Hop

Introduction

Hop is a stack-machine-based byte-code interpreter. Hop is intended to be both fast and customizable, aiming to be a target for higher-level interpreted programming languages.

Stack machine interpreters differ from more traditional register-based interpreters in that they do not use registers for passing arguments to instructions. Instructions execute by pushing and popping values from the top of a stack.

Perhaps the most distinguishing feature of Hop over other stack-machine interpreters is that Hop does not have a fixed instruction set. Rather, users are expected to define their own instructions that are best suited to their use case. Hop provides common instructions which one can, but is not required to, use in their instruction set.

Tutorials and Examples

• Examples can be found in the examples directory, though there are not many examples yet.
• We do not yet have a tutorial, though it is on our radar. For now, reading examples and the source code are your best bet for learning how to use these libraries.

Building from Source

Hop is a collection of C++23 libraries, and relies heavily on Bazel for building and testing. You will need a C++23-compliant compiler and a relatively recent copy of Bazel. Specifically,

• Bazel version 5.4.0 or greater
• Clang 14.0.0

Hop libraries is intended to be used from your C++ code and always built from source. For this reason, Hop does not have any installation or setup process. If you would like to download and play around with the examples, they can be built via these commands:

$ git clone https://github.com/asoffer/hop.git
$ cd hop
$ bazel build -c opt //examples:fibonacci

If you would like to include Hop in your own Bazel based project, you can use an http_archive rule in your WORKSPACE file. See Bazel's tutorials for how to do this. A good starting point will be to copy this into your WORKSPACE file:

http_archive(
  name = "hop",
  urls = ["https://github.com/asoffer/hop/archive/<<hash>>.zip"],
  strip_prefix = "hop-<<hash>>",
  sha256 = "<<sha>>",
)

where <<hash>> and <sha>> are replaced with the appropriate Git hash and checksum as desired.

Compilation may also be configured via the //hop/configuration flag, which may be specified as "debug", "harden", or "optimize". These flags are can be specified orthogonally to Bazel's -c opt, -c fastbuild, or -c dbg. Hardened builds will insert relatively cheap debuggung assertions. Debug builds will insert even more expensive checks, possibly modifying data structures to track more debugging information.

Continuous Integration

Currently Hop is only tested on Ubuntu-like platforms. We are open (in fact, ecstatic) to receive pull requests that support more environments and platforms (new hardware, operating systems, compilers, etc). However, we are unlikely to prioritize support for anything other than the few most-recent versions of any particular operating system or compiler.