Prettyprinter

Overview

This module defines a prettyprinter to format text in a flexible and convenient way. The idea is to combine a Document out of many small components, then using a layouter to convert it to an easily renderable SimpleDocStream, which can then be rendered to a variety of formats, for example plain Text.

The documentation consists of several parts:

1. Just below is some general information about the library.
2. The actual library with extensive documentation and examples
3. Migration guide for users familiar with (ansi-)wl-pprint

Starting out

As a reading list for starters, some of the most commonly used functions in this module include <>, hsep, <+>, vsep, align, hang. These cover many use cases already, and many other functions are variations or combinations of these.

Simple example

Let’s prettyprint a simple Haskell type definition. First, intersperse -> and add a leading ::,

>>> let prettyType = align . sep . zipWith (<+>) ("::" : repeat "->")

The sep function is one way of concatenating documents, there are multiple others, e.g. vsep, cat and fillSep. In our case, sep space-separates all entries if there is space, and newlines if the remaining line is too short.

Second, prepend the name to the type,

>>> let prettyDecl n tys = pretty n <+> prettyType tys

Now we can define a document that contains some type signature:

>>> let doc = prettyDecl "example" ["Int", "Bool", "Char", "IO ()"]

This document can now be printed, and it automatically adapts to available space. If the page is wide enough (80 characters in this case), the definitions are space-separated,

>>> putDocW 80 doc
example :: Int -> Bool -> Char -> IO ()

If we narrow the page width to only 20 characters, the same document renders vertically aligned:

>>> putDocW 20 doc
example :: Int
        -> Bool
        -> Char
        -> IO ()

Speaking of alignment, had we not used align, the -> would be at the beginning of each line, and not beneath the ::.

The putDocW renderer used here is from Prettyprinter.Util.

General workflow

╔══════════╗
║          ║                         ╭────────────────────╮
║          ║                         │ vsep, pretty, <+>, │
║          ║                         │ nest, align, …     │
║          ║                         ╰─────────┬──────────╯
║          ║                                   │
║  Create  ║                                   │
║          ║                                   │
║          ║                                   ▽
║          ║                         ╭───────────────────╮
║          ║                         │        Doc        │
╠══════════╣                         │  (rich document)  │
║          ║                         ╰─────────┬─────────╯
║          ║                                   │
║          ║                                   │ Layout algorithms
║  Layout  ║                                   │ e.g. layoutPretty
║          ║                                   ▽
║          ║                         ╭───────────────────╮
║          ║                         │  SimpleDocStream  │
╠══════════╣                         │ (simple document) │
║          ║                         ╰─────────┬─────────╯
║          ║                                   │
║          ║                                   ├─────────────────────────────╮
║          ║                                   │                             │ treeForm
║          ║                                   │                             ▽
║          ║                                   │                     ╭───────────────╮
║          ║                                   │                     │ SimpleDocTree │
║  Render  ║                                   │                     ╰───────┬───────╯
║          ║                                   │                             │
║          ║               ╭───────────────────┼─────────────────╮  ╭────────┴────────╮
║          ║               │                   │                 │  │                 │
║          ║               ▽                   ▽                 ▽  ▽                 ▽
║          ║       ╭───────────────╮   ╭───────────────╮   ╭───────────────╮   ╭───────────────╮
║          ║       │ ANSI terminal │   │  Plain Text   │   │ other/custom  │   │     HTML      │
║          ║       ╰───────────────╯   ╰───────────────╯   ╰───────────────╯   ╰───────────────╯
║          ║
╚══════════╝

How the layout works

There are two key concepts to laying a document out: the available width, and grouping.

Available width

The page has a certain maximum width, which the layouter tries to not exceed, by inserting line breaks where possible. The functions given in this module make it fairly straightforward to specify where, and under what circumstances, such a line break may be inserted by the layouter, for example via the sep function.

There is also the concept of ribbon width. The ribbon is the part of a line that is printed, i.e. the line length without the leading indentation. The layouters take a ribbon fraction argument, which specifies how much of a line should be filled before trying to break it up. A ribbon width of 0.5 in a document of width 80 will result in the layouter to try to not exceed 0.5*80 = 40 (ignoring current indentation depth).

Grouping

A document can be grouped, which tells the layouter that it should attempt to collapse it to a single line. If the result does not fit within the constraints (given by page and ribbon widths), the document is rendered unaltered. This allows fallback definitions, so that we get nice results even when the original document would exceed the layout constraints.

Things the prettyprinter cannot do

Due to how the Wadler/Leijen algorithm is designed, a couple of things are unsupported right now, with a high possibility of having no sensible implementation without significantly changing the layout algorithm. In particular, this includes

• Leading symbols instead of just spaces for indentation, as used by the Linux tree tool for example
• Multi-column layouts, in particular tables with multiple cells of equal width adjacent to each other

Some helpful tips

Which kind of annotation should I use?

Summary: Use semantic annotations for Doc, and after layouting map to backend-specific ones.

For example, suppose you want to prettyprint some programming language code. If you want keywords to be red, you should annotate the Doc with a type that has a Keyword field (without any notion of color), and then after layouting convert the annotations to map Keyword to e.g. Red (using reAnnotateS). The alternative that I do not recommend is directly annotating the Doc with Red.

While both versions would superficially work equally well and would create identical output, the recommended way has two significant advantages: modularity and extensibility.

Modularity: To change the color of keywords later, you have to touch one point, namely the mapping in reAnnotateS, where Keyword is mapped to Red. If you have 'annotate Red …' everywher, you’ll have to do a full text replacement, producing a large diff and touching lots of places for a very small change.

Extensibility: Adding a different backend in the recommended version is simply adding another reAnnotateS to convert the Doc annotation to something else. On the other hand, if you have Red as an annotation in the Doc already and the other backend does not support anything red (think of plain text or a website where red doesn’t work well with the rest of the style), you’ll have to worry about what to map »redness« to, which has no canonical answer. Should it be omitted? What does »red« mean anyway – maybe keywords and variables are red, and you want to change only the color of variables?

Documents

data Doc ann

The abstract data type Doc ann represents pretty documents that have been annotated with data of type ann.

More specifically, a value of type Doc represents a non-empty set of possible layouts of a document. The layout functions select one of these possibilities, taking into account things like the width of the output document.

The annotation is an arbitrary piece of data associated with (part of) a document. Annotations may be used by the rendering backends in order to display output differently, such as

• color information (e.g. when rendering to the terminal)
• mouseover text (e.g. when rendering to rich HTML)
• whether to show something or not (to allow simple or detailed versions)

The simplest way to display a Doc is via the Show class.

>>> putStrLn (show (vsep ["hello", "world"]))
hello
world

Instances

Functor Doc

Alter the document’s annotations.

This instance makes Doc more flexible (because it can be used in Functor-polymorphic values), but fmap is much less readable compared to using reAnnotate in code that only works for Doc anyway. Consider using the latter when the type does not matter.

