* Improve front-end language

- Tuple syntax in expressions, types and patterns? Implemented with records.

- List syntax in types and patterns? Implemented with List.

- implicit arguments?

- show generation

- eq generation

- better module system

- Negated patterns?

- Patterns with guards

* Improve interpreter

- More efficient handling of constructor application

- Implement tail recursion.

* Improve the core language

* Improve compilation

* Add primitive operations to core

- primitive operations on strings:

- add floating-point numbers with primitive oeprations?

* Implement module system in interpreter

* Add type checker for core

* Add friendly type checker for front-end language

* Add termination checker
