Erlang vs Reason ML

Erlang has strong roots with the telecom industry in which concurrent processes are normal. It's designed to be concurrent, to be used for distributed computing and to be scalable.

Fault tolerance means that a system has the property to continue operating even though one or more components have failed.

For Erlang systems, this means that the system is kept running even if for example a user has to drop a phone call rather than forcing everyone else to do so.

In order to achieve this, Erlang's VM gives you:

• Knowledge of when a process died and why that happened
• The ability to force processes to die together if they depend on each other and if one of them has a fault.
• A logger that logs every uncaught exception
• Nodes that can be monitored so that you find out when they go down
• The ability to restart failed processes (or groups of them)

In a real-time system it may not be possible to stop the system in order to implement code upgrades. For these cases Erlang gives you dynamic code upgrade support for free when using OTP. The mechanism is very easy to understand and works as follows:

1. Start the app
2. Edit the code
3. Recompile

That's all that is needed, the app updates with the new code while it's still running and tests are run automatically.

Erlang is made to be parallel and distributed. Because it's very easy to write code that uses multiple processor cores, it's also very easy to write applications that span multiple servers.

Erlang has been used in production for more than 20 years now. During that time it has proven itself over and over again that works great in both small startups and large-scale enterprise systems.

Erlang has been used extensively by Ericsson themselves. For example, the AXD301 ATM, which is one of Ericsson's flagships is probably the largest Erlang project ever with more than 1.1 million lines of Erlang code.

Erlang's processes have very little overhead (about 500 bytes per process). This means that a huge amount of processes can be created, even on older machines.

Erlang's processes run in a complete independent way from the OS (they aren't managed by the OS scheduler neither). This means that programs written in Erlang will run exactly the same way regardless of the operating system or platform.

Ocaml type inference is so smart that you never have to repeat yourself and keep code very clean, type errors also are very pleasant.

Despite being a completely different language Javascript programmer will find that the syntax of ReasonML has many familiarities with Javascript.

unlike other js-targetting languages that are thought as a way to have a language that pleases community X run in a browser, reason is really designed with JavaScript community in mind. it removes the bad parts but keeps its syntax and its best design principles (from Scheme): simplicity, minimalism, and functions as building block.

reason includes true immutability, but it has escape hatches to let you use mutations in exceptional cases.

The same reasonml code can compile to js (eg. run on browsers or node.js, use any lib in npm), or compile to assembly thru ocaml (unless of course you load js externals), running on any device, with C-comparable (or better) performance.

Reason was created by the creator of react, for developers already using JSX to template web or native UIs this results very familiar.