This is a short and non-technical blog post demonstrating why
programming language is a good choice for building
Cryptocurrencies are not your average software
Cryptocurrencies are different from other programs in one key
way: One mistake in the code can result in the instantaneous loss
of all value of all users.
This is not often the case with other software. In conventional
applications and services, mistakes in the code lead to downtime,
unsatisfied users, or a successful hack of the service provider.
Only in the rarest cases does this mean the complete and permanent
destruction of the service and all invested money being gone for
good. Recovery is usually possible for ordinary business software.
In cryptocurrencies code is money, so extra caution is
needed when writing it.
While other financial software also needs lots of caution,
mistakes in cryptocurrencies can be especially severe due to their
decentralised nature. Traditional banking has safety mechanisms
like chargebacks and contracts between banks that make it possible
to undo transactions correct mistakes after they happened. In
cryptocurrencies, money that's gone is usually gone for good.
Avoiding mistakes through good tooling
How do you avoid mistakes in your code? One way is to hire
excellent programmers. However, all programmers are humans and they
will eventually make mistakes. It's safer to have human-written
code cross-checked by a machine to the fullest extent possible. It
is crucial to use a programming language that makes mandatory
automated checks easy to write.
Haskell is a programming language that was designed for safety.
Haskell provides hard guarantees that certain kinds of
mistakes cannot be in the code. How does it do this? Let's look at
some features that make this possible.
Haskell safety features
Memory safety. This means that you cannot
accidentally modify values in your computer's memory that you did
not intend to modify. Haskell prevents mistakes where garbage data
is written into memory and the program is exhibiting arbitrary
behaviour from that point. It also makes one of the most dangerous
security vulnerabilities, remote code execution by an
Static types.. Haskell enforces that the
operations you do with your data are sound. Any function that
processes data must declare what types of data (such as
numbers, user names, cryptographic hashes) are consumed or produced
by it. When you try to feed a function data of the wrong type
Haskell will complain and refuse to build your code. This means the
problem is detected long before the code ever ships, and in fact
it's impossible to ship the code until the mistake is
corrected. The types of all things being explicitly clear also
makes it easier to understand the code. The ease of understanding
enables programmers on your team to work faster and makes the job
of external experts easier.
Purity. Purity is the ability to prove the
absence of unwanted side-effects. In Haskell you can
indicate (usually done with the
IO type) whether a
function in the code has any interaction with the outside world. If
you indicate that code doesn't interact with the outside world,
Haskell guarantees that it will not do so. If a function
with the type
checkSufficientBalanceForTransaction :: User
-> Amount -> Result does not carry an
label you know it cannot access the Internet, that it cannot read
any files, and that it cannot by itself have any visible effect on
the world. You are guaranteed that all it can do is access the data
that is passed in (the
User whose balance is to be
checked, and the
Amount the user would like to send)
and return a
Result that says whether the user's
balance is sufficient. This dramatically reduces the amount of code
you have to vet against malicious inputs. Pure functions are
guaranteed to always return the same output value given the same
input values. This property allows the Haskell compiler to produce
programs that run faster and use all available CPU cores. It also
eases testing and quality assurance.
Haskell forces you to write code that is explicit, covers all corner cases, and is hard
Benefits of the Haskell ecosystem
Raw technical features are not the only reason why Haskell is
becoming popular for writing cryptocurrencies. It is also the
ecosystem that surrounds the language, and the mind set of Haskell
programmers that make it an attractive choice.
Quality focused community
Haskell tends to select for engineers who are particularly
interested in creating quality focused, high reliability software.
Some Haskellers started their programming career with Haskell and
stuck to it, but this is still rare. Most Haskellers chose Haskell
after a long journey in search for better tools and improved
productivity. They are often versed in many programming languages
and have explored myriad techniques.
Haskell programmers tend to be well trained and enjoy
understanding the problem domain before starting to code. This
discipline is crucial when working on high-risk projects like
The design and implementation of new programming language
features often happens in Haskell before they are adapted into
other languages. This entices software developers that wish to work
outside of current boundaries. The diversity, passion, and
experience makes the Haskell community a great place to build teams
for creating new technology.
Owning the toolchain
While Haskell and the surrounding tools and libraries are
sophisticated and require effort to get into, those that do master
them find themselves equipped with an unexpected power: being able
to own their entire programming toolchain. An expert Haskell
programmer can modify the code their team writes, the libraries
that the project depends on, down to the Haskell compiler that
creates the final machine code. This “hackability” of the Haskell
toolchain brings various benefits:
- If something doesn't work the way you want or need it too, you
can change it.
- If you need a new compiler feature to make your code safer or
easier to write, you can add it without too much effort.
- If the maintainer of a library you depend on no longer takes
care of it, you can take over maintenance with relative ease. Tools
stack make this straightforward, allowing
you to easily swap out upstream projects with your own forks. This
reduces the risk relying on dependencies exposes to your
- Vetting the code of all your dependencies (which is critical
for safety especially of cryptocurrencies) is a feasible task.
This is different compared to many other programming languages.
Even an expert C++ programmer often does not feel equipped to make
changes to the C++ compiler due to the complexities and sheer
amount of code involved. The GCC compiler has over 7 million lines
The Haskell toolchain is clean and consists of relatively small
amounts of code. GHC totals around 0.5 million lines,
including all of its Haskell dependencies. This makes it possible
for a single programmer to be familiar with Haskell's compiler,
runtime, and libraries in their entirety.
A number of technical and non-technical points come together in
making Haskell a great choice for cryptocurrency implementations.
This is especially true when it comes to safety and programming
One of the biggest strengths of Haskell for cryptocurrencies is
Haskell has a reputation for excelling in these areas.
It is already known and respected for providing strong guarantees
and for being made and used by experts. At time of writing coinmarketcap.com listed 1595 existing
cryptocurrencies. A new cryptocurrency can set itself apart from
that competition by drawing attention to the improved safety and
quality derived from being built in Haskell.
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