{-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE QuasiQuotes #-} module Main (main) where import Prelude hiding (words) import qualified Data.List as L import Data.Text (Text) import qualified Data.Text as T import qualified Data.Text.IO as T import Data.Text.Prettyprint.Doc import Data.Text.Prettyprint.Doc.Render.Text import MultilineTh main :: IO () main = (T.putStrLn . renderStrict . layoutPretty layoutOptions) readmeContents where layoutOptions = LayoutOptions { layoutPageWidth = AvailablePerLine 80 1 } readmeContents :: Doc ann readmeContents = (mconcat . L.intersperse vspace) [ htmlComment "This file was auto-generated by the 'scripts/generate_readme' program." , h1 "A modern Wadler/Leijen Prettyprinter" , vcat [ "[![](https://img.shields.io/travis/quchen/prettyprinter/master.svg?style=flat-square&label=Master%20build)](https://travis-ci.org/quchen/prettyprinter)" , "[![](https://img.shields.io/hackage/v/prettyprinter.svg?style=flat-square&label=Hackage&colorB=0a7bbb)](https://hackage.haskell.org/package/prettyprinter)" , "[![](https://www.stackage.org/package/prettyprinter/badge/lts?style=flat-square&colorB=0a7bbb)](https://www.stackage.org/package/prettyprinter)" , "[![](https://www.stackage.org/package/prettyprinter/badge/nightly?style=flat-square&label=stackage%20nightly&colorB=0a7bbb)](https://www.stackage.org/package/prettyprinter)" ] , h2 "tl;dr" , paragraph [multiline| A prettyprinter/text rendering engine. Easy to use, well-documented, ANSI terminal backend exists, HTML backend is trivial to implement, no name clashes, `Text`-based, extensible. |] , (pretty . T.unlines) [ "```haskell" , "let prettyType = align . sep . zipWith (<+>) (\"::\" : repeat \"->\")" , " prettySig name ty = pretty name <+> prettyType ty" , "in prettySig \"example\" [\"Int\", \"Bool\", \"Char\", \"IO ()\"]" , "```" , "" , "```haskell" , "-- Output for wide enough formats:" , "example :: Int -> Bool -> Char -> IO ()" , "" , "-- Output for narrow formats:" , "example :: Int" , " -> Bool" , " -> Char" , " -> IO ()" , "```" ] , h2 "Longer; want to read" , paragraph [multiline| This package 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 simple document, which can then be rendered to a variety of formats, for example plain `Text`, or Markdown. *What you are reading right now was generated by this library (see `GenerateReadme.hs`).* |] , h2 "Why another prettyprinter?" , paragraph [multiline| Haskell, more specifically Hackage, has a zoo of Wadler/Leijen based prettyprinters already. Each of them addresses a different concern with the classic `wl-pprint` package. This package solves *all* these issues, and then some. |] , h3 "`Text` instead of `String`" , paragraph [multiline| `String` has exactly one use, and that’s showing Hello World in tutorials. For all other uses, `Text` is what people should be using. The prettyprinter uses no `String` definitions anywhere; using a `String` means an immediate conversion to the internal `Text`-based format. |] , h3 "Extensive documentation" , paragraph [multiline| The library is stuffed with runnable examples, showing use cases for the vast majority of exported values. Many things reference related definitions, *everything* comes with at least a sentence explaining its purpose. |] , h3 "No name clashes" , paragraph [multiline| Many prettyprinters use the legacy API of the first Wadler/Leijen prettyprinter, which used e.g. `(<$>)` to separate lines, which clashes with the ubiquitous synonym for `fmap` that’s been in Base for ages. These definitions were either removed or renamed, so there are no name clashes with standard libraries anymore. |] , h3 "Annotation support" , paragraph [multiline| Text is not all letters and newlines. Often, we want to add more information, the simplest kind being some form of styling. An ANSI terminal supports coloring, a web browser a plethora of different formattings. |] , paragraph [multiline| More complex uses of annotations include e.g. adding type annotations for mouse-over hovers when printing a syntax tree, adding URLs to documentation, or adding source locations to show where a certain piece of output comes from. [Idris](https://github.com/idris-lang/Idris-dev) is a project that makes extensive use of such a feature. |] , paragraph [multiline| Special care has been applied to make annotations unobtrusive, so that if you don’t need or care about them there is no overhead, neither in terms of usability nor performance. |] , h3 "Extensible backends" , paragraph [multiline| A document can be rendered in many different ways, for many different clients. There is plain text, there is the ANSI terminal, there