Text.PrettyPrint.Mainland

This module is based on A Prettier Printer by Phil Wadler in The Fun of Programming, Jeremy Gibbons and Oege de Moor (eds) http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf

At the time it was originally written I didn't know about Daan Leijen's pretty printing module based on the same paper. I have since incorporated many of his improvements. This module is geared towards pretty printing source code; its main advantages over other libraries are the ability to automatically track the source locations associated with pretty printed values and output appropriate #line pragmas and the use of Text for output.

The document type

data Doc

The abstract type of documents.

Instances

IsString Doc

Defined in Text.PrettyPrint.Mainland

Methods

fromString :: String -> Doc

Semigroup Doc

Defined in Text.PrettyPrint.Mainland

Methods

(<>) :: Doc -> Doc -> Doc

sconcat :: NonEmpty Doc -> Doc

stimes :: Integral b => b -> Doc -> Doc

Monoid Doc

Defined in Text.PrettyPrint.Mainland

Methods

mempty :: Doc

mappend :: Doc -> Doc -> Doc

mconcat :: [Doc] -> Doc

Pretty Doc

Defined in Text.PrettyPrint.Mainland.Class

Methods

ppr :: Doc -> Doc

pprPrec :: Int -> Doc -> Doc

pprList :: [Doc] -> Doc

Constructing documents

Converting values into documents

text :: String -> Doc

The document text s consists of the string s, which should not contain any newlines. For a string that may include newlines, use string.

bool :: Bool -> Doc

The document bool b is equivalent to text (show b).

char :: Char -> Doc

The document char c consists the single character c.

string :: String -> Doc

The document string s consists of all the characters in s but with newlines replaced by line.

int :: Int -> Doc

The document int i is equivalent to text (show i).

integer :: Integer -> Doc

The document integer i is equivalent to text (show i). text.

float :: Float -> Doc

The document float f is equivalent to text (show f).

double :: Double -> Doc

The document double d is equivalent to text (show d).

rational :: Rational -> Doc

The document rational r is equivalent to text (show r).

strictText :: Text -> Doc

The document strictText s consists of the Text s, which should not contain any newlines.

lazyText :: Text -> Doc

The document lazyText s consists of the Text s, which should not contain any newlines.

Simple documents documents

star :: Doc

The document star consists of an asterisk, "*".

colon :: Doc

The document colon consists of a colon, ":".

comma :: Doc

The document comma consists of a comma, ",".

dot :: Doc

The document dot consists of a period, ".".

equals :: Doc

The document equals consists of an equals sign, "=".

semi :: Doc

The document semi consists of a semicolon, ";".

space :: Doc

The document space consists of a space, " ".

spaces :: Int -> Doc

The document space n consists of n spaces.

backquote :: Doc

The document backquote consists of a backquote, "`".

squote :: Doc

The document squote consists of a single quote, "\'".

dquote :: Doc

The document dquote consists of a double quote, "\"".

langle :: Doc

The document langle consists of a less-than sign, "<".

rangle :: Doc

The document rangle consists of a greater-than sign, ">".

lbrace :: Doc

The document lbrace consists of a left brace, "{".

rbrace :: Doc

The document rbrace consists of a right brace, "}".

lbracket :: Doc

The document lbracket consists of a right brace, "[".

rbracket :: Doc

The document rbracket consists of a right brace, "]".

lparen :: Doc

The document lparen consists of a right brace, "(".

rparen :: Doc

The document rparen consists of a right brace, ")".

Basic document combinators

empty :: Doc

The empty document.

srcloc :: Located a => a -> Doc

The document srcloc x tags the current line with locOf x. Only shown when running prettyPragma and friends.

line :: Doc

The document line advances to the next line and indents to the current indentation level. When undone by group, it behaves like space.

softline :: Doc

Becomes space if there is room, otherwise line.

pretty 11 $ text "foo" <+/> text "bar" <+/> text "baz" =="foo bar baz"
pretty  7 $ text "foo" <+/> text "bar" <+/> text "baz" == "foo bar\nbaz"
pretty  6 $ text "foo" <+/> text "bar" <+/> text "baz" == "foo\nbar\nbaz"

softbreak :: Doc

Becomes empty if there is room, otherwise line.

(<|>) :: Doc -> Doc -> Doc infixl 3

Provide alternative layouts of the same content. Invariant: both arguments must flatten to the same document.

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

Concatenates two documents with a space in between, with identity empty.

(</>) :: Doc -> Doc -> Doc infixr 5

Concatenates two documents with a line in between, with identity empty.

(<+/>) :: Doc -> Doc -> Doc infixr 5

Concatenates two documents with a softline in between, with identity empty.

(<//>) :: Doc -> Doc -> Doc infixr 5

Concatenates two documents with a softbreak in between.

group :: Doc -> Doc

The document group d will flatten d to one line if there is room for it, otherwise the original d.

flatten :: Doc -> Doc

The document flatten d will flatten d to one line.

Wrapping documents in delimiters

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

The document enclose l r d encloses the document d between the documents l and r using <>. It obeys the law

enclose l r d = l <> d <> r

squotes :: Doc -> Doc

The document squotes d encloses the alinged document d in '...'.

dquotes :: Doc -> Doc

The document dquotes d encloses the aligned document d in "...".

angles :: Doc -> Doc

The document angles d encloses the aligned document d in <...>.

backquotes :: Doc -> Doc

The document backquotes d encloses the aligned document d in `...`.

braces :: Doc -> Doc

The document braces d encloses the aligned document d in {...}.

brackets :: Doc -> Doc

The document brackets d encloses the aligned document d in [...].

parens :: Doc -> Doc

The document parens d encloses the aligned document d in (...).

parensIf :: Bool -> Doc -> Doc

The document parensIf p d encloses the document d in parenthesis if p is True, and otherwise yields just d.

