DBL is an interpreter of Fram, an experimental programming language designed around the idea of combining lexically scoped effect handlers with a powerful mechanism of implicit and named parameters in a strongly-typed setting. The main goal of DBL interpreter is providing a tool for bootstrapping Fram compiler. DBL implements core and some of advanced language features, including ML-style parametric polymorphism, rank-N types, mutually recursive data-types and definitions, existential types, and pattern-matching.

DBL is written in pure OCaml and tested with OCaml system version 5.2.0. DBL uses dune as a build system (tested with version 3.17.2).

Simply type dune build to compile the project. If you use opam package manager, you can locally install DBL by typing dune install.

Just type dbl (or rlwrap dbl for better readline support) to run the interpreter in a REPL mode. In this mode you can interactively provide definitions and expressions to evaluate, separated by double semicolon ;;. The example REPL session is shown below.

$ dbl
> let id x = x ;;
> id () ;;
: Unit
= ()
> 

You can also run programs in a batch mode, by providing a file to execute as a command-line argument (e.g., dbl filename.fram).

If you didn't install DBL via dune install (or OPAM, generally) then it's recommended to set the DBL_LIB environmental variable to the lib directory of your local installation of DBL.

Several simple examples can be found in the examples directory. Moreover, in a test/ok directory you can find many tiny examples used to test implementation of various language features.

Source code can be found in the src directory. For a high-level overview of the implementation we encourage to look into the src/Pipeline.ml file and src/Lang directory to see phases and intermediate languages of the interpreter. To run DBL interpreter on all test programs just type ./test.sh dbl test/test_suite. Bugs can be reported on our issue tracker.