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How to Install

This sections documents how to install LH and its dependencies.

External Software Requirements

In order to use LiquidHaskell, you will need a SMT solver installed on your system. Download and install at least one of:

Note: The SMT solver binary should be on your PATH; LiquidHaskell will execute it as a child process.

Installing LiquidHaskell

LiquidHaskell itself is installed&enabled by adding it as a dependency in your project's .cabal file.

Depending on your version of GHC, you might want to use a build of LiquidHaskell from github or from Hackage.

  • ghc-9.2.5: use LiquidHaskell from github
  • ghc-9.0.2: use liquidhaskell-0.9.0.2.1 and liquid-base-0.4.15.1.0 from Hackage
  • ghc-8.10.7: use liquidhaskell-0.8.10.7 and liquid-base-0.4.15.0.0 from Hackage

Newer versions of GHC aren't supported yet.

When using liquidhaskell from github, add liquidhaskell to the build-depends section of your .cabal file, and configure stack or cabal-install to look for the package there. The following section points to an example project that does this.

When using liquidhaskell from Hackage, add liquidhaskell and liquid-base to the build-depends section of your .cabal file, as you would any other dependency.

This causes stack (or cabal) to automatically:

  1. Install LiquidHaskell
  2. Tell GHC to use LH during compilation
  3. Display liquid type errors during compilation
  4. Integrate LH with ghci, ghcid and all GHC compatible tooling for your favorite editor.

Examples

The following concrete examples show the LiquidHaskell plugin in action:

You can use the .cabal, stack.yaml and cabal.project files in the sample packages to see how to write the equivalent files for your own codebase.

Liquid Dependencies

If you project depends on some well known library package foo (e.g. base or vector), then it's likely that the LiquidHaskell developers have written some specs for it. For boot libraries, that is those comming with the compiler, they are provided without further configuration. For other libraries like vector, a package like liquid-vector needs to be added to your build-depends.

In order to see what specs are used for boot libraries, you can check the modules in src.

For the vector library, you can find the specs here.

In general, whenever your module imports another module A.B.C, Liquid Haskell will look for additional specs in any module of packages in build-depends with name A.B.C_LHAssumptions.

Editor Integration

Since LiquidHaskell is implemented as a GHC plugin, you get to automatically reuse all ghc-based support for your editor as is. The sample packages include examples for vscode, vim and emacs.

Uninstallation

Just remove the liquid packages from your build-depends again, and GHC won't use LiquidHaskell anymore. You may also want to delete the .liquid directories placed alongside your source files (they contain debug information).

Other Options

Online Demo: For small projects without a .cabal file, you can paste your code into the online demo.