Clarity reference - Part 1 / Primitivess

Clarity differs from most other smart contract languages in two important ways:

• It is decidable which means programs must necessarily terminate
• It is interpreted and broadcasted on the network as-is

Contracts composition

• Data — the space which only the smart contract itself may modify
• Functions — operate within the data space of the smart contract

Language features

• No recursion
• No lambdas
• No mutation
• Loops only via fold, map and filter
• Atomic semantics on booleans, integers, principals, buffers
• Functions, pure (read-only) and impure (modify state)

Functions / pure

• Specified via define-read-only
• Return any type
• No state mutations — result in an error otherwise

Functions / impure

• Specified via define-public
• Return a Response type result where
  • ok means the function is considered valid
  • err means the function is considered invalid

Let’s assume that function A calls function B

• A returns err, B returns ok
  • no effects from A
  • no effects from B
• A returns ok, B returns err
  • effects from A
  • no effects from B
• A returns ok, B returns ok
  • effects from A
  • effects from B

Support for lists

• Multi-dimensional, of the same type
• fold, map and filter on lists
• Variable length when used as function inputs
  • An extra constant parameter required that indicates the maximum output size when used as function outputs

Next: Clarity reference — Part 2 / Data-Space Primitives.