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≡ ■ Prettier Printer · GitHub stars npm

A pretty printing library for text documents that can be rendered to a desired maximum width. Basic features:

As an example, the evaluation output in this live CodeSandbox example is formatted using this library.

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≡ ■ Contents

≡ ■ Tutorial

To be done.

In the meanwhile, read Philip Wadler's paper A prettier printer.

≡ ■ Reference

Typically one imports the library as:

import * as PP from 'prettier-printer'

The examples also utilize Ramda, bound as R.

≡ ■ Rendering documents

≡ ■ PP.render(maxCols, doc) ~> string v1.0.0

PP.render renders the document to a string trying to keep the width of the document within the specified maximum. A width of 0 means that there is no maximum. See also PP.renderWith.

For example:

PP.render(
  10,
  PP.indent('-- ', PP.group(PP.intersperse(PP.line, ['Hello,', 'world!'])))
)

≡ ■ PP.renderWith({text: (state, string) => state, line: state => state}, state, maxCols, doc) ~> state v1.0.0

PP.renderWith renders the document with the given actions text and line. You can use this function to output the document without creating an intermediate string of the whole document. See also PP.render.

≡ ■ Document constants

Any string that doesn't contain '\n' or '\r' characters is considered as an atomic document. For example, '' is an empty document and ' ' is a space.

≡ ■ PP.line ~> doc v1.0.0

PP.line renders as a new line unless undone by PP.group in which case PP.line renders as a space.

For example:

PP.render(20, ['Hello,', PP.line, 'world!'])

PP.render(20, PP.group(['Hello,', PP.line, 'world!']))

≡ ■ PP.lineBreak ~> doc v1.0.0

PP.lineBreak renders as a new line unless undone by PP.group in which case PP.lineBreak renders as empty.

For example:

PP.render(20, ['Lol', PP.lineBreak, 'Bal'])

PP.render(20, PP.group(['Lol', PP.lineBreak, 'Bal']))

≡ ■ PP.softLine ~> doc v1.0.0

PP.softLine renders as a space if the output fits and otherwise as a new line.

For example:

PP.render(
  20,
  PP.intersperse(
    PP.softLine,
    R.split(
      /\s+/,
      'Here is a paragraph of text that we will format to a desired width.'
    )
  )
)

≡ ■ PP.softBreak ~> doc v1.0.0

PP.softBreak renders as empty if the output fits and otherwise as a new line.

For example:

PP.render(10, PP.intersperse(PP.softBreak, R.split(/\b/, 'this.method(rocks)')))

≡ ■ Concatenating documents

An array of documents is considered as a concatenation of documents. For example, [] is an empty document and ['foo', 'bar'] is equivalent to 'foobar'.

≡ ■ PP.append(rhsDoc, lhsDoc) ~> doc v1.0.0

PP.append reverse concatenates the documents.

For example:

PP.render(0, PP.append('bar', 'foo'))

≡ ■ PP.prepend(lhsDoc, rhsDoc) ~> doc v1.0.0

PP.prepend concatenates the documents.

For example:

PP.render(0, PP.prepend('foo', 'bar'))

≡ ■ Lists of documents

≡ ■ PP.intersperse(doc, [...docs]) ~> [...docs] v1.0.0

PP.intersperse puts the given separator document between each document in the given list of documents.

For example:

PP.intersperse(',', ['a', 'b', 'c'])

≡ ■ PP.punctuate(sepDoc, [...docs]) ~> [...docs] v1.0.0

PP.punctuate concatenates the given separator after each document in the given list of documents except the last.

For example:

PP.punctuate(',', ['a', 'b', 'c'])

≡ ■ Lazy documents

≡ ■ PP.lazy(() => doc) ~> doc v1.0.0

PP.lazy creates a lazy document. The given thunk is only invoked as needed to compute the document.

≡ ■ Enclosing documents

≡ ■ PP.enclose([lhsDoc, rhsDoc], doc) ~> doc v1.0.0

PP.enclose encloses the given document between the given pair of documents.

For example:

PP.render(0, PP.enclose(PP.parens, 'foo'))

≡ ■ Document pair constants

≡ ■ PP.angles ~> ['<', '>'] v1.0.0
≡ ■ PP.braces ~> ['{', '}'] v1.0.0
≡ ■ PP.brackets ~> ['[', ']'] v1.0.0
≡ ■ PP.dquotes ~> ['"', '"'] v1.0.0
≡ ■ PP.lineBreaks ~> [PP.lineBreak, PP.lineBreak] v1.1.0
≡ ■ PP.lines ~> [PP.line, PP.line] v1.1.0
≡ ■ PP.parens ~> ['(', ')'] v1.0.0
≡ ■ PP.spaces ~> [' ', ' '] v1.0.0
≡ ■ PP.squotes ~> ["'", "'"] v1.0.0

≡ ■ Alternative documents

≡ ■ PP.choice(wideDoc, narrowDoc) ~> doc v1.0.0

PP.choice(wideDoc, narrowDoc) renders as the given wideDoc on a line if it fits within the maximum width and otherwise as the narrowDoc. PP.lines and PP.lineBreaks within the wideDoc are undone like with PP.group.

For example:

PP.render(5, PP.choice('wide', 'narrow'))

PP.render(3, PP.choice('wide', 'narrow'))

Note that usually the idea is that the narrow version can indeed be rendered more narrowly.

For example:

var hyphen = PP.choice('', ['-', PP.lineBreak])

PP.render(5, PP.intersperse(hyphen, ['hy', 'phen', 'at', 'ed']))

≡ ■ PP.group(doc) ~> doc v1.0.0

PP.group allows PP.lines and PP.lineBreaks within the given document to be undone if the result fits within the maximum width. PP.group(doc) is equivalent to PP.choice(doc, doc).

≡ ■ Nested documents

≡ ■ PP.nest(string | number, doc) ~> doc v1.0.0

PP.nest increases the nesting after next new line by the given string or by the given number of spaces.

For example:

PP.render(6, PP.nest(2, PP.group(PP.intersperse(PP.line, ['foo', 'bar']))))

≡ ■ Layout dependent documents

≡ ■ PP.column(column => doc) ~> doc v1.0.0

PP.column allows a document to depend on the column at which the document starts.

≡ ■ PP.nesting(nesting => doc) ~> doc v1.0.0

PP.nesting allows a document to depend on the nesting after the next new line.

≡ ■ Aligned documents

≡ ■ PP.align(doc) ~> doc v1.0.0

PP.align creates a document such that the nesting of the document is aligned to the current column.

For example:

PP.render(10, PP.group(['foo(', PP.align(['bar,', PP.line, 'baz']), ')']))

≡ ■ PP.hang(string | number, doc) ~> doc v1.0.0

PP.hang creates a document such that the document is nested by the given string or number of spaces starting from the current column.

For example:

PP.render(10, PP.group(['foo(', PP.hang(2, ['bar,', PP.line, 'baz']), ')']))

≡ ■ PP.indent(string | number, doc) ~> doc v1.0.0

PP.indent creates a document such that the document is indented by the given prefix or number of spaces starting from the current column.

PP.render(
  20,
  PP.nest(
    2,
    PP.group([
      'A comment:',
      PP.line,
      PP.line,
      PP.indent(
        '-- ',
        PP.intersperse(
          PP.softLine,
          R.split(/\s+/, 'This is the comment that you are looking for.')
        )
      )
    ])
  )
)


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