Defined in Prettyprinter.Internal

Methods

fmap :: (a -> b) -> Doc a -> Doc b

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

Show (Doc ann)

(show doc) prettyprints document doc with defaultLayoutOptions, ignoring all annotations.

Defined in Prettyprinter.Internal

Methods

showsPrec :: Int -> Doc ann -> ShowS

show :: Doc ann -> String

showList :: [Doc ann] -> ShowS

IsString (Doc ann)

>>> pretty ("hello\nworld")
hello
world

This instance uses the Pretty Doc instance, and uses the same newline to line conversion.

Defined in Prettyprinter.Internal

Methods

fromString :: String -> Doc ann

Generic (Doc ann)

Defined in Prettyprinter.Internal

Associated Types

type Rep (Doc ann) :: Type -> Type

Methods

from :: Doc ann -> Rep (Doc ann) x

to :: Rep (Doc ann) x -> Doc ann

Semigroup (Doc ann)

x <> y = hcat [x, y]

>>> "hello" <> "world" :: Doc ann
helloworld

Defined in Prettyprinter.Internal

Methods

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

sconcat :: NonEmpty (Doc ann) -> Doc ann

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

Monoid (Doc ann)

mempty = emptyDoc
mconcat = hcat

>>> mappend "hello" "world" :: Doc ann
helloworld

Defined in Prettyprinter.Internal

Methods

mempty :: Doc ann

mappend :: Doc ann -> Doc ann -> Doc ann

mconcat :: [Doc ann] -> Doc ann

type Rep (Doc ann)

Defined in Prettyprinter.Internal

type Rep (Doc ann) = D1 (MetaData "Doc" "Prettyprinter.Internal" "prettyprinter-1.7.0-3a58dVee6cSUUePu4NnX6" False) (((C1 (MetaCons "Fail" PrefixI False) (U1 :: Type -> Type) :+: (C1 (MetaCons "Empty" PrefixI False) (U1 :: Type -> Type) :+: C1 (MetaCons "Char" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Char)))) :+: (C1 (MetaCons "Text" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Int) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Text)) :+: (C1 (MetaCons "Line" PrefixI False) (U1 :: Type -> Type) :+: C1 (MetaCons "FlatAlt" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann)) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann)))))) :+: ((C1 (MetaCons "Cat" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann)) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann))) :+: (C1 (MetaCons "Nest" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Int) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann))) :+: C1 (MetaCons "Union" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann)) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann))))) :+: ((C1 (MetaCons "Column" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Int -> Doc ann))) :+: C1 (MetaCons "WithPageWidth" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (PageWidth -> Doc ann)))) :+: (C1 (MetaCons "Nesting" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Int -> Doc ann))) :+: C1 (MetaCons "Annotated" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 ann) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Doc ann)))))))

Basic functionality

class Pretty a where

Overloaded conversion to Doc.

Laws:

1. output should be pretty. :-)

Minimal complete definition

pretty

Methods

pretty :: a -> Doc ann

>>> pretty 1 <+> pretty "hello" <+> pretty 1.234
1 hello 1.234

pretty :: Show a => a -> Doc ann

>>> pretty 1 <+> pretty "hello" <+> pretty 1.234
1 hello 1.234

prettyList :: [a] -> Doc ann

prettyList is only used to define the instance Pretty a => Pretty [a]. In normal circumstances only the pretty function is used.

>>> prettyList [1, 23, 456]
[1, 23, 456]

Instances

Pretty Bool

>>> pretty True
True

Defined in Prettyprinter.Internal

Methods

pretty :: Bool -> Doc ann

prettyList :: [Bool] -> Doc ann

Pretty Char

Instead of (pretty '\n'), consider using line as a more readable alternative.

>>> pretty 'f' <> pretty 'o' <> pretty 'o'
foo
>>> pretty ("string" :: String)
string

Defined in Prettyprinter.Internal

Methods

pretty :: Char -> Doc ann

prettyList :: [Char] -> Doc ann

Pretty Double

>>> pretty (exp 1 :: Double)
2.71828182845904...

Defined in Prettyprinter.Internal

Methods

pretty :: Double -> Doc ann

prettyList :: [Double] -> Doc ann

Pretty Float

>>> pretty (pi :: Float)
3.1415927

Defined in Prettyprinter.Internal

Methods

pretty :: Float -> Doc ann

prettyList :: [Float] -> Doc ann

Pretty Int

>>> pretty (123 :: Int)
123

Defined in Prettyprinter.Internal

Methods

pretty :: Int -> Doc ann

prettyList :: [Int] -> Doc ann

Pretty Int8

Defined in Prettyprinter.Internal

Methods

pretty :: Int8 -> Doc ann

prettyList :: [Int8] -> Doc ann

Pretty Int16

Defined in Prettyprinter.Internal

Methods

pretty :: Int16 -> Doc ann

prettyList :: [Int16] -> Doc ann

Pretty Int32

Defined in Prettyprinter.Internal

Methods

pretty :: Int32 -> Doc ann

prettyList :: [Int32] -> Doc ann

Pretty Int64

Defined in Prettyprinter.Internal

Methods

pretty :: Int64 -> Doc ann

prettyList :: [Int64] -> Doc ann

Pretty Integer

>>> pretty (2^123 :: Integer)
10633823966279326983230456482242756608

Defined in Prettyprinter.Internal

Methods

pretty :: Integer -> Doc ann

prettyList :: [Integer] -> Doc ann

Pretty Natural

Defined in Prettyprinter.Internal

Methods

pretty :: Natural -> Doc ann

prettyList :: [Natural] -> Doc ann

Pretty Word

Defined in Prettyprinter.Internal

Methods

pretty :: Word -> Doc ann

prettyList :: [Word] -> Doc ann

Pretty Word8

Defined in Prettyprinter.Internal

Methods

pretty :: Word8 -> Doc ann

prettyList :: [Word8] -> Doc ann

Pretty Word16

Defined in Prettyprinter.Internal

Methods

pretty :: Word16 -> Doc ann

prettyList :: [Word16] -> Doc ann

Pretty Word32

Defined in Prettyprinter.Internal

Methods

pretty :: Word32 -> Doc ann

prettyList :: [Word32] -> Doc ann

Pretty Word64

Defined in Prettyprinter.Internal

Methods

pretty :: Word64 -> Doc ann

prettyList :: [Word64] -> Doc ann

Pretty ()

>>> pretty ()
()

The argument is not used,

>>> pretty (error "Strict?" :: ())
()

Defined in Prettyprinter.Internal

Methods

pretty :: () -> Doc ann

prettyList :: [()] -> Doc ann

Pretty Void

Finding a good example for printing something that does not exist is hard, so here is an example of printing a list full of nothing.

>>> pretty ([] :: [Void])
[]

Defined in Prettyprinter.Internal

Methods

pretty :: Void -> Doc ann

prettyList :: [Void] -> Doc ann

Pretty Text

(lazy Doc instance, identical to the strict version)

Defined in Prettyprinter.Internal

Methods

pretty :: Text -> Doc ann

prettyList :: [Text] -> Doc ann

Pretty Text

Automatically converts all newlines to line.

