This simple program implements a working blockchain class (based on block mining with a difficulty level) plus a very simple "peer to peer" protocol that enables two or more servers to talk to each other and send/receive their blockchains, based on TCP sockets.

This is a simple project with the following goals, either:

To show newcomers to Common Lisp, an example of how to implement something not so simple but not too complex, like a blockchain, that would involve the use of:

• Cryptography, using ironclad
• Regular expressions, using cl-ppcre
• Sockets, using usocket
• The Common Lisp Object System, specifically the use of generic functions and multiple dispatch, to make the code a bit simpler.

The code is written with as many comments as possible, and is as clear as I can manage to. The aim was not performance, nor production-quality, but educational value.

You can start by taking a look at legochain.lisp and then to peertopeer.lisp

• To show seasoned CL developers who still haven't yet found out what is a blockchain, block mining, and the "nonce" values, a simple answer by looking at the code.

• Add any kind of data to the block's payload. You only need to define the encoding for the payload using conspack:defencoding (see the code)
• Verification of one blockchain against other, rejecting invalid blockchains
• Verification of the continuity (soundness) of each blocks' hash value and sequence value

Peer to peer supported operations:

• Send blockchain to peer
• Request blockchain from peer
• Say "hi" to peer.

You can start many peers from your same machine so you can experiment adding more features to the code.

• Install Portacle, the portable Common Lisp environent.
• Clone this project into the projects subdirectory under the portacle root directory, so you have it into /portacle/projects/legochain.
• Start portacle
• Write (ql:quickload "legochain") to load the program.
• All the functions are in package "legochain".
• Try (legochain::servers-test 9000 9001) to make two blockchain servers talk to each other (a simple demo.)

Flavio Egoavil aka D e f u n k y d r u m m e r

License MIT

I'm always open to pull requests that can make the code more readable or more educational!