DaeDaLus

Daedalus is a flexible data description language for generating parsers with data dependencies.

Installing Haskell

Daedalus is implemented in Haskell, so to build it you'd need to setup a Haskell environment. An easy way to get this setup is to use ghcup. You need a Haskell compiler (recommended GHC 9.4.5), and a Haskell package installer (recommended Cabal 3.10).

Building the Daedalus Interpreter

The Daedalus interpreter, called daedalus is a good way to experiment with, and learn the Daedalus language. To build and install the interpreter you may use the command:

cabal install exe:daedalus --installdir=DIR \
                           --overwrite-policy=always

This instructs cabal to build Daedalus and place a link to the binary in directory DIR. The flag --overwrite-policy is optional and instructs cabal to overwite existing links with the same name.

Running the Interpreter

To run daedalus you need a Daedalus specification describing the parser, and a file that should be parsed. For example, you could try the following, assuming daedalus is in your path:

daedalus run tests/midi/midi.ddl --input tests/midi/inputs/moz_k299.midi

The first argument, run, tells the interpreter what to do. The second is a Daedalus specification describing the midi format and the --input flag specfies the input that should be parsed. If the input is parsed successfully, then daedalus will display the resulting semantic value. Otherwise, you should see a parse error describing what went wrong.

Passing --help to daedalus shows all commands, and passing it to a specific command shows the optoins for that command. For more details on the various flags supported by the daedalus tool, have a look at the tool section of the reference manual.

Setting up Your Editor

The directory syntax-highlight contain Daedalus syntax hilighting files for common editors. The README files in syntax-highlight/vscode-daedalus contains instructions on setting up language server support for VS Code.

More about the Daedalus Language

The documentation for Daedalus is not yet complete, but you may read more about the language in the user guide. The formats directory contains numerous small examples of Daedalus specifications. Some starting points are:

• plain-ppm.ddl (PPM image format),
• sexp-mutrec.ddl (S-expressions), and
• midi.ddl (MIDI messages).

Generating C++ Parsers

The daedalus compiler, given a Daedalus format description, can generate a parser in C++ that parses the format. To generate a C++17 parser for a format Main defined in format.ddl, storing the parser in directory parser_dir, run the command

daedalus compile-c++ format.ddl --out-dir=parser_dir

As a result, parser_dir will contain an implementation of the parser, with header file parser_dir/main_parser.h and and procedure implementations in main_parser.cpp.

The entry procedure of the parser will be named parseMain, and has the following parameters:

• an input, of type DDL::Input. In short, a DDL::Input can be constructed from an Array of bytes or a pointer to a null-terminated sequence of characters.
• a reference to a DDL::ParseError, where main_parser.cpp stores its result in the case of an error;
• a reference to a vector of parse results. The class of parse results is declared/defined in main_parser.h / main_parser.cpp, and contains selector methods for accessings its various components.

All classes in the DDL namespace are defined in rts-c/ddl.

The generated parsers require C++17, so to compile them you may need to provide a flag such as std=c++17 to the compiler.

More detail about generating C++ parsers are available in the documentation for the compile-c++ command.

Acknowledgements

This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA) under Contract No. HR0011-19-C-0073. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Defense Advanced Research Projects Agency (DARPA).

The Galois DaeDaLus library includes the following third party components:

• haskell-lzw: copyright 2017 Erik Gunnarsson (https://github.com/egunnarsson/haskell-lzw)