>>> pretty ("hello\nworld" :: Text)
hello
world

Note that line can be undone by group:

>>> group (pretty ("hello\nworld" :: Text))
hello world

Manually use hardline if you definitely want newlines.

Defined in Prettyprinter.Internal

Methods

pretty :: Text -> Doc ann

prettyList :: [Text] -> Doc ann

Pretty a => Pretty [a]

>>> pretty [1,2,3]
[1, 2, 3]

Defined in Prettyprinter.Internal

Methods

pretty :: [a] -> Doc ann

prettyList :: [[a]] -> Doc ann

Pretty a => Pretty (Maybe a)

Ignore Nothings, print Just contents.

>>> pretty (Just True)
True
>>> braces (pretty (Nothing :: Maybe Bool))
{}

>>> pretty [Just 1, Nothing, Just 3, Nothing]
[1, 3]

Defined in Prettyprinter.Internal

Methods

pretty :: Maybe a -> Doc ann

prettyList :: [Maybe a] -> Doc ann

Pretty a => Pretty (Identity a)

>>> pretty (Identity 1)
1

Defined in Prettyprinter.Internal

Methods

pretty :: Identity a -> Doc ann

prettyList :: [Identity a] -> Doc ann

Pretty a => Pretty (NonEmpty a)

Defined in Prettyprinter.Internal

Methods

pretty :: NonEmpty a -> Doc ann

prettyList :: [NonEmpty a] -> Doc ann

(Pretty a1, Pretty a2) => Pretty (a1, a2)

>>> pretty (123, "hello")
(123, hello)

Defined in Prettyprinter.Internal

Methods

pretty :: (a1, a2) -> Doc ann

prettyList :: [(a1, a2)] -> Doc ann

(Pretty a1, Pretty a2, Pretty a3) => Pretty (a1, a2, a3)

>>> pretty (123, "hello", False)
(123, hello, False)

Defined in Prettyprinter.Internal

Methods

pretty :: (a1, a2, a3) -> Doc ann

prettyList :: [(a1, a2, a3)] -> Doc ann

Pretty a => Pretty (Const a b)

Defined in Prettyprinter.Internal

Methods

pretty :: Const a b -> Doc ann

prettyList :: [Const a b] -> Doc ann

viaShow :: Show a => a -> Doc ann

Convenience function to convert a Showable value to a Doc. If the String does not contain newlines, consider using the more performant unsafeViaShow.

unsafeViaShow :: Show a => a -> Doc ann

Convenience function to convert a Showable value /that must not contain newlines/ to a Doc. If there may be newlines, use viaShow instead.

emptyDoc :: Doc ann

The empty document behaves like (pretty ""), so it has a height of 1. This may lead to surprising behaviour if we expect it to bear no weight inside e.g. vcat, where we get an empty line of output from it (parens for visibility only):

>>> vsep ["hello", parens emptyDoc, "world"]
hello
()
world

Together with <>, emptyDoc forms the Monoid Doc.

nest

Arguments

:: Int

Change of nesting level

-> Doc ann

-> Doc ann

(nest i x) lays out the document x with the current nesting level (indentation of the following lines) increased by i. Negative values are allowed, and decrease the nesting level accordingly.

>>> vsep [nest 4 (vsep ["lorem", "ipsum", "dolor"]), "sit", "amet"]
lorem
    ipsum
    dolor
sit
amet

See also

• hang (nest relative to current cursor position instead of current nesting level)
• align (set nesting level to current cursor position)
• indent (increase indentation on the spot, padding with spaces).

line :: Doc ann

The line document advances to the next line and indents to the current nesting level.

>>> let doc = "lorem ipsum" <> line <> "dolor sit amet"
>>> doc
lorem ipsum
dolor sit amet

line behaves like space if the line break is undone by group:

>>> group doc
lorem ipsum dolor sit amet

line' :: Doc ann

line' is like line, but behaves like mempty if the line break is undone by group (instead of space).

>>> let doc = "lorem ipsum" <> line' <> "dolor sit amet"
>>> doc
lorem ipsum
dolor sit amet
>>> group doc
lorem ipsumdolor sit amet

softline :: Doc ann

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

Here, we have enough space to put everything in one line:

>>> let doc = "lorem ipsum" <> softline <> "dolor sit amet"
>>> putDocW 80 doc
lorem ipsum dolor sit amet

If we narrow the page to width 10, the layouter produces a line break:

>>> putDocW 10 doc
lorem ipsum
dolor sit amet

softline = group line

softline' :: Doc ann

softline' is like softline, but behaves like mempty if the resulting output does not fit on the page (instead of space). In other words, line is to line' how softline is to softline'.

With enough space, we get direct concatenation:

>>> let doc = "ThisWord" <> softline' <> "IsWayTooLong"
>>> putDocW 80 doc
ThisWordIsWayTooLong

If we narrow the page to width 10, the layouter produces a line break:

>>> putDocW 10 doc
ThisWord
IsWayTooLong

softline' = group line'

hardline :: Doc ann

A hardline is always laid out as a line break, even when grouped or when there is plenty of space. Note that it might still be simply discarded if it is part of a flatAlt inside a group.

>>> let doc = "lorem ipsum" <> hardline <> "dolor sit amet"
>>> putDocW 1000 doc
lorem ipsum
dolor sit amet

>>> group doc
lorem ipsum
dolor sit amet

Primitives for alternative layouts

group :: Doc ann -> Doc ann

(group x) tries laying out x into a single line by removing the contained line breaks; if this does not fit the page, or when a hardline within x prevents it from being flattened, x is laid out without any changes.

The group function is key to layouts that adapt to available space nicely.

See vcat, line, or flatAlt for examples that are related, or make good use of it.

flatAlt

Arguments

:: Doc ann

Default

-> Doc ann

Preferred when grouped

-> Doc ann

By default, (flatAlt x y) renders as x. However when grouped, y will be preferred, with x as the fallback for the case when y doesn't fit.

>>> let doc = flatAlt "a" "b"
>>> putDoc doc
a
>>> putDoc (group doc)
b
>>> putDocW 0 (group doc)
a

flatAlt is particularly useful for defining conditional separators such as

softline = group (flatAlt hardline " ")

>>> let hello = "Hello" <> softline <> "world!"
>>> putDocW 12 hello
Hello world!
>>> putDocW 11 hello
Hello
world!

