BRAT is a functional programming language designed for writing quantum experiments. For an introduction to BRAT, see the extended abstract submitted to PLanQC 2024.

To build BRAT from source, you will need:

• GHC 9.6.4 (can be installed with the ghcup tool)
• The stack build tool for Haskell

Then, navigate to the brat directory and run stack install.

This will add the brat and brat-lsp binaries to ~/.local/bin, and copy configuration for the emacs editor mode to ~/.local/share/brat/.

There is also a plugin for the VS Code editor. To install this, look at vscode/README.md.

By default, the installed brat executable will typecheck a program given as an argument, e.g.:

brat my-program.brat

which, if my-program typechecks, will print out the parsed versions of the declarations and a list of remaining holes.

The --compile flag can be used to compile the BRAT program to the hugr IR and print the JSON representation to the command line.

There is a tool in the root of the repository called hugr_validator (install by cd hugr_validator && cargo install --path .) which is used to check that the JSON output from BRAT constitutes a valid hugr. This is invoked by:

brat --compile my-program.brat | hugr_validator

The brat/examples directory contains some examples of BRAT programs. For example:

• Quantum teleportation: teleportation.brat
• Quantum Fourier transform: teleportation.brat
• Simple Repeat-Until-Success: rus.brat
• Ising Hamiltonian: ising.brat

This directory also contains tests of syntax features which, while terse, may serve as a reference in the short term. For example:

• unified.brat contains some functional programs
• dollar_kind.brat tests polymorphism over kernel types
• tups.brat tests heterogenous lists
• compjuxt.brat, brat/examples/composition.brat contain tests for diagrammatic syntax
• pass.brat tests the 'passthrough' (..) operator
• portpulling.brat demonstrates port pulling