Options.Applicative.Help.Pretty

Overloaded conversion to Doc.

Laws:

1. output should be pretty. :-)

(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.

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.

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 doca>>> 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 helloHello world!>>> putDocW 11 helloHelloworld!

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 uglyeven 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

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

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

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

>>> group doclorem ipsum dolor sit amet

An associative operation.

Examples

>>> [1,2,3] <> [4,5,6][1,2,3,4,5,6]

>>> Just [1, 2, 3] <> Just [4, 5, 6]Just [1,2,3,4,5,6]

>>> putStr "Hello, " <> putStrLn "World!"Hello, World!

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 doclorem ipsum dolor sit amet

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

>>> putDocW 10 doclorem ipsumdolor sit amet

softline = group line

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]

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

(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    dolorsitamet

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).

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

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

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

(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 ipsumdolor

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

(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)

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.

Options to influence the layout algorithms.

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').

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 ]

Fusion depth parameter, used by fuse.

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.

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.)

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.

(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: loremipsumdolor

cat = group . vcat

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 already 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

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.

>>> defaultLayoutOptionsLayoutOptions {layoutPageWidth = AvailablePerLine 80 1.0}

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.

(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

(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 doclist [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 doclist [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.

(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 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

(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 ametlorem ipsum dolor sit amet lorem ipsumdolor sit amet lorem ipsum dolor sitamet

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

>>> putDocW 40 ("Grouped:" <+> group (fillCat docs))Grouped: loremipsumdolorsitametloremipsumdolorsitametloremipsumdolorsitametloremipsumdolorsitamet

(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 dolorsit 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 loremipsum dolor sit amet lorem ipsum dolorsit amet lorem ipsum dolor sit amet

(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 annabcd

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

(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)

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 doclorem ipsumdolor sit amet

>>> group doclorem ipsumdolor sit amet

(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 docsloremipsumdolor

(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 docslorem 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.

(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"])])>>> doclorem    ipsum    dolor        sit

>>> let putDocCompact = renderIO System.IO.stdout . layoutCompact>>> putDocCompact docloremipsumdolorsit

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.

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">>> doclorem ipsumdolor sit amet>>> group doclorem ipsumdolor sit amet

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]

(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

(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.

Change the annotation of a Document.

Useful in particular to embed documents with one form of annotation in a more generally 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.

Change the annotation of a document. reAnnotate for SimpleDocStream.

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.

(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 docprefix text to lay out

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

>>> putDocW 20 docprefix texttolayout

sep = group . vsep

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 docThisWordIsWayTooLong

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

>>> putDocW 10 docThisWordIsWayTooLong

softline' = group line'

(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

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 )

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.

Remove all annotations. unAnnotate for SimpleDocStream.

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

(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 docsloremipsumdolor>>> group (vcat docs)loremipsumdolor

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

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

(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 texttolayout

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.

(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

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

This is mostly used via <+>,

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

Render the annotated document in a certain style. Styles not set in the annotation will use the style of the surrounding document, or the terminal’s default if none has been set yet.

style = color Green <> bold
styledDoc = annotate style "hello world"

The 8 ANSI terminal colors.

Dull or vivid coloring, as supported by ANSI terminals.

Style the background with a vivid color.

Style the background with a dull color.

Render in bold.

Style the foreground with a vivid color.

Style the foreground with a dull color.

Like putDoc, but instead of using stdout, print to a user-provided handle, e.g. a file or a socket using defaultLayoutOptions.

main = withFile "someFile.txt" (\h -> hPutDoc h (vcat ["vertical", "text"]))

hPutDoc h doc = renderIO h (layoutPretty defaultLayoutOptions doc)

Render in italics.

(putDoc doc) prettyprints document doc to standard output using defaultLayoutOptions.

>>> putDoc ("hello" <+> "world")hello world

putDoc = hPutDoc stdout

(renderIO h sdoc) writes sdoc to the handle h.

>>> let render = renderIO System.IO.stdout . layoutPretty defaultLayoutOptions>>> let doc = annotate (color Red) ("red" <+> align (vsep [annotate (color Blue <> underlined) ("blue+u" <+> annotate bold "bold" <+> "blue+u"), "red"]))

We render the unAnnotated version here, since the ANSI codes don’t display well in Haddock,

>>> render (unAnnotate doc)red blue+u bold blue+u    red

This function behaves just like

renderIO h sdoc = TL.hPutStr h (renderLazy sdoc)

but will not generate any intermediate text, rendering directly to the handle.

(renderLazy doc) takes the output doc from a rendering function and transforms it to lazy text, including ANSI styling directives for things like colorization.

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.

With a bit of trickery to make the ANSI codes printable, here is an example that would render colored in an ANSI terminal:

>>> let render = TL.putStrLn . TL.replace "\ESC" "\\e" . renderLazy . layoutPretty defaultLayoutOptions>>> let doc = annotate (color Red) ("red" <+> align (vsep [annotate (color Blue <> underlined) ("blue+u" <+> annotate bold "bold" <+> "blue+u"), "red"]))>>> render (unAnnotate doc)red blue+u bold blue+u    red>>> render doc\e[0;91mred \e[0;94;4mblue+u \e[0;94;1;4mbold\e[0;94;4m blue+u\e[0;91m    red\e[0m

Run the above via echo -e ... in your terminal to see the coloring.

(renderStrict sdoc) takes the output sdoc from a rendering and transforms it to strict text.

Render underlined.

Render flattened text on this line, or start a new line before rendering any text.

This will also nest subsequent lines in the group.

Separate items in an alternative with a pipe.

If the first document and the pipe don't fit on the line, then mandatorily flow the next entry onto the following line.

The (//) softbreak ensures that if the document does fit on the line, there is at least a space, but it's possible for y to still appear on the next line.

Printer hacks to get nice indentation for long commands and subcommands.

If we're starting this section over the desired width   (usually 1/3 of the ribbon), then we will make a line break, indent all of the usage, and go.

The ifAtRoot is an interesting clause. If this whole operation is put under a group then the linebreak will disappear; then item d will therefore not be at the starting column, and it won't be indented more.