Haskell Code Explorer
Haskell Code Explorer is a web application for exploring and understanding Haskell codebases. It provides IDE-like code intelligence features such as types and documentation on hover, "go to definition", "find references" and semantic highlighting.
The public instance of Haskell Code Explorer is available at https://haskell-code-explorer.mfix.io. It contains core libraries (ghc, base, etc.) and a subset of packages from a Stackage snapshot.
Reading and understanding code is an essential part of the software development process. Understanding code in any statically typed language is much easier when code intelligence features (types on hover, go-to-definition, etc.) are available. Code intelligence for Haskell is especially useful because types are informative and precise (thanks to Haskell's purity and global type inference).
Types (actual type, instantiated type, instance resolution tree) and documentation on hover. Types are interactive: left-click on a type constructor -> go to definition, right click on a type constructor -> show kind signature.
Go to definition (cross-package)
git clone https://github.com/alexwl/haskell-code-explorer cd haskell-code-explorer
To build Haskell Code Explorer Stack (https://docs.haskellstack.org/en/stable/README/) is needed.
At the moment Haskell Code Explorer supports GHC 8.6.5, 8.6.4, GHC 8.6.3, GHC 8.4.4, GHC 8.4.3, GHC 8.2.2, and 8.0.2.
For GHC 8.6.5:
For GHC 8.6.4:
stack --stack-yaml=stack-8.6.4.yaml install
For GHC 8.6.3:
stack --stack-yaml=stack-8.6.3.yaml install
For GHC 8.4.4:
stack --stack-yaml=stack-8.4.4.yaml install
For GHC 8.4.3:
stack --stack-yaml=stack-8.4.3.yaml install
For GHC 8.2.2:
stack --stack-yaml=stack-8.2.2.yaml install
For GHC 8.0.2:
stack --stack-yaml=stack-8.0.2.yaml install
Indexing source code of a Cabal package
haskell-code-indexer executable is responsible for indexing packages (by default, the index is saved to
A package should be built using either cabal-install or stack before indexing (
cabal build, or
stack build command should be executed).
The version of GHC used to build
haskell-code-indexer must match the version of GHC used to build a package you are indexing (to find out the version of GHC try
ghc --version or
stack exec ghc -- --version command).
haskell-code-indexer requires globally installed GHC and cabal-install (
cabal). The reason for this is that
cabal-helper library https://hackage.haskell.org/package/cabal-helper to get package build information.
cabal-helper builds (at runtime) an executable linked against a version of Cabal library that was used to configure the package. You may need to run
cabal update to get the latest list of available packages to be able to build the
cabal-helper executable. By default, the
cabal-helper executable (e.g.,
cabal-helper0.8.1.2-Cabal188.8.131.52) is saved to
If there is no globally installed GHC on the system, then it is possible to use
stack exec command (https://docs.haskellstack.org/en/stable/GUIDE/#exec) that adds a path to GHC binaries installed by Stack to
PATH environment variable.
cabal update using stack exec:
stack --resolver=lts-13.20 exec --no-ghc-package-path cabal -- update
Index a package using stack exec:
stack --resolver=lts-13.20 exec --no-ghc-package-path haskell-code-indexer -- INDEXER_OPTIONS
--no-ghc-package-path option unsets
GHC_PACKAGE_PATH environment variable.
cabal fails with the error
Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. if the
GHC_PACKAGE_PATH is set.
Show all indexer options:
haskell-code-indexer --package PATH
Index package with specific
haskell-code-indexer --package PATH --dist dist-newstyle/build/x86_64-linux/ghc-8.2.2/hpath-0.9.2
Starting HTTP Server
haskell-code-server executable reads the package index created by
Show all server options:
Load the indexed package and start the server:
haskell-code-server --package PATH --port 8080
Load multiple indexed packages and start the server:
haskell-code-server --package PATH1 --package PATH2 --package PATH3 --port 8080
Load the indexed package and start the server, use Hoogle API (https://github.com/ndmitchell/hoogle/blob/3dbf68bfd701f942d3af2e6debb74a0a78cd392e/docs/API.md#json-api) to get documentation for functions and types defined in other packages (
haskell-code-server makes requests to https://hoogle.haskell.org/):
haskell-code-server --package PATH --port 8080 --use-hoogle-api
Open http://localhost:8080 in a browser to explore source code of the package.