Zerobook — a tamper-evident, double-entry ledger for Elixir.

Pure-Elixir, zero dependencies. At its core:

• Zerobook.Entry — one line of a transaction (account, integer amount, currency, optional description)
• Zerobook.Transaction — a set of entries that must balance to zero in every currency
• Zerobook.Ledger — an append-only chain of SHA-256 linked blocks that makes any past edit detectable

Quick start

alias Zerobook.{Ledger, Transaction, Entry}

ledger =
  Ledger.new()
  |> Ledger.append!(Transaction.new("txn_1", [
    Entry.new("1000.cash", 10_000, "BRL", "deposit"),
    Entry.new("2000.revenue", -10_000, "BRL")
  ]))
  |> Ledger.append!(Transaction.new("txn_2", [
    Entry.new("3000.expense", 2_500, "BRL", "hosting"),
    Entry.new("1000.cash", -2_500, "BRL")
  ]))

Ledger.verify!(ledger)                    # => :ok
Ledger.balance_of(ledger, "1000.cash", "BRL")  # => 7500

Why integers?

Monetary values are integers to avoid floating point drift. Use the smallest unit of your currency (cents for BRL/USD, attos for crypto, credits as plain integers). It is your job to be consistent.

Tamper evidence

Each block stores the SHA-256 of its content plus the hash of the previous block. Zerobook.Ledger.verify/1 recomputes every link; any change to a past transaction, or any reordering/insertion/deletion, breaks the chain and is reported with the offending block index.

Ledger state is plain immutable data (blocks are structs with prev_hash and hash fields), so persistence is trivial: store blocks in SQLite, Postgres (jsonb) or ETS and rebuild the ledger by appending them in order.