Aim

We would like pandoc to be fully extensible with Lua.

Ideas

Exposing http-client to Lua

When working with scientific documents, it is often convenient to be able to look up author informations (given some ID) automatically, for example via ORCID. It is therefore necessary for pandoc to have a http client subsystem. http-client is a popular library for writing http clients in Haskell and thus a good choice for implementing a http client subsytem in pandoc and to expose its functions to Lua.

Technical Details

We rely on hslua, which provides bindings between Lua and Haskell, to expose Haskell functions to Lua. Exposing Haskell functions to Lua amounts to making them an instance of ToHaskellFunction typeclass, with the following instances

ToHaskellFunction HaskellFunction
Pushable a => ToHaskellFunction (Lua a)
(Peekable a, ToHaskellFunction b) => ToHaskellFunction (a -> b)

• HaskellFunction is the type of Haskell functions that can be called from Lua. It is actually an alias for Lua NumResults, where Lua represents a Lua computation and NumResults is the number of results of that Lua computation.
• Pushable is the type of values that can be pushed into the Lua stack.
• Peekable represents the type of values that can be read from the Lua stack.