 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 -> 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'
['T.pack' "vertical", 'T.pack' "text"]))
'hClose' handle`