Functional programming is an ideal fit for developing blockchains

There are a lot of blockchains on the market, however solely a handful of unbiased implementations exist. Tezos is one in every of them, and as an early architect of the chain, I had the possibility of being concerned in its creation and improvement from the start. An early, and fortuitous choice was to observe the useful programming paradigm to construct the chain, utilizing the OCaml programming language. All through this expertise, I discovered that useful programming and blockchains had been an excellent match for one another. Let’s try to see why!


From the beginning, it was clear that safety needs to be on the heart of technical design selections. Blockchains and cryptocurrencies current an nearly worst case surroundings for bugs:

  • Vital bugs can’t be mentioned overtly as a result of they have an effect on dwell methods, however they should be deployed concurrently throughout many members with out using a trusted third occasion. This leaves only a few choices to deal with them, moreover covert bug fixes.
  • There are massive and direct monetary incentives for felony hackers to find bugs in these methods since they safe actual monetary worth.

Whereas safety is crucial, there’s sadly no surefire manner to make sure it. Even essentially the most rigorous approaches like formal verification stay costly and are topic to bugs within the specs themselves. Some technical selections nonetheless can assist.

A serious cause for choosing OCaml as a programming language was that it may assist eradicate massive lessons of bugs. As a reminiscence managed language, there is no such thing as a want to fret about buffer overflows as an illustration, however this solely scratches the floor. Tezos leverages OCaml’s very robust static sort system to implement isolation and permissions. The code managing a transaction can not entry the underlying storage of the ledger; it can not even assemble the categories it might want to jot down to the storage. As an alternative, the sort system constrains it to jot down to a better abstraction that may examine and sanitize each motion. Encapsulation just isn’t distinctive to useful programming after all, however the module signature mechanism of OCaml makes it very easy to overview and refine permissions.

The Tezos protocol embeds an interpreter for Michelson, the digital machine behind Tezos sensible contracts, which is itself statically typed and useful. That interpreter leverages OCaml’s GADT system to make sure that mistyped Michelson contracts can not even be constructed. That is one other good safety property that we inherit from the language itself.

An outdated adage claims that if a program is written in a useful programming language, then it really works. The assertion is after all flippant, although I do do not forget that the very first model of Tezos that compiled, after months of improvement, did run on the primary try to was in a position to course of transactions.

None of those properties can assure safety, however they care for extra apparent flaws, liberating up programmers and safety researchers to give attention to higher-level issues.

If the gold commonplace is formal verification, then OCaml is extraordinarily effectively positioned. Coq, a number one interactive theorem prover and proof checker is written in OCaml and may naturally output OCaml. As well as, Coq-of-OCaml can do the reverse and put together Coq code from present OCaml code.

Blockchains appear to be a useful programming drawback

As Tezos started taking form, I spotted that lots of the issues that should be solved when implementing a blockchain are just like the kind of issues useful programmers are very conversant in. At its coronary heart, a blockchain is a approach to characterize a mutable state utilizing an append-only information construction. The state is what you get once you maintain over the blocks with an accumulator. That is typical of how we deal with information and their immutability within the useful world. 

One drawback useful programming may be very appropriate for is dealing with chain reorganizations, when blocks which have been utilized to the state should be rolled again as a result of a distinct department finally ends up being chosen by the consensus. When the info is saved as a useful tree, community members can undo the impact of those blocks on the state effectively. Then, because the chain progresses, it’s good to clear it up and free the reminiscence with a rubbish collector, which is once more one thing that may be very acquainted on the planet of useful programming.

Moreover, when you’re constructing sensible contracts, then you definately want a sensible contract language, which implies you’ll want a compiler—compilers are typically dealt with very effectively by useful programming generally and OCaml specifically. There are a whole lot of steps when compiling from a supply language to a goal language: lexically parsing the textual content to create particular person tokens, assembling these into an summary syntax tree, and reworking varied components of that tree till we get to the goal language, typically going by plenty of intermediate representations, the place the sort system constrains the transformations. The code for all these steps will be very elegant and environment friendly when written in OCaml.

The compiled sensible contract, too, advantages from being written in a useful fashion. Every contract has its personal immutable information related to it, so you can’t have or not it’s a pure perform. What we will do nonetheless is load that storage and the contract into an remoted digital machine to execute. It’s the following smartest thing to a pure perform, deterministic and unaffected by exterior values.

Why OCaml?

OCaml just isn’t an apparent alternative. As a programming language, it stays considerably area of interest. Nonetheless, it’s a mature language that provides the safety of a strongly-typed useful programming language, with out compromising on efficiency. Its roots are in French academia, and it’s utilized by corporations like Fb, Jane Avenue Capital, and Docker in security-sensitive initiatives. It’s also a preferred language for writing compilers. You’ll be able to write very readable, dependable, and environment friendly code in OCaml, and whereas it doesn’t forestall outright programming errors, the robust type-system and the absence of negative effects introduced by useful programming assist provide you with excessive confidence within the correctness of your code.

Haskell, a extra widespread useful programming language presents a really pure paradigm based mostly on lazy analysis, however it’s more durable to jot down Haskell code that’s each performant and idiomatic.

A typical objection is that utilizing an unusual programming language like OCaml makes it more durable to rent programmers. That argument may maintain some weight for corporations making an attempt to recruit many 1000’s of builders, nevertheless it was obvious early on that the best measurement for a core protocol improvement crew is far smaller than that. As well as, I discovered that builders with a knack for constructing most of these methods had no problem choosing up the language in a matter of months.

I used to be impressed early on by WhatsApp’s means to scale to lots of of hundreds of thousands of customers with a small, centered crew of Erlang builders, and I might say that this inspiration stood the take a look at of time.

Whereas OCaml is used for the very foundations of Tezos, the group of builders that builds instruments and functions round it sometimes achieve this in all kinds of widespread languages. Equally, for writing sensible contracts, there are high-level languages that provide you with a Python-like or a JavaScript-like expertise, to say some examples.


In conclusion, there’s a very pure match between blockchains and useful programming and it might be a disgrace to not use the best software for the best job! There are quite a few issues but to be solved and alternatives for builders all over the place to use their abilities to construct higher instruments, functions and infrastructure for this nascent (however booming) class. For those who’re to study extra about blockchain and Tezos, head over to and be part of the rising group of builders within the ecosystem.

Tags: blockchain, functional programming, OCaml, partnercontent

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