Text.PrettyPrint.Leijen

list :: Array Doc -> Doc

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 :: Array Doc -> Doc

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 :: Array Doc -> Doc

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

encloseSep :: Doc -> Doc -> Doc -> Array Doc -> Doc

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] @

punctuate :: Doc -> Array Doc -> Array Doc

@(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'.)

sep :: Array Doc -> Doc

The document @(sep xs)@ concatenates all documents @xs@ either horizontally with @(<+>)@, if it fits the page, or vertically with @(<$>)@.

sep xs = group (vsep xs)

foldr1 :: forall a. Monoid a => (a -> a -> a) -> Array a -> a

fillSep :: Array Doc -> Doc

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

hsep :: Array Doc -> Doc

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

vsep :: Array Doc -> Doc

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 @

cat :: Array Doc -> Doc

The document @(cat xs)@ concatenates all documents @xs@ either horizontally with @(<>)@, if it fits the page, or vertically with @(<$$>)@.

cat xs = group (vcat xs)

fillCat :: Array Doc -> Doc

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 = foldr1 (<//>) empty

hcat :: Array Doc -> Doc

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

vcat :: Array Doc -> Doc

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.

appendWithSpace :: Doc -> Doc -> Doc

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

Operator alias for Text.PrettyPrint.Leijen.appendWithSpace (right-associative / precedence 6)

appendWithSoftline :: Doc -> Doc -> Doc

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)

Operator alias for Text.PrettyPrint.Leijen.appendWithSoftline (right-associative / precedence 5)

appendWithSoftbreak :: Doc -> Doc -> Doc

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)

Operator alias for Text.PrettyPrint.Leijen.appendWithSoftbreak (right-associative / precedence 5)

appendWithLine :: Doc -> Doc -> Doc

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

Operator alias for Text.PrettyPrint.Leijen.appendWithLine (right-associative / precedence 5)

appendWithLinebreak :: Doc -> Doc -> Doc

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

Operator alias for Text.PrettyPrint.Leijen.appendWithLinebreak (right-associative / precedence 5)

softline :: Doc

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

softline = group line

softbreak :: Doc

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

softbreak = group linebreak

squotes :: Doc -> Doc

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

dquotes :: Doc -> Doc

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

braces :: Doc -> Doc

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

parens :: Doc -> Doc

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

angles :: Doc -> Doc

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

brackets :: Doc -> Doc

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

enclose :: Doc -> Doc -> Doc -> Doc

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

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

lparen :: Doc

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

rparen :: Doc

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

langle :: Doc

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

rangle :: Doc

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

lbrace :: Doc

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

rbrace :: Doc

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

lbracket :: Doc

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

rbracket :: Doc

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

squote :: Doc

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

dquote :: Doc

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

semi :: Doc

The document @semi@ contains a semicolon, ";".

colon :: Doc

The document @colon@ contains a colon, ":".

comma :: Doc

The document @comma@ contains a comma, ",".

space :: Doc

The document @space@ contains a single space, " ".

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

dot :: Doc

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

backslash :: Doc

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

equals :: Doc

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

string :: String -> Doc

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.

bool :: Boolean -> Doc

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

int :: Int -> Doc

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

number :: Number -> Doc

The document @(number f)@ shows the literal number @f@ using 'text'.

fillBreak :: Int -> Doc -> Doc

The document @(fillBreak i x)@ first renders document @x@. It than appends @space@s 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 @

fill :: Int -> Doc -> Doc

The document @(fill i x)@ renders document @x@. It than appends @space@s 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 @

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

indent :: Int -> Doc -> Doc

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 ! @

hang :: Int -> Doc -> Doc

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)

align :: Doc -> Doc

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 @

data Doc

The abstract data type @Doc@ represents pretty documents.

More specifically, a value of type @Doc@ represents a non-empty set of possible renderings of a document. The rendering functions select one of these possibilities.

@Doc@ is an instance of the 'Show' class. @(show doc)@ pretty prints document @doc@ with a page width of 80 characters and a ribbon width of 32 characters.

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

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

@ hello world @

Constructors

• Fail
• Empty
• Char Char
• Text Int String
• Line
• FlatAlt Doc Doc
• Cat Doc Doc
• Nest Int Doc
• Union Doc Doc
• Column (Int -> Doc)
• Columns (Maybe Int -> Doc)
• Nesting (Int -> Doc)

Instances

• Semigroup Doc
• Monoid Doc
• Show Doc

data SimpleDoc

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

Instances

• Eq SimpleDoc
• Ord SimpleDoc
• Generic SimpleDoc _
• Show SimpleDoc

data LazySimpleDoc

Constructors

• SFail'
• SEmpty'
• SChar' Char (Lazy LazySimpleDoc)
• SText' Int String (Lazy LazySimpleDoc)
• SLine' Int (Lazy LazySimpleDoc)

forceSimpleDoc :: LazySimpleDoc -> SimpleDoc

empty :: Doc

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

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

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.

line :: Doc

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'.

linebreak :: Doc

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'.

hardline :: Doc

A linebreak that will never be flattened; it is guaranteed to render as a newline.

beside :: Doc -> Doc -> Doc

nest :: Int -> Doc -> Doc

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 ! @

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

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

columns :: (Maybe Int -> Doc) -> Doc

group :: Doc -> Doc

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.

flatAlt :: Doc -> Doc -> Doc

A document that is normally rendered as the first argument, but when flattened, is rendered as the second document.

flatten :: Doc -> Doc

data Docs

list of indentation/document pairs; saves an indirection over [(Int,Doc)]

Constructors

• Nil
• Cons Int Doc Docs

renderPretty :: Number -> Int -> Doc -> 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.

renderSmart :: Number -> Int -> Doc -> SimpleDoc

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.

renderFits :: (Int -> Int -> Int -> LazySimpleDoc -> Boolean) -> Number -> Int -> Doc -> SimpleDoc

fits1 :: Int -> Int -> Int -> LazySimpleDoc -> Boolean

@fits1@ does 1 line lookahead.

fitsR :: Int -> Int -> Int -> LazySimpleDoc -> Boolean

@fitsR@ has a little more lookahead: assuming that nesting roughly corresponds to syntactic depth, @fitsR@ checks that not only the current line fits, but the entire syntactic structure being formatted at this level of indentation fits. If we were to remove the second case for @SLine@, we would check that not only the current structure fits, but also the rest of the document, which would be slightly more intelligent but would have exponential runtime (and is prohibitively expensive in practice). p = pagewidth m = minimum nesting level to fit in w = the width in which to fit the first line

renderCompact :: Doc -> SimpleDoc

@(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.

displayS :: SimpleDoc -> String

@(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.

spaces :: Int -> String

indentation :: Int -> String