Example: Haskell's do-notation

We can use this to render Haskell's do-notation nicely:

>>> let open        = flatAlt "" "{ "
>>> let close       = flatAlt "" " }"
>>> let separator   = flatAlt "" "; "
>>> let prettyDo xs = group ("do" <+> align (encloseSep open close separator xs))
>>> let statements  = ["name:_ <- getArgs", "let greet = \"Hello, \" <> name", "putStrLn greet"]

This is put into a single line with {;} style if it fits,

>>> putDocW 80 (prettyDo statements)
do { name:_ <- getArgs; let greet = "Hello, " <> name; putStrLn greet }

When there is not enough space the statements are broken up into lines nicely,

>>> putDocW 10 (prettyDo statements)
do name:_ <- getArgs
   let greet = "Hello, " <> name
   putStrLn greet

Notes

Users should be careful to choose x to be less wide than y. Otherwise, if y turns out not to fit the page, we fall back on an even wider layout:

>>> let ugly = group (flatAlt "even wider" "too wide")
>>> putDocW 7 ugly
even wider

Also note that group will flatten y:

>>> putDoc (group (flatAlt "x" ("y" <> line <> "y")))
y y

This also means that an "unflattenable" y which contains a hard linebreak will never be rendered:

>>> putDoc (group (flatAlt "x" ("y" <> hardline <> "y")))
x

Alignment functions

The functions in this section cannot be described by Wadler's original functions. 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 functions from being 'optimal'. In practice however they prove to be very useful. The functions in this section should be used with care, since they are more expensive than the other functions. 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 :: Doc ann -> Doc ann

(align x) lays out the 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. Without alignment, the second line is put simply below everything we've had so far,

>>> "lorem" <+> vsep ["ipsum", "dolor"]
lorem ipsum
dolor

If we add an align to the mix, the vsep's contents all start in the same column,

>>> "lorem" <+> align (vsep ["ipsum", "dolor"])
lorem ipsum
      dolor

hang

Arguments

:: Int

Change of nesting level, relative to the start of the first line

-> Doc ann

-> Doc ann

(hang i x) lays out the document x with a nesting level set to the current column plus i. Negative values are allowed, and decrease the nesting level accordingly.

>>> let doc = reflow "Indenting these words with hang"
>>> putDocW 24 ("prefix" <+> hang 4 doc)
prefix Indenting these
           words with
           hang

This differs from nest, which is based on the current nesting level plus i. When you're not sure, try the more efficient nest first. In our example, this would yield

>>> let doc = reflow "Indenting these words with nest"
>>> putDocW 24 ("prefix" <+> nest 4 doc)
prefix Indenting these
    words with nest

hang i doc = align (nest i doc)

indent

Arguments

:: Int

Number of spaces to increase indentation by

-> Doc ann

-> Doc ann

(indent i x) indents document x by i columns, starting from the current cursor position.

>>> let doc = reflow "The indent function indents these words!"
>>> putDocW 24 ("prefix" <> indent 4 doc)
prefix    The indent
          function
          indents these
          words!

indent i d = hang i ({i spaces} <> d)

encloseSep

Arguments

:: Doc ann

left delimiter

-> Doc ann

right delimiter

-> Doc ann

separator

-> [Doc ann]

input documents

-> Doc ann

(encloseSep l r sep xs) concatenates the documents xs separated by sep, and encloses the resulting document by l and r.

The documents are laid out horizontally if that fits the page,

>>> let doc = "list" <+> align (encloseSep lbracket rbracket comma (map pretty [1,20,300,4000]))
>>> putDocW 80 doc
list [1,20,300,4000]

If there is not enough space, then the input is split into lines entry-wise therwise they are laid out vertically, with separators put in the front:

>>> putDocW 10 doc
list [1
     ,20
     ,300
     ,4000]

Note that doc contains an explicit call to align so that the list items are aligned vertically.

For putting separators at the end of entries instead, have a look at punctuate.

list :: [Doc ann] -> Doc ann

Haskell-inspired variant of encloseSep with braces and comma as separator.

>>> let doc = list (map pretty [1,20,300,4000])

>>> putDocW 80 doc
[1, 20, 300, 4000]

>>> putDocW 10 doc
[ 1
, 20
, 300
, 4000 ]

tupled :: [Doc ann] -> Doc ann

Haskell-inspired variant of encloseSep with parentheses and comma as separator.

>>> let doc = tupled (map pretty [1,20,300,4000])

>>> putDocW 80 doc
(1, 20, 300, 4000)

>>> putDocW 10 doc
( 1
, 20
, 300
, 4000 )

Binary functions

(<>) :: Semigroup a => a -> a -> a infixr 6

An associative operation.

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

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

>>> "hello" <+> "world"
hello world

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

List functions

The sep and cat functions differ in one detail: when grouped, the seps replace newlines wich spaces, while the cats simply remove them. If you're not sure what you want, start with the seps.

concatWith :: Foldable t => (Doc ann -> Doc ann -> Doc ann) -> t (Doc ann) -> Doc ann

Concatenate all documents element-wise with a binary function.

concatWith _ [] = mempty
concatWith (**) [x,y,z] = x ** y ** z

Multiple convenience definitions based on concatWith are alredy predefined, for example

hsep    = concatWith (<+>)
fillSep = concatWith (\x y -> x <> softline <> y)

This is also useful to define customized joiners,

>>> concatWith (surround dot) ["Prettyprinter", "Render", "Text"]
Prettyprinter.Render.Text

sep family

When grouped, these will replace newlines with spaces.

hsep :: [Doc ann] -> Doc ann

(hsep xs) concatenates all documents xs horizontally with <+>, i.e. it puts a space between all entries.

>>> let docs = Util.words "lorem ipsum dolor sit amet"

>>> hsep docs
lorem ipsum dolor sit amet

hsep does not introduce line breaks on its own, even when the page is too narrow:

>>> putDocW 5 (hsep docs)
lorem ipsum dolor sit amet

For automatic line breaks, consider using fillSep instead.

vsep :: [Doc ann] -> Doc ann

(vsep xs) concatenates all documents xs above each other. If a group undoes the line breaks inserted by vsep, the documents are separated with a space instead.

Using vsep alone yields

>>> "prefix" <+> vsep ["text", "to", "lay", "out"]
prefix text
to
lay
out

grouping a vsep separates the documents with a space if it fits the page (and does nothing otherwise). See the sep convenience function for this use case.

The align function can be used to align the documents under their first element:

>>> "prefix" <+> align (vsep ["text", "to", "lay", "out"])
prefix text
       to
       lay
       out

Since grouping a vsep is rather common, sep is a built-in for doing that.

fillSep :: [Doc ann] -> Doc ann

(fillSep xs) concatenates the documents xs horizontally with <+> as long as it fits the page, then inserts a line and continues doing that for all documents in xs. (line means that if grouped, the documents are separated with a space instead of newlines. Use fillCat if you do not want a space.)

Let's print some words to fill the line:

>>> let docs = take 20 (cycle ["lorem", "ipsum", "dolor", "sit", "amet"])
>>> putDocW 80 ("Docs:" <+> fillSep docs)
Docs: lorem ipsum dolor sit amet lorem ipsum dolor sit amet lorem ipsum dolor
sit amet lorem ipsum dolor sit amet

The same document, printed at a width of only 40, yields

>>> putDocW 40 ("Docs:" <+> fillSep docs)
Docs: lorem ipsum dolor sit amet lorem
ipsum dolor sit amet lorem ipsum dolor
sit amet lorem ipsum dolor sit amet

sep :: [Doc ann] -> Doc ann

(sep xs) tries laying out the documents xs separated with spaces, and if this does not fit the page, separates them with newlines. This is what differentiates it from vsep, which always lays out its contents beneath each other.

