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June 15, 2021 16:48
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Mission: Combining Prolog, blockchain and cryptocurrency.

"Prolog was the beginning. Epilog is the end."

Latest Epilog binaries (automatically updated)

How to build from source

Go to some directory:

> git clone
> git clone
> [install C++ Boost, 1.62 or later]
> cd epilog
> make all

How to run

In two separate terminal windows do:

> bin/epilogd --name foo --port 8701 --interactive
> bin/epilogd --name bar --port 8702 --interactive

(You can launch multiple engines on the same machine on different ports.)

There are some special commands and operators:

List current connections:

?- connections.

Add another epilogd to your address book:

?- add_address('', 8702).

(It'll get connected within a minute.)

?- member(X, [1,2,3,4]) @ bar.

Run the goal "member(X, [1,2,3,4])" on the node 'bar'. (Requires a connection to the node 'bar'.)

Use the regular 'halt/0' predicate to quit (interactive) epilogd:

?- halt.

For fun you can actually create compatible bitcoin keys with epilogd:

?- privkey(NewKey), pubkey(NewKey,PubKey), address(PubKey, Addr), bc1(PubKey,BC1).            
NewKey = 58'KxT19dNhBFbtm4kQgzSoTf6CBnoTyqsWAm2avZ9HrT6nxfQx8HU6,
PubKey = 58'1qPpPqtGiSy9AZ4rVuTRC5N2Pz2ynGbjejq2Zr2iYriei,
Addr = 58'1CvaN5tzcpowy2swPGrsjyhh6eyH5PnaA6,
BC1 = "bc1qst950vj87th6fs62gjfepxpytj7p9u6tkq08jj".

What is Prolog?

Prolog is a language based on predicates (= "program") and terms (= "data structures.") Predicates become logical axioms for which you can ask queries: "Solve X,Y,Z such as p(X,Y,Z) is true." It turns out that this system is Turing machine complete, and yes although it means you can create Pacman in Prolog, it is more useful for solving other problems.

Why Prolog?

Prolog is a Turing machine complete database based on predicate logic, a branch in mathematics. It's a very high level language; complicated things can be succintly expressed and solved. Some key features are:

  • Code in Prolog has the same representation as data.
  • Cryptocurrency is about maintaining a consistent state.
  • Logic helps in smart contracts.
  • Immutable datastructures. Fits nicely with the "blockchain paradigm."
  • Binding variables = spending.
  • Frozen closures are mapped to UTXO spending and smart contracts execution.
  • Pragmatic. Although based on its mathematical foundation it's also pragmatic.
  • ...

What is Epilog?

(First study Prolog, then...)

Imagine that you have a Prolog session:

?- <type something here>

Imagine that the whole world shares this prompt. You type something and it gets concatenated to a never ending query with everybody elses typing. Each goal gets incrementally solved. Miners bundle the queries together in chunks (blocks.) No one really hits "enter," or "enter" is continually being pressed between blocks, but the state persists. You are only allowed to append to the neverending query as long it does not fail which should remind you about the definition of logical consistency in mathematics. This is basically it. This is the "operating system" that underpins everything.

In this operating system there's also a scarce resource. As Prolog is fully programmable you can define arbitrary rules on how this scarce resource should be exchanged between parties. You can also maintain states via logic variables which enhance the expressiveness of smart contracts. Prolog is also very succint which means that smart contracts become compact and keeping things compact means increased scalability.

Money supply and premine

The total supply is 4,242,424,242,424,242 EPS, that's 42 eight times. The genesis block reward goes to the founders (aka premine) which is 42,445,243,724,242 EPS (~ 1%.) The remaining reward is 21000000000 >> (height / 100000) with the same block interval as bitcoin (10 minutes.) Inflation tapers twice as fast as bitcoin, or a halving event every other year. Last reward will be in block 3,500,000.


Epilog is written in C++. It contains a complete Prolog implementation with extensions. We've struggled hard to achieve a minimum number of external dependencies: only boost and libsecp256k1 (from bitcoin.) This is intentional as it becomes less fragile for full node validation; consensus programming is highly non-trivial. Like bitcoin, our goal is to never use hard forks. Hard forks means centralization as it gives the impression that "developers are in control." We think nobody should be in control.

If you're a Prolog expert and knows C++ and want to get involved in this exciting project, then drop an email at below. I'm in the process of assembling an international team. Let's compete with everything but bitcoin.





Epilog = Prolog + Blockchain + Cryptocurrency







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