Correct by Construction Programming in Agda

Agda tutorial at POPL 2019


In a dependently typed programming language you can get much stronger static guarantees about the correctness of your program than in most other languages. At the same time, dependent types enable new forms of interactive programming, by letting the types guide the construction of the program. Dependently typed languages have existed for many years, but only recently have they become usable for practical programming.

In this tutorial, you will learn how to write correct-by-construction programs in the dependently typed programming language Agda. Concretely, we will together implement a verified typechecker and interpreter for a small C-like imperative language. Along the way, We will explore several modern features of the Agda language that make this task more pleasant, such as dependent pattern matching, monads and do-notation, coinduction and copattern matching, instance arguments, sized types, and the Haskell FFI.


For the exercises in this tutorial, you need to install Agda or later, the Agda standard library v0.17 or later, and the BNFC tool. There is a bash script that installs all of these on a fresh installation of Ubuntu 18.04 or later. Alternatively, here are step-by-step instructions:

First, make sure you have git, cabal, and emacs installed. You also need the zlib c library. On Ubuntu and related systems, the following command should work:

sudo apt-get install git cabal-install emacs zlib1g-dev

Make sure that binaries installed by cabal are available on your path by adding the following line to ~/.profile:

export PATH="$PATH:$HOME/.cabal/bin"

To install Agda and its prerequisites:

cabal update
cabal install alex happy
cabal get Agda && cd Agda- && cabal install
agda-mode setup

To install the Agda standard library:

git clone
cd agda-stdlib && git checkout v0.17 && cabal install
mkdir $HOME/.agda
echo $PWD/standard-library.agda-lib >> $HOME/.agda/libraries
echo standard-library >> $HOME/.agda/defaults
cd ..

To install BNFC:

cabal install BNFC