>>> let doc = "prefix" <+> sep ["text", "to", "lay", "out"]
>>> putDocW 80 doc
prefix text to lay out

With a narrower layout, the entries are separated by newlines:

>>> putDocW 20 doc
prefix text
to
lay
out

sep = group . vsep

cat family

When grouped, these will remove newlines.

hcat :: [Doc ann] -> Doc ann

(hcat xs) concatenates all documents xs horizontally with <> (i.e. without any spacing).

It is provided only for consistency, since it is identical to mconcat.

>>> let docs = Util.words "lorem ipsum dolor"
>>> hcat docs
loremipsumdolor

vcat :: [Doc ann] -> Doc ann

(vcat xs) vertically concatenates the documents xs. If it is grouped, the line breaks are removed.

In other words vcat is like vsep, with newlines removed instead of replaced by spaces.

>>> let docs = Util.words "lorem ipsum dolor"
>>> vcat docs
lorem
ipsum
dolor
>>> group (vcat docs)
loremipsumdolor

Since grouping a vcat is rather common, cat is a built-in shortcut for it.

fillCat :: [Doc ann] -> Doc ann

(fillCat xs) concatenates documents xs horizontally with <> as long as it fits the page, then inserts a line' and continues doing that for all documents in xs. This is similar to how an ordinary word processor lays out the text if you just keep typing after you hit the maximum line length.

(line' means that if grouped, the documents are separated with nothing instead of newlines. See fillSep if you want a space instead.)

Observe the difference between fillSep and fillCat. fillSep concatenates the entries spaced when grouped,

>>> let docs = take 20 (cycle (["lorem", "ipsum", "dolor", "sit", "amet"]))
>>> putDocW 40 ("Grouped:" <+> group (fillSep docs))
Grouped: lorem ipsum dolor sit amet
lorem ipsum dolor sit amet lorem ipsum
dolor sit amet lorem ipsum dolor sit
amet

On the other hand, fillCat concatenates the entries directly when grouped,

>>> putDocW 40 ("Grouped:" <+> group (fillCat docs))
Grouped: loremipsumdolorsitametlorem
ipsumdolorsitametloremipsumdolorsitamet
loremipsumdolorsitamet

cat :: [Doc ann] -> Doc ann

(cat xs) tries laying out the documents xs separated with nothing, and if this does not fit the page, separates them with newlines. This is what differentiates it from vcat, which always lays out its contents beneath each other.

>>> let docs = Util.words "lorem ipsum dolor"
>>> putDocW 80 ("Docs:" <+> cat docs)
Docs: loremipsumdolor

When there is enough space, the documents are put above one another,

>>> putDocW 10 ("Docs:" <+> cat docs)
Docs: lorem
ipsum
dolor

cat = group . vcat

Others

punctuate

Arguments

:: Doc ann

Punctuation, e.g. comma

-> [Doc ann]

-> [Doc ann]

(punctuate p xs) appends p to all but the last document in xs.

>>> let docs = punctuate comma (Util.words "lorem ipsum dolor sit amet")
>>> putDocW 80 (hsep docs)
lorem, ipsum, dolor, sit, amet

The separators are put at the end of the entries, which we can see if we position the result vertically:

>>> putDocW 20 (vsep docs)
lorem,
ipsum,
dolor,
sit,
amet

If you want put the commas in front of their elements instead of at the end, you should use tupled or, in general, encloseSep.

Reactive/conditional layouts

Lay documents out differently based on current position and the page layout.

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

Layout a document depending on which column it starts at. align is implemented in terms of column.

>>> column (\l -> "Columns are" <+> pretty l <> "-based.")
Columns are 0-based.

>>> let doc = "prefix" <+> column (\l -> "| <- column" <+> pretty l)
>>> vsep [indent n doc | n <- [0,4,8]]
prefix | <- column 7
    prefix | <- column 11
        prefix | <- column 15

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

Layout a document depending on the current nesting level. align is implemented in terms of nesting.

>>> let doc = "prefix" <+> nesting (\l -> brackets ("Nested:" <+> pretty l))
>>> vsep [indent n doc | n <- [0,4,8]]
prefix [Nested: 0]
    prefix [Nested: 4]
        prefix [Nested: 8]

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

(width doc f) lays out the document doc, and makes the column width of it available to a function.

>>> let annotate doc = width (brackets doc) (\w -> " <- width:" <+> pretty w)
>>> align (vsep (map annotate ["---", "------", indent 3 "---", vsep ["---", indent 4 "---"]]))
[---] <- width: 5
[------] <- width: 8
[   ---] <- width: 8
[---
    ---] <- width: 8

pageWidth :: (PageWidth -> Doc ann) -> Doc ann

Layout a document depending on the page width, if one has been specified.

>>> let prettyPageWidth (AvailablePerLine l r) = "Width:" <+> pretty l <> ", ribbon fraction:" <+> pretty r
>>> let doc = "prefix" <+> pageWidth (brackets . prettyPageWidth)
>>> putDocW 32 (vsep [indent n doc | n <- [0,4,8]])
prefix [Width: 32, ribbon fraction: 1.0]
    prefix [Width: 32, ribbon fraction: 1.0]
        prefix [Width: 32, ribbon fraction: 1.0]

Filler functions

Fill up available space

fill

Arguments

:: Int

Append spaces until the document is at least this wide

-> Doc ann

-> Doc ann

(fill i x) lays out the 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 function is quite useful in practice to output a list of bindings:

>>> let types = [("empty","Doc"), ("nest","Int -> Doc -> Doc"), ("fillSep","[Doc] -> Doc")]
>>> let ptype (name, tp) = fill 5 (pretty name) <+> "::" <+> pretty tp
>>> "let" <+> align (vcat (map ptype types))
let empty :: Doc
    nest  :: Int -> Doc -> Doc
    fillSep :: [Doc] -> Doc

fillBreak

Arguments

:: Int

Append spaces until the document is at least this wide

-> Doc ann

-> Doc ann

(fillBreak i x) first lays out the 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 example given in fill to use fillBreak, we get a useful variation of the output:

>>> let types = [("empty","Doc"), ("nest","Int -> Doc -> Doc"), ("fillSep","[Doc] -> Doc")]
>>> let ptype (name, tp) = fillBreak 5 (pretty name) <+> "::" <+> pretty tp
>>> "let" <+> align (vcat (map ptype types))
let empty :: Doc
    nest  :: Int -> Doc -> Doc
    fillSep
          :: [Doc] -> Doc

General convenience

Useful helper functions.

plural

Arguments

:: (Num amount, Eq amount)

=> doc

1 case

-> doc

other cases

-> amount

-> doc

(plural n one many) is one if n is 1, and many otherwise. A typical use case is adding a plural "s".

