Within the Cardano community there has been a flourishing ecosystem of alternative languages for writing smart contracts. So naturally, one might ask about the differences between these and which they should use for their use case. There is also a big misconception about how writing smart contracts actually works on Cardano. In this document, we'll list some of the main alternatives along with their differences and similarities. Before we get into this though, let's discuss the misconception first so everyone is on the same page.
Cardano uses Haskell for smart contracts
This is not entirely true.
The main Cardano node implementation does indeed happen to be written in Haskell. The virtual machine for executing smart contracts that comes baked into the node is then of course also implemented in Haskell. But that does not mean that it is Haskell itself which is executed by the smart contract virtual machine. Aiken actually has a fully working version of this virtual machine (opens in a new tab) written in Rust.
So what's going on here? What is actually being executed?
Well, there is something called Untyped Plutus Core which is the lowest level representation of a smart contract and it is this low level representation that actually gets executed by the virtual machine. So contrary to popular knowledge, there isn't actually a coupling to Haskell. Armed with this knowledge one may now ask another question:
So what am I writing when I write Plutus?
In the wild, Plutus tends to refer to one of three things:
- Plutus Core, the low-level interpreted code that is executed by the Cardano virtual machine.
- PlutusTx, a Haskell framework that compiles to Plutus Core through the means of a GHC plugin.
- The Plutus Platform, which more broadly includes Plutus Core, PlutusTx and most of the tools developed around Plutus Core.
Most of the time, when people say Plutus, they mean PlutusTx, which has led to a popular belief that Plutus is in fact Haskell.
PlutusTx being built as a GHC plugin means that you even use Haskell tooling like cabal for it. Even so, you are technically not writing Haskell. Code that one writes using PlutusTx is consumed by the plugin and then transformed into Untyped Plutus Core. Essentially, it takes the intermediate representation of Haskell, GHC Core, and turns that into Untyped Plutus Core. This results in not needing to write a new parser and type checker. What you end up with is a kind of embedded language that looks and feels like Haskell but the target runtime is not GHC.
Now that this misconception is out of the way it should be possible to see how other new languages can be created that ultimately compile to Untyped Plutus Core. The current alternatives range from full blown new languages to embedded Domain Specific Languages (abbrev. eDSLs.) Here is a list of the main ones:
- Aiken (opens in a new tab)
- opshin (opens in a new tab)
- Helios (opens in a new tab)
- Plutarch (opens in a new tab)
- plu-ts (opens in a new tab)
- Scalus (opens in a new tab)
The creators of each of these projects all know each other and are in open communication with each other.
Aiken is a brand new language with it's own syntax and compiler. It is not Rust. The compiler happens to be written in Rust but it is not Rust. Not only is Aiken a compiler for a new language but we've also developed everything in such a way that all the libraries we created in Rust are re-usable by people interested in doing more low-level things. One example of this is Lucid (opens in a new tab), which uses Aiken's uplc (opens in a new tab) crate to evaluate transactions before submission to calculate exact redeemer ExUnits without using a node, ogmios, or blockfrost.
As a language, Aiken is purely functional with static typing and type inference. This means most of the time the compiler is smart enough to know what the type of something is without you annotating it. It also let's you make custom types that are similar to records and enums. It does not have higher-kinded types or typeclasses because Aiken aims for simplicity. Writing smart contracts can be tedious, and we therefore believe that a language should remain simple to avoid silly mistakes.
On-chain scripts are typically small in size and scope (relatively, compared to other kind of applications being written nowadays) and, therefore, do not require as much features as general-purpose languages that have to solve much harder problems.
That being said Aiken may introduce more elaborate language features (such as type classes/traits) at a later time if it's found that they are extremely useful to developers.
OpShin allows you to write Smart Contracts in 100% valid but restricted Python3. Since it uses normal Python, you have all the features that come with developing on Python, including widespread editor support, language servers, linters, testing frameworks and verification tools. It implements it's own type system and at compile time checks the types to be correct.
As part of its development, python packages for uplc (opens in a new tab) and pluto (opens in a new tab) have been externalized and are available for anyone that wants to build UPLC tooling in Python (such as optimizers).
As a language, Helios is also purely functional but has limited type inference. It also supports custom types similar to records and enums.
Plutarch is not a new language. You can consider it an eDSL for creating smart contracts with Haskell. In some ways, Plutarch is what PlutusTx should have been. There is no Template Haskell involved.
Since Plutarch is just Haskell, you have everything available to you. Type inference, typeclasses, higher-kinded types, etc.
plu-ts is not a new language. You can consider it an eDSL for creating smart contracts with Typescript. Because of this it's a bit closer to Plutarch conceptually than Aiken or Helios.
It implements it's own type system and at compile time (js runtime) checks the types to be correct.
A Scala implementation of Plutus.
- Untyped Plutus Core (UPLC) data types and functions
- Flat, CBOR, JSON serialization
- CEK UPLC evaluation machine including execution cost calculation
- UPLC parser and pretty printer
- Type safe UPLC expression builder, think of Plutarch
- Macros to generate UPLC code from Scala code, think of PlutusTx but simpler
Only you can decide for yourself which of these fits your needs the best. Each has made some different decisions around design and implementation. Aiken and Helios are on the new language end of the spectrum while Plutarch and plu-ts are on the eDSL end. Plutarch has the most expressive type system while Aiken's types are in between Plutarch and Helios.
Embedded DSLs are nice because they integrate seamlessly with off-chain code and usually allow to reuse existing tools that already work on the host language.
New languages are nice because they include bespoke checks and functionality specifically for Cardano smart contracts directly in their compilers. While they demand a lot of the tooling to be created anew, they also give the opportunity to address shortcomings of existing tooling in various languages.
Which best serves your use case is for you to say. Being the maintainers behind Aiken, we can't be fully partial in providing an unbiaised answer. We encourage you to review the documentation, design decisions and overall project to make an informed decision.