Nickel is the universal configuration language. Nickel is
configuration templating, but done right. Modular, correct
and concise.

Its purpose is to automate the generation of static
configuration files - think JSON, YAML, XML, or your
favorite data representation language - that are then fed
to another system.

Nickel's salient traits are:

* Composable code: functions are first-class citizens.
* Composable data: records can be composed through the
  merge operator.
* Typed, but only when it helps: a gradual type system.
* Design by contract: contracts act like schemas.