>>> let things = [True]
>>> let amount = length things
>>> pretty things <+> "has" <+> pretty amount <+> plural "entry" "entries" amount
[True] has 1 entry

enclose

Arguments

:: Doc ann

L

-> Doc ann

R

-> Doc ann

x

-> Doc ann

LxR

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

>>> enclose "A" "Z" "·"
A·Z

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

surround :: Doc ann -> Doc ann -> Doc ann -> Doc ann

(surround x l r) surrounds document x with l and r.

>>> surround "·" "A" "Z"
A·Z

This is merely an argument reordering of enclose, but allows for definitions like

>>> concatWith (surround dot) ["Prettyprinter", "Render", "Text"]
Prettyprinter.Render.Text

Bracketing functions

Enclose documents in common ways.

squotes :: Doc ann -> Doc ann

>>> squotes "·"
'·'

dquotes :: Doc ann -> Doc ann

>>> dquotes "·"
"·"

parens :: Doc ann -> Doc ann

>>> parens "·"
(·)

angles :: Doc ann -> Doc ann

>>> angles "·"
<·>

brackets :: Doc ann -> Doc ann

>>> brackets "·"
[·]

braces :: Doc ann -> Doc ann

>>> braces "·"
{·}

Named characters

Convenience definitions for common characters

lparen :: Doc ann

>>> lparen
(

rparen :: Doc ann

>>> rparen
)

langle :: Doc ann

>>> langle
<

rangle :: Doc ann

>>> rangle
>

lbrace :: Doc ann

>>> lbrace
{

rbrace :: Doc ann

>>> rbrace
}

lbracket :: Doc ann

>>> lbracket
[

rbracket :: Doc ann

>>> rbracket
]

squote :: Doc ann

>>> squote
'

dquote :: Doc ann

>>> dquote
"

semi :: Doc ann

>>> semi
;

colon :: Doc ann

>>> colon
:

comma :: Doc ann

>>> comma
,

space :: Doc ann

>>> "a" <> space <> "b"
a b

This is mostly used via <+>,

>>> "a" <+> "b"
a b

dot :: Doc ann

>>> dot
.

slash :: Doc ann

>>> slash
/

backslash :: Doc ann

>>> backslash
\

equals :: Doc ann

>>> equals
=

pipe :: Doc ann

>>> pipe
|

Annotations

annotate :: ann -> Doc ann -> Doc ann

Add an annotation to a Doc. This annotation can then be used by the renderer to e.g. add color to certain parts of the output. For a full tutorial example on how to use it, see the Prettyprinter.Render.Tutorials.StackMachineTutorial or Prettyprinter.Render.Tutorials.TreeRenderingTutorial modules.

This function is only relevant for custom formats with their own annotations, and not relevant for basic prettyprinting. The predefined renderers, e.g. Prettyprinter.Render.Text, should be enough for the most common needs.

unAnnotate :: Doc ann -> Doc xxx

Remove all annotations.

Although unAnnotate is idempotent with respect to rendering,

unAnnotate . unAnnotate = unAnnotate

it should not be used without caution, for each invocation traverses the entire contained document. If possible, it is preferrable to unannotate after producing the layout by using unAnnotateS.

reAnnotate :: (ann -> ann') -> Doc ann -> Doc ann'

Change the annotation of a Document.

Useful in particular to embed documents with one form of annotation in a more generlly annotated document.

Since this traverses the entire Doc tree, including parts that are not rendered due to other layouts fitting better, it is preferrable to reannotate after producing the layout by using reAnnotateS.

Since reAnnotate has the right type and satisfies 'reAnnotate id = id', it is used to define the Functor instance of Doc.

alterAnnotations :: (ann -> [ann']) -> Doc ann -> Doc ann'

Change the annotations of a Document. Individual annotations can be removed, changed, or replaced by multiple ones.

This is a general function that combines unAnnotate and reAnnotate, and it is useful for mapping semantic annotations (such as »this is a keyword«) to display annotations (such as »this is red and underlined«), because some backends may not care about certain annotations, while others may.

Annotations earlier in the new list will be applied earlier, i.e. returning [Bold, Green] will result in a bold document that contains green text, and not vice-versa.

Since this traverses the entire Doc tree, including parts that are not rendered due to other layouts fitting better, it is preferrable to reannotate after producing the layout by using alterAnnotationsS.

unAnnotateS :: SimpleDocStream ann -> SimpleDocStream xxx

Remove all annotations. unAnnotate for SimpleDocStream.

reAnnotateS :: (ann -> ann') -> SimpleDocStream ann -> SimpleDocStream ann'

Change the annotation of a document. reAnnotate for SimpleDocStream.

alterAnnotationsS :: (ann -> Maybe ann') -> SimpleDocStream ann -> SimpleDocStream ann'

Change the annotation of a document to a different annotation, or none at all. alterAnnotations for SimpleDocStream.

Note that the Doc version is more flexible, since it allows changing a single annotation to multiple ones. (SimpleDocTree restores this flexibility again.)

Optimization

fuse :: FusionDepth -> Doc ann -> Doc ann

(fuse depth doc) combines text nodes so they can be rendered more efficiently. A fused document is always laid out identical to its unfused version.

When laying a Document out to a SimpleDocStream, every component of the input is translated directly to the simpler output format. This sometimes yields undesirable chunking when many pieces have been concatenated together.

For example

>>> "a" <> "b" <> pretty 'c' <> "d"
abcd

results in a chain of four entries in a SimpleDocStream, although this is fully equivalent to the tightly packed

>>> "abcd" :: Doc ann
abcd

which is only a single SimpleDocStream entry, and can be processed faster.

It is therefore a good idea to run fuse on concatenations of lots of small strings that are used many times,

>>> let oftenUsed = fuse Shallow ("a" <> "b" <> pretty 'c' <> "d")
>>> hsep (replicate 5 oftenUsed)
abcd abcd abcd abcd abcd

data FusionDepth

Fusion depth parameter, used by fuse.

Constructors

Shallow

Do not dive deep into nested documents, fusing mostly concatenations of text nodes together.

Deep

Recurse into all parts of the Doc, including different layout alternatives, and location-sensitive values such as created by nesting which cannot be fused before, but only during, the layout process. As a result, the performance cost of using deep fusion is often hard to predict, and depends on the interplay between page layout and document to prettyprint.

This value should only be used if profiling shows it is significantly faster than using Shallow.