is the browser. Each of these speak different languages, and the backend is responsible for the translation to those languages. Backends should be readily available, or easy to implement if a custom solution is desired. |] , paragraph [multiline| As a result, each backend requires only minimal dependencies; if you don’t want to print to an ANSI terminal for example, there is no need to have a dependency on a terminal library. |] , h3 "Performance" , paragraph [multiline| Rendering large documents should be done efficiently, and the library should make it easy to optimize common use cases for the programmer. |] , h3 "Open implementation" , paragraph [multiline| The type of documents is abstract in most of the other Wadler/Leijen prettyprinters, making it hard to impossible to write adaptors from one library to another. The type should be exposed for such purposes so it is possible to write adaptors from library to library, or each of them is doomed to live on its own small island of incompatibility. For this reason, the `Doc` type is fully exposed in a semi-internal module for this specific use case. |] , h2 "The prettyprinter family" , paragraph "The `prettyprinter` family of packages consists of:" , (indent 2 . unorderedList . map paragraph) [ [multiline| `prettyprinter` is the core package. It defines the language to generate nicely laid out documents, which can then be given to renderers to display them in various ways, e.g. HTML, or plain text.|] , [multiline| `prettyprinter-ansi-terminal` provides a renderer suitable for ANSI terminal output including colors (at the cost of a dependency more).|] , [multiline| `prettyprinter-compat-wl-pprint` provides a drop-in compatibility layer for previous users of the `wl-pprint` package. Use it for easy adaption of the new `prettyprinter`, but don't develop anything new with it.|] , [multiline| `prettyprinter-compat-ansi-wl-pprint` is the same, but for previous users of `ansi-wl-pprint`.|] , [multiline| `prettyprinter-compat-annotated-wl-pprint` is the same, but for previous users of `annotated-wl-pprint`.|] , [multiline| `prettyprinter-convert-ansi-wl-pprint` is a *converter*, not a drop-in replacement, for documents generated by `ansi-wl-pprint`. Useful for interfacing with other libraries that use the other format, like Trifecta and Optparse-Applicative. |] ] , h2 "Differences to the old Wadler/Leijen prettyprinters" , paragraph [multiline| The library originally started as a fork of `ansi-wl-pprint` until every line had been touched. The result is still in the same spirit as its predecessors, but modernized to match the current ecosystem and needs. |] , paragraph "The most significant changes are:" , (indent 2 . orderedList . map paragraph) [ [multiline| `(<$>)` is removed as an operator, since it clashes with the common alias for `fmap`. |] , [multiline| All but the essential `<>` and `<+>` operators were removed or replaced by ordinary names. |] , [multiline| Everything extensively documented, with references to other functions and runnable code examples. |] , [multiline| Use of `Text` instead of `String`. |] , [multiline| A `fuse` function to optimize often-used documents before rendering for efficiency. |] , [multiline| SimpleDoc was renamed `SimpleDocStream`, to contrast the new `SimpleDocTree`. |] , [multiline| In the ANSI backend, 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. |] ] , h2 "Historical notes" , paragraph [multiline| This module is based on previous work by Daan Leijen and Max Bolingbroke, who implemented and significantly extended the prettyprinter given by a [paper by Phil Wadler in his 1997 paper »A Prettier Printer«](https://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf), by adding lots of convenience functions, styling, and new functionality. Their package, ansi-wl-pprint is widely used in the Haskell ecosystem, and is at the time of writing maintained by Edward Kmett.|] ] paragraph :: Text -> Doc ann paragraph = align . fillSep . map pretty . T.words vspace :: Doc ann vspace = hardline <> hardline h1 :: Doc ann -> Doc ann h1 x = vspace <> underlineWith "=" x h2 :: Doc ann -> Doc ann h2 x = vspace <> underlineWith "-" x h3 :: Doc ann -> Doc ann h3 x = vspace <> "###" <+> x underlineWith :: Text -> Doc ann -> Doc ann underlineWith symbol x = align (width x (\w -> hardline <> pretty (T.take w (T.replicate w symbol)))) orderedList :: [Doc ann] -> Doc ann orderedList = align . vsep . zipWith (\i x -> pretty i <> dot <+> align x) [1::Int ..] unorderedList :: [Doc ann] -> Doc ann unorderedList = align . vsep . map ("-" <+>) htmlComment :: Doc ann -> Doc ann htmlComment = enclose ""