Awesome

comby

See the usage documentation.

A short example below shows how comby simplifies matching and rewriting compared to regex approaches like sed.

<details> <summary>Comby supports interactive review mode (click here to see it in action).</summary>

</details>

Install (pre-built binaries)

Mac OS X

brew install comby

Ubuntu Linux

bash <(curl -sL get-comby.netlify.app)
Other Linux distributions: The PCRE library is dynamically linked in the Ubuntu binary. For other distributions like Arch Linux, a fixup is needed: sudo ln -s /usr/lib/libpcre.so /usr/lib/libpcre.so.3. On Fedora, use sudo ln -s /usr/lib64/libpcre.so /usr/lib64/libpcre.so.3. Alternatively, consider building from source.

Windows

Install the Windows Subsystem for Linux and install Ubuntu. Then run bash <(curl -sL get.comby.dev)

Docker

docker pull comby/comby

<details> <summary>click to expand an example invocation for the docker image</summary>

Running with docker on stdin:

docker run -a stdin -a stdout -a stderr -i comby/comby '(:[emoji] hi)' 'bye :[emoji]' lisp -stdin <<< '(👋 hi)'

Isn't a regex approach like sed good enough?

Sometimes, yes. But often, small changes and refactorings are complicated by nested expressions, comments, or strings. Consider the following C-like snippet. Say the challenge is to rewrite the two if conditions to the value 1. Can you write a regular expression that matches the contents of the two if condition expressions, and only those two? Feel free to share your pattern with @rvtond on Twitter.

if (fgets(line, 128, file_pointer) == Null) // 1) if (...) returns 0
      return 0;
...
if (scanf("%d) %d", &x, &y) == 2) // 2) if (scanf("%d) %d", &x, &y) == 2) returns 0
      return 0;

To match these with comby, all you need to write is if (:[condition]), and specify one flag that this language is C-like. The replacement is if (1). See the live example.

Build from source

Install opam. TL;DR do sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh)
Run this if you don't have OCaml installed (it bootstraps the OCaml compiler):

opam init
opam switch create 4.11.0 4.11.0

Run eval $(opam env)
Install OS dependencies:
- Linux: sudo apt-get install autoconf libpcre3-dev pkg-config zlib1g-dev m4 libgmp-dev libev4 libsqlite3-dev
- Mac: brew install pkg-config gmp pcre libev
Then install the library dependencies:

git clone https://github.com/comby-tools/comby
cd comby 
opam install . --deps-only

Build and test

make
make test

Install comby on your PATH by running

make install