Combining lists of documents

folddoc :: (Doc -> Doc -> Doc) -> [Doc] -> Doc

The document folddoc f ds obeys the laws:

• folddoc f [] = empty

• folddoc f [d1, d2, ..., dnm1, dn] = d1 f (d2 f ... (dnm1 f dn))

spread :: [Doc] -> Doc

The document spread ds concatenates the documents ds with space.

stack :: [Doc] -> Doc

The document stack ds concatenates the documents ds with line.

cat :: [Doc] -> Doc

The document cat ds concatenates the documents ds with the empty document as long as there is room, and uses line when there isn't.

sep :: [Doc] -> Doc

The document sep ds concatenates the documents ds with the space document as long as there is room, and uses line when there isn't.

punctuate :: Doc -> [Doc] -> [Doc]

The document punctuate p ds obeys the law:

punctuate p [d1, d2, ..., dn] = [d1 <> p, d2 <> p, ..., dn]

commasep :: [Doc] -> Doc

The document commasep ds comma-space separates ds, aligning the resulting document to the current nesting level.

semisep :: [Doc] -> Doc

The document semisep ds semicolon-space separates ds, aligning the resulting document to the current nesting level.

enclosesep :: Doc -> Doc -> Doc -> [Doc] -> Doc

The document enclosesep l r p ds separates ds with the punctuation p and encloses the result using l and r. When wrapped, punctuation appears at the end of the line. The enclosed portion of the document is aligned one column to the right of the opening document.

> ws = map text (words "The quick brown fox jumps over the lazy dog")
> test = pretty 15 (enclosesep lparen rparen comma ws)

will be layed out as:

(The, quick,
 brown, fox,
 jumps, over,
 the, lazy,
 dog)

tuple :: [Doc] -> Doc

The document tuple ds separates ds with commas and encloses them with parentheses.

list :: [Doc] -> Doc

The document list ds separates ds with commas and encloses them with brackets.

Alignment and indentation

align :: Doc -> Doc

The document align d renders d with a nesting level set to the current column.

hang :: Int -> Doc -> Doc

The document hang i d renders d with a nesting level set to the current column plus i, not including the first line.

indent :: Int -> Doc -> Doc

The document indent i d renders d with a nesting level set to the current column plus i, including the first line.

nest :: Int -> Doc -> Doc

The document nest i d renders the document d with the current indentation level increased by i.

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

The document column f is produced by calling f with the current column.

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

The document column f is produced by calling f with the current nesting level.

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

The document width d f is produced by concatenating d with the result of calling f with the width of the document d.

fill :: Int -> Doc -> Doc

The document fill i d renders document x, appending spaces until the width is equal to i. If the width of d is already greater than i, nothing is appended.

fillbreak :: Int -> Doc -> Doc

The document fillbreak i d renders document d, appending spaces until the width is equal to i. If the width of d is already greater than i, the nesting level is increased by i and a line is appended.

Utilities

faildoc :: Monad m => Doc -> m a

Equivalent of fail, but with a document instead of a string.

errordoc :: Doc -> a

Equivalent of error, but with a document instead of a string.

The rendered document type

data RDoc

A rendered document.

Constructors

REmpty

The empty document

RChar !Char RDoc

A single character

RString !Int String RDoc

Doc with associated length (to avoid recomputation)

RText Text RDoc

Text

RLazyText Text RDoc

Text

RPos Pos RDoc

Tag output with source location

RLine !Int RDoc

A newline with the indentation of the subsequent line. If this is followed by a RPos, output an appropriate #line pragma before the newline.

Document rendering

render :: Int -> Doc -> RDoc

Render a document given a maximum width.

renderCompact :: Doc -> RDoc

Render a document without indentation on infinitely long lines. Since no 'pretty' printing is involved, this renderer is fast. The resulting output contains fewer characters.

displayS :: RDoc -> ShowS

Display a rendered document.

prettyS :: Int -> Doc -> ShowS

Render and display a document.

pretty :: Int -> Doc -> String

Render and convert a document to a Doc.

prettyCompactS :: Doc -> ShowS

Render and display a document compactly.

prettyCompact :: Doc -> String

Render and convert a document to a Doc compactly.

displayPragmaS :: RDoc -> ShowS

Display a rendered document with #line pragmas.

prettyPragmaS :: Int -> Doc -> ShowS

Render and display a document with #line pragmas.

prettyPragma :: Int -> Doc -> String

Render and convert a document to a Doc with #line pragmas.

> let loc = Loc (Pos "filename" 3 5 7) (Pos "filename" 5 7 9)
> in  putStrLn $ prettyPragma 80 $ srcloc loc <> text "foo" </> text "bar" </> text "baz"

will be printed as

foo
#line 3 "filename"
bar
baz

displayLazyText :: RDoc -> Text

Display a rendered document as Text. Uses a builder.

prettyLazyText :: Int -> Doc -> Text

Render and display a document as Text. Uses a builder.

displayPragmaLazyText :: RDoc -> Text

Display a rendered document with #line pragmas as Text. Uses a builder.

prettyPragmaLazyText :: Int -> Doc -> Text

Render and convert a document to Text with #line pragmas. Uses a builder.

Document output

putDoc :: Doc -> IO ()

Render a document with a width of 80 and print it to standard output.

putDocLn :: Doc -> IO ()

Render a document with a width of 80 and print it to standard output, followed by a newline.

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

Render a document with a width of 80 and print it to the specified handle.

hPutDocLn :: Handle -> Doc -> IO ()

Render a document with a width of 80 and print it to the specified handle, followed by a newline.