HIE files are a new type of file that can be emitted by GHC 8.8 via the -fwrite-ide-info flag. They serialize a bunch of useful information about Haskell source files such as symbol references and type information. This means that it is easy and fast for editors and code intelligence tooling to access information about Haskell programs.

HIE files have already been put to good use, they now power the hyperlinked source functionality in Haddock and are the basis of Haskell’s nascent LSIF support. In the future we want to use them to implement a version of haskell-ide-engine which uses less resources and is more reliable, and reimplement GHCi’s +c command (which is widely used by existing tooling). These implementations in terms of HIE files are hopefully more robust and resillient to the continually changing GHC API.

This talk will be an overview of the contents of HIE files, the kinds of problems that they are well suited to solve, and an introduction to consuming them via the GHC API. We hope to give some inspiration to tooling authors about the kinds of projects they can implement just in terms of HIE files.