Instances

Eq FusionDepth

Defined in Prettyprinter.Internal

Methods

(==) :: FusionDepth -> FusionDepth -> Bool

(/=) :: FusionDepth -> FusionDepth -> Bool

Ord FusionDepth

Defined in Prettyprinter.Internal

Methods

compare :: FusionDepth -> FusionDepth -> Ordering

(<) :: FusionDepth -> FusionDepth -> Bool

(<=) :: FusionDepth -> FusionDepth -> Bool

(>) :: FusionDepth -> FusionDepth -> Bool

(>=) :: FusionDepth -> FusionDepth -> Bool

max :: FusionDepth -> FusionDepth -> FusionDepth

min :: FusionDepth -> FusionDepth -> FusionDepth

Show FusionDepth

Defined in Prettyprinter.Internal

Methods

showsPrec :: Int -> FusionDepth -> ShowS

show :: FusionDepth -> String

showList :: [FusionDepth] -> ShowS

Layout

Laying a Document out produces a straightforward SimpleDocStream based on parameters such as page width and ribbon size, by evaluating how a Doc fits these constraints the best. There are various ways to render a SimpleDocStream. For the common case of rendering a SimpleDocStream as plain Text take a look at Prettyprinter.Render.Text.

data SimpleDocStream ann

The data type SimpleDocStream represents laid out documents and is used by the display functions.

A simplified view is that Doc = [SimpleDocStream], and the layout functions pick one of the SimpleDocStreams based on which one fits the layout constraints best. This means that SimpleDocStream has all complexity contained in Doc resolved, making it very easy to convert it to other formats, such as plain text or terminal output.

To write your own Doc to X converter, it is therefore sufficient to convert from SimpleDocStream. The »Render« submodules provide some built-in converters to do so, and helpers to create own ones.

Constructors

SFail

SEmpty

SChar !Char (SimpleDocStream ann)

SText !Int !Text (SimpleDocStream ann)

length is O(n), so we cache it in the Int field.

SLine !Int (SimpleDocStream ann)

Int = indentation level for the (next) line

SAnnPush ann (SimpleDocStream ann)

Add an annotation to the remaining document.

SAnnPop (SimpleDocStream ann)

Remove a previously pushed annotation.

Instances

Functor SimpleDocStream

Alter the document’s annotations.

This instance makes SimpleDocStream more flexible (because it can be used in Functor-polymorphic values), but fmap is much less readable compared to using reAnnotateST in code that only works for SimpleDocStream anyway. Consider using the latter when the type does not matter.

Defined in Prettyprinter.Internal

Methods

fmap :: (a -> b) -> SimpleDocStream a -> SimpleDocStream b

(<$) :: a -> SimpleDocStream b -> SimpleDocStream a

Foldable SimpleDocStream

Collect all annotations from a document.

Defined in Prettyprinter.Internal

Methods

fold :: Monoid m => SimpleDocStream m -> m

foldMap :: Monoid m => (a -> m) -> SimpleDocStream a -> m

foldr :: (a -> b -> b) -> b -> SimpleDocStream a -> b

foldr' :: (a -> b -> b) -> b -> SimpleDocStream a -> b

foldl :: (b -> a -> b) -> b -> SimpleDocStream a -> b

foldl' :: (b -> a -> b) -> b -> SimpleDocStream a -> b

foldr1 :: (a -> a -> a) -> SimpleDocStream a -> a

foldl1 :: (a -> a -> a) -> SimpleDocStream a -> a

toList :: SimpleDocStream a -> [a]

null :: SimpleDocStream a -> Bool

length :: SimpleDocStream a -> Int

elem :: Eq a => a -> SimpleDocStream a -> Bool

maximum :: Ord a => SimpleDocStream a -> a

minimum :: Ord a => SimpleDocStream a -> a

sum :: Num a => SimpleDocStream a -> a

product :: Num a => SimpleDocStream a -> a

Traversable SimpleDocStream

Transform a document based on its annotations, possibly leveraging Applicative effects.

Defined in Prettyprinter.Internal

Methods

traverse :: Applicative f => (a -> f b) -> SimpleDocStream a -> f (SimpleDocStream b)

sequenceA :: Applicative f => SimpleDocStream (f a) -> f (SimpleDocStream a)

mapM :: Monad m => (a -> m b) -> SimpleDocStream a -> m (SimpleDocStream b)

sequence :: Monad m => SimpleDocStream (m a) -> m (SimpleDocStream a)

Eq ann => Eq (SimpleDocStream ann)

Defined in Prettyprinter.Internal

Methods

(==) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

(/=) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

Ord ann => Ord (SimpleDocStream ann)

Defined in Prettyprinter.Internal

Methods

compare :: SimpleDocStream ann -> SimpleDocStream ann -> Ordering

(<) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

(<=) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

(>) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

(>=) :: SimpleDocStream ann -> SimpleDocStream ann -> Bool

max :: SimpleDocStream ann -> SimpleDocStream ann -> SimpleDocStream ann

min :: SimpleDocStream ann -> SimpleDocStream ann -> SimpleDocStream ann

Show ann => Show (SimpleDocStream ann)

Defined in Prettyprinter.Internal

Methods

showsPrec :: Int -> SimpleDocStream ann -> ShowS

show :: SimpleDocStream ann -> String

showList :: [SimpleDocStream ann] -> ShowS

Generic (SimpleDocStream ann)

Defined in Prettyprinter.Internal

Associated Types

type Rep (SimpleDocStream ann) :: Type -> Type

Methods

from :: SimpleDocStream ann -> Rep (SimpleDocStream ann) x

to :: Rep (SimpleDocStream ann) x -> SimpleDocStream ann

type Rep (SimpleDocStream ann)

Defined in Prettyprinter.Internal

type Rep (SimpleDocStream ann) = D1 (MetaData "SimpleDocStream" "Prettyprinter.Internal" "prettyprinter-1.7.0-3a58dVee6cSUUePu4NnX6" False) ((C1 (MetaCons "SFail" PrefixI False) (U1 :: Type -> Type) :+: (C1 (MetaCons "SEmpty" PrefixI False) (U1 :: Type -> Type) :+: C1 (MetaCons "SChar" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Char) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (SimpleDocStream ann))))) :+: ((C1 (MetaCons "SText" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Int) :*: (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Text) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (SimpleDocStream ann)))) :+: C1 (MetaCons "SLine" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Int) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (SimpleDocStream ann)))) :+: (C1 (MetaCons "SAnnPush" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 ann) :*: S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (SimpleDocStream ann))) :+: C1 (MetaCons "SAnnPop" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (SimpleDocStream ann))))))

data PageWidth

Maximum number of characters that fit in one line. The layout algorithms will try not to exceed the set limit by inserting line breaks when applicable (e.g. via softline').

Constructors

AvailablePerLine !Int !Double

Layouters should not exceed the specified space per line.

• The Int is the number of characters, including whitespace, that fit in a line. A typical value is 80.
• The Double is the ribbon with, i.e. the fraction of the total page width that can be printed on. This allows limiting the length of printable text per line. Values must be between 0 and 1, and 0.4 to 1 is typical.

Unbounded

Layouters should not introduce line breaks on their own.

