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Sep 23, 2021

Cardano Ledger

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This repository contains the formal specifications, executable models, and implementations of the Cardano Ledger.

The documents are built in our CI and can be readily accessed using the following links:

Era Design Documents Formal Specification CDDL
Byron Chain Spec, Ledger Spec CDDL
Shelley Design Spec CDDL
Allegra & Mary Multi-Currency, UTXOma Spec CDDL
Alonzo eUTXO Spec CDDL

Other Documents:

In addition, there is a formalization of the Ledger Specification in Isabelle/HOL which can be found here.

Repository structure

The directory structure of this repository is as follows:

Build tools

For building LaTeX documents we use nix. Haskell files can be built either with nix or cabal.

When using nix it is recommended that you setup the cache, so that it can reuse built artifacts, reducing the compilation times dramatically:

If you are using NixOS add the snippet below to your /etc/nixos/configuration.nix:

nix.binaryCaches = [

nix.binaryCachePublicKeys = [

If you are using the nix package manager next to another operating system put the following in /etc/nix/nix.conf if you have a system-wide nix installation , or in ~/.config/nix/nix.conf if you have a local installation:

substituters        =
trusted-public-keys =

Building the LaTeX documents and executable specifications

When using nix the documents and Haskell code can be readily built by running:

nix build

The LaTeX documents will be places inside directories named result*, e.g.:


Building individual LaTeX documents

Change to the latex directory where the latex document is (e.g. eras/shelley/formal-spec for the ledger specification corresponding to the Shelley release, or eras/byron/ledger/formal-spec for the ledger specification corresponding to the Byron release). Then, build the latex document by running:

nix-shell --pure --run make

For a continuous compilation of the LaTeX file run:

nix-shell --pure --run "make watch"


While building most compilation warnings will be turned into an error due to -Werror flag. However during development it might be a bit inconvenient thus can be disabled on per project basis:

cabal configure <package-name> --ghc-options="-Wwarn"
cabal build <package-name>

Testing the Haskell programs

The tests can be run with cabal. For example the Shelley tests can be run with:

cabal test cardano-ledger-shelley-test

Note that the tests in cardano-ledger-shelley-test require two Ruby gems, cbor-diag and cddl.

It can be helpful to use the --test-show-details=streaming option for seeing the output of the tests while they run:

cabal test cardano-ledger-shelley-test --test-show-details=streaming

Running Specific Tests

The test suites use Tasty, which allows for running specific tests. This is done by passing the -p flag to the test program, followed by an awk pattern. You can alternatively use the TASTY_PATTERN environment variable with a pattern. For example, the Shelley golden tests can be run with:

cabal test cardano-ledger-shelley-test --test-options="-p golden"


TASTY_PATTERN=golden cabal test cardano-ledger-shelley-test

Tasty allows for more complex patterns. For instance, to run only the Byron update mechanism tests for the ledger that classify traces, we can pass the -p $1 ~ /Ledger/ && $2 ~ /Update/ && $3 ~ /classified/ option. Here each $i refers to a level in the tests names hierarchy. Passing -l to tasty will list the available test names.

When testing using cabal, pay special attention to escaping the right symbols, e.g.:

cabal test byron-spec-ledger:test:byron-spec-ledger-test --test-options "-p \"\$1 ~ /Ledger/ && \$2 ~ /Update/ && \$3 ~ /classified/\""

Replaying QuickCheck Failures

When a QuickCheck test fails, the seed which produced the failure is reported. The failure can be replayed with:

cabal test cardano-ledger-shelley-test --test-options "--quickcheck-replay=42"

(where 42 is an example seed).

Test Scenarios

Most of the test suites are grouped into test scenarios. For example, the Shelley test suite contains ContinuousIntegration, Development, Nightly, and Fast, which can be run with the --scenario flag. For example:

cabal test cardano-ledger-shelley-test --test-options --scenario=Fast


We have support for running ghcid from inside of nix-shell. Enter nix-shell from the base directory of the repository, change directories to the cabal package that you wish to check, then run ghcid.

For example:

cd eras/shelley/impl/

nix-build Infrastructure

The artifacts in this repository can be built and tested using nix. This is additionally used by the Hydra CI to test building, including cross-compilation for other systems.

To add a new Haskell project

To add a new Haskell project, you should do the following:

  1. Create the project in the usual way. It should have an appropriate .cabal file.
  2. Add the project to the top-level stack.yaml, configuring dependencies etc as needed. If your project's configuration deviates too far from the snapshot in ``cardano-prelude`, then you may have to submit a PR there to update that snapshot.
  3. At this point, test that your new project builds using stack build <project_name>.
  4. Run nix-shell ./nix -A iohkNix.stack-cabal-sync-shell --run scripts/ script to check and report your change from stack.yaml to cabal.project.
  5. Run the regenerate script to update sha256 checksums in cabal.project.
  6. Test that you can build your new project by running the following: nix build -f default.nix libs.<project_name>. If you have executables, then you may also try building these using the exes.<executable_name> attribute path. A good way to see what's available is to execute :l default.nix in nix repl. This will allow you to explore the potential attribute names.
  7. If you want your product to be tested by CI, add it to release.nix using the format specified in that file.

To add a new LaTeX specification

To add a new LaTeX specification, the easiest way is to copy from one of the existing specifications. You will want the Makefile and default.nix (say from the Shelley ledger spec).

  1. Copy these files into the root of your new LaTeX specification.
  2. Modify the DOCNAME in the Makefile.
  3. Update default.nix to:
    1. Make sure that the relative path in the first line is pointing to (default.nix)[./default.nix]. This is used to pin the nixpkgs version used to build the LaTeX specifications.
    2. Update the buildInputs to add in any LaTeX packages you need in your document, and remove any unneeded ones.
    3. Alter the meta description field to reflect the nature of this document.
  4. Add a link to the package at the bottom of default.nix, following the existing examples.
  5. To require that your specification be built in CI, add it at the end of the list in default.nix following the existing examples.

Additional documentation

You can find additional documentation on the nix infrastructure used in this repo in the following places:

Note that the user guide linked above is incomplete and does not correctly refer to projects built using iohk-nix, as this one is. A certain amount of trial and error may be required to make substantive changes!


Code formatting

We use editorconfig to ensure consistency in the format of our Haskell code. There are editorconfig plugins for several text editors, so make sure that your editor honors the configuration in .editorconfig.

Additionally, we use ormolu for formatting. There is a script here which uses nix to format the appropriate directories.