Moduleprettyprinter-1.7.1Haskell2010
Prettyprinter.Render.Tutorials.TreeRenderingTutorial
This module shows how to write a custom prettyprinter backend, based on a tree representation of a SimpleDocStream. For a stack machine approach, which may be more suitable for certain output formats, see Prettyprinter.Render.Tutorials.StackMachineTutorial.
Rendering to HTML, particularly using libraries such as blaze-html or lucid, is one important use case of tree-based rendering.
The module is written to be readable top-to-bottom in both Haddock and raw source form.
- 2 types
- 8 values
- Packageprettyprinter-1.7.1
- Exports10
- LanguageHaskell2010
- LicenceBSD-2-Clause
- SourceTreeRenderingTutorial.hs
The type of available markup
2 declarationsFirst, we define a set of valid annotations must be defined, with the goal of
defining a Doc SimpleHtml. We will later define how to convert this to
the output format (Text).
Convenience definitions
The rendering algorithm
3 declarationsWith the annotation definitions out of the way, we can now define a conversion function from SimpleDocStream (annotated with our SimpleHtml) to the tree-shaped SimpleDocTree, which is easily convertible to a HTML/Text representation.
There are two ways to render this; the simpler one is just using
renderSimplyDecorated. However, some output formats require more
complicated functionality, so we explore this explicitly with a simple
example below. An example for something more complicated is e.g. an XHTML
renderer, where a newline may not simply be a newline character followed by a
certain number of spaces, but e.g. involve adding a br/ tag.
To render the HTML, we first convert the SimpleDocStream to the SimpleDocTree format, which makes enveloping sub-documents in markup easier.
This function is the entry main API function of the renderer; as such, it is only glue for the internal functions. This is similar to render from the stack machine tutorial in its purpose.
Render a SimpleDocTree to a Builder; this is the workhorse of the tree-based rendering approach, and equivalent to renderStackMachine in the stack machine rendering tutorial.
Convert a SimpleHtml to a function that encloses a Builder in HTML tags. This is where the translation of style to raw output happens.
Example invocation
0 declarationsWe can now render an example document using our definitions:
:set -XOverloadedStringsimport qualified Data.Text.Lazy.IO as TL:{let go = TL.putStrLn . render . layoutPretty defaultLayoutOptionsin go (vsep [ headline "Example document" , paragraph ("This is a" <+> color Red "paragraph" <> comma) , paragraph ("and" <+> bold "this text is bold.") ]):}<h1>Example document</h1><p>This is a <span style="color: #f00">paragraph</span>,</p><p>and <strong>this text is bold.</strong></p>