Instances

Eq PageWidth

Defined in Prettyprinter.Internal

Methods

(==) :: PageWidth -> PageWidth -> Bool

(/=) :: PageWidth -> PageWidth -> Bool

Ord PageWidth

Defined in Prettyprinter.Internal

Methods

compare :: PageWidth -> PageWidth -> Ordering

(<) :: PageWidth -> PageWidth -> Bool

(<=) :: PageWidth -> PageWidth -> Bool

(>) :: PageWidth -> PageWidth -> Bool

(>=) :: PageWidth -> PageWidth -> Bool

max :: PageWidth -> PageWidth -> PageWidth

min :: PageWidth -> PageWidth -> PageWidth

Show PageWidth

Defined in Prettyprinter.Internal

Methods

showsPrec :: Int -> PageWidth -> ShowS

show :: PageWidth -> String

showList :: [PageWidth] -> ShowS

newtype LayoutOptions

Options to influence the layout algorithms.

Constructors

LayoutOptions

Fields

• layoutPageWidth :: PageWidth

Instances

Eq LayoutOptions

Defined in Prettyprinter.Internal

Methods

(==) :: LayoutOptions -> LayoutOptions -> Bool

(/=) :: LayoutOptions -> LayoutOptions -> Bool

Ord LayoutOptions

Defined in Prettyprinter.Internal

Methods

compare :: LayoutOptions -> LayoutOptions -> Ordering

(<) :: LayoutOptions -> LayoutOptions -> Bool

(<=) :: LayoutOptions -> LayoutOptions -> Bool

(>) :: LayoutOptions -> LayoutOptions -> Bool

(>=) :: LayoutOptions -> LayoutOptions -> Bool

max :: LayoutOptions -> LayoutOptions -> LayoutOptions

min :: LayoutOptions -> LayoutOptions -> LayoutOptions

Show LayoutOptions

Defined in Prettyprinter.Internal

Methods

showsPrec :: Int -> LayoutOptions -> ShowS

show :: LayoutOptions -> String

showList :: [LayoutOptions] -> ShowS

defaultLayoutOptions :: LayoutOptions

The default layout options, suitable when you just want some output, and don’t particularly care about the details. Used by the Show instance, for example.

>>> defaultLayoutOptions
LayoutOptions {layoutPageWidth = AvailablePerLine 80 1.0}

layoutPretty :: LayoutOptions -> Doc ann -> SimpleDocStream ann

This is the default layout algorithm, and it is used by show, putDoc and hPutDoc.

layoutPretty commits to rendering something in a certain way if the next element fits the layout constraints; in other words, it has one SimpleDocStream element lookahead when rendering. Consider using the smarter, but a bit less performant, layoutSmart algorithm if the results seem to run off to the right before having lots of line breaks.

layoutCompact :: Doc ann1 -> SimpleDocStream ann2

(layoutCompact x) lays out the document x without adding any indentation and without preserving annotations. Since no 'pretty' printing is involved, this layouter is very fast. The resulting output contains fewer characters than a prettyprinted version and can be used for output that is read by other programs.

>>> let doc = hang 4 (vsep ["lorem", "ipsum", hang 4 (vsep ["dolor", "sit"])])
>>> doc
lorem
    ipsum
    dolor
        sit

>>> let putDocCompact = renderIO System.IO.stdout . layoutCompact
>>> putDocCompact doc
lorem
ipsum
dolor
sit

layoutSmart :: LayoutOptions -> Doc ann -> SimpleDocStream ann

A layout algorithm with more lookahead than layoutPretty, that introduces line breaks earlier if the content does not (or will not, rather) fit into one line.

Consider the following python-ish document,

>>> let fun x = hang 2 ("fun(" <> softline' <> x) <> ")"
>>> let doc = (fun . fun . fun . fun . fun) (align (list ["abcdef", "ghijklm"]))

which we’ll be rendering using the following pipeline (where the layout algorithm has been left open),

>>> import Data.Text.IO as T
>>> import Prettyprinter.Render.Text
>>> let hr = pipe <> pretty (replicate (26-2) '-') <> pipe
>>> let go layouter x = (T.putStrLn . renderStrict . layouter (LayoutOptions (AvailablePerLine 26 1))) (vsep [hr, x, hr])

If we render this using layoutPretty with a page width of 26 characters per line, all the fun calls fit into the first line so they will be put there,

>>> go layoutPretty doc
|------------------------|
fun(fun(fun(fun(fun(
                  [ abcdef
                  , ghijklm ])))))
|------------------------|

Note that this exceeds the desired 26 character page width. The same document, rendered with layoutSmart, fits the layout contstraints:

>>> go layoutSmart doc
|------------------------|
fun(
  fun(
    fun(
      fun(
        fun(
          [ abcdef
          , ghijklm ])))))
|------------------------|

The key difference between layoutPretty and layoutSmart is that the latter will check the potential document until it encounters a line with the same indentation or less than the start of the document. Any line encountered earlier is assumed to belong to the same syntactic structure. layoutPretty checks only the first line.

Consider for example the question of whether the As fit into the document below:

1 A
2   A
3  A
4 B
5   B

layoutPretty will check only line 1, ignoring whether e.g. line 2 might already be too wide. By contrast, layoutSmart stops only once it reaches line 4, where the B has the same indentation as the first A.

removeTrailingWhitespace :: SimpleDocStream ann -> SimpleDocStream ann

Remove all trailing space characters.

This has some performance impact, because it does an entire additional pass over the SimpleDocStream.

No trimming will be done inside annotations, which are considered to contain no (trimmable) whitespace, since the annotation might actually be about the whitespace, for example a renderer that colors the background of trailing whitespace, as e.g. git diff can be configured to do.

Historical note: Since v1.7.0, layoutPretty and layoutSmart avoid producing the trailing whitespace that was the original motivation for creating removeTrailingWhitespace. See https://github.com/quchen/prettyprinter/pull/139 for some background info.

Migration guide

There are 3 main ways to migrate:

1. Direct: just replace the previous package and fix the errors
2. Using a drop-in replacement mimicing the API of the former module, see the prettyprinter-compat-package packages
3. Using a converter from the old Doc type to the new one, see the prettyprinter-convert-package packages

If you're already familiar with (ansi-)wl-pprint, you'll recognize many functions in this module, and they work just the same way. However, a couple of definitions are missing:

• char, string, double, … – these are all special cases of the overloaded pretty function.
• <$>, <$$>, </>, <//> are special cases of vsep, vcat, fillSep, fillCat with only two documents.
• If you need String output, use the backends in the Prettyprinter.Render.String module.
• The display functions are moved to the rendering submodules, for example conversion to plain Text is in the Prettyprinter.Render.Text module.
• The render functions are called layout functions.
• SimpleDoc was renamed to SimpleDocStream, in order to make it clearer in the presence of SimpleDocTree.
• Instead of providing an own colorization function for each color/intensity/layer combination, they have been combined in color, colorDull, bgColor, and bgColorDull functions, which can be found in the ANSI terminal specific prettyprinter-ansi-terminal package.