The basic task of this library is to parse text as commonmark. Usage example:

{-# LANGUAGE ScopedTypeVariables #-} import Commonmark import Data.Text.IO as TIO import Data.Text.Lazy.IO as TLIO main = do res <- commonmark "stdin" <$> TIO.getContents case res of Left e -> error (show e) Right (html :: Html ()) -> TLIO.putStr $ renderHtml html

The parser is highly polymorphic: in this example, we use the type annotation Html () to indicate that we want it to produce basic HTML without source location attributes. And we return a value in the IO monad. But we could have used a different output format (e.g. Html SourceRange for HTML with source location attributes). And we could have used the Identity monad to get a pure value. (The default parsers work the same way in any monad, but it is possible to define extensions that constrain the monad. For example, an extension for include files might only work in IO, or might have different behavior in IO and Identity.)

Extensibility is emphasized throughout. To change the output for a given format, or support an alternate output format, one has only to define instances of IsBlock and IsInline for a new type. (For an example of this kind of extension, see the commonmark-pandoc package, which defines these instances for pandoc's native types.)

Supporting a new syntactic element generally requires (a) adding a SyntaxSpec for it and (b) defining new type classes. See the examples in the commonmark-extensions package. Note that SyntaxSpec is a Monoid, so one can extend defaultSyntaxSpec by specifying myNewSyntaxSpec <> defaultSyntaxSpec.