Contracts enable specifying conditions that must hold true when the flow of runtime execution reaches the contract. If a contract is not true, then the program is assumed to have entered an undefined state.

Rationale: Building contract support into the language provides:

1. a consistent look and feel for the contracts
2. tool support
3. the implementation can generate better code using information gathered from the contracts
4. easier management and enforcement of contracts
5. handling of contract inheritance

1. Assert Contract
2. Pre and Post Contracts
3. Invariants
4. References