Skip to content
Units of measure as a GHC typechecker plugin
Haskell Dhall Nix Shell
Branch: master
Clone or download

Units of measure as a GHC typechecker plugin

The uom-plugin library adds support for units of measure to GHC using the new experimental facility for typechecker plugins, which is available in GHC 7.10 and later. See Data.UnitsOfMeasure.Tutorial for an introduction to the library, and the accompanying paper for more background. An example of a package that uses the library is given in uom-plugin-examples.

The library has been tested with GHC 7.10.3, 8.0.2 & 8.2.2.

⚠️ Please don't use this plugin with later versions of GHC as it will likely fail to solve constraints, #43.


Grab the source.

> git clone
> cd uom-plugin

Then build and run with any of these methods:

  • With Cabal new-build

> cabal new-build all
> cabal new-exec Examples
  • With Nix and Cabal

The default compiler is set in ./nix/config.nix as compiler ? "ghc822";

> nix-shell

[nix-shell:]$ cabal new-build all
Resolving dependencies...
Up to date

With GHC > 8.2.2 only the plugin itself builds, not its tests or the examples. There are conditionals for this in the package.dhall files;

# package.dhall
    when = { condition = "impl(ghc > 8.2.2)", buildable = False }

# .cabal
    if impl(ghc > 8.2.2)
      buildable: False

If the conditions were not in place then what they do is equivalent to;

> nix-shell -p haskell.compiler.ghc822 -p haskell.packages.ghc822.cabal-install

[nix-shell:]$ cabal new-build uom-plugin --disable-tests
Resolving dependencies...
Build profile: -w ghc-8.2.2 -O1
  • Within a Cabal Sandbox

> cabal sandbox init
(cd uom-plugin && cabal sandbox init --sandbox=../.cabal-sandbox && cabal install)
> cd uom-plugin-examples/
uom-plugin-examples> cabal sandbox init --sandbox=../.cabal-sandbox
uom-plugin-examples> cabal build
uom-plugin-examples> dist/build/Examples/Examples
  • With Stack

From the set of stack-<ghc-version>.yaml provided files, picking the one that corresponds to ghc-8.2.2;

> stack build --stack-yaml=stack-8.2.2.yaml
> stack exec Examples --stack-yaml=stack-8.2.2.yaml

Continuous Integration

Build Status

If installing tooling from the master branch of haskell-ci then generate the .travis.yml setup with;

> make-travis-yml --output=.travis.yml --config=cabal.haskell-ci cabal.project

If installing tooling from the package branch of haskell-ci then generate the .travis.yml setup with;

> haskell-ci --output=.travis.yml --config=cabal.haskell-ci cabal.project
You can’t perform that action at this time.