Expressions

A base expression consists of a primitive type along with an optional role specifier. For instance the expression "Hello"@Alice evaluates to a value of type String@Alice. If no role is specified, then the value of the resulting value will exist at all roles in the current scope. Thus, in the example below, x will have type String@[A,B,C].

func@(A,B,C) main() {
  let x = "hello";
}

Binary operations

The following binary operations are supported:

• + addition, - subtraction, / division, % modulo.
• == equality, != negated equality.
• < less than, <= less than or equal, > greater than, >= greater than or equal.
• && logical and, || logical or

Binary operations are only allowed if the types of the two values have intersecting roles. This means that Int@A + Int@A is not allowed, but Int@A + Int@B is not.

When carrying out operations on shared types, the result will exist at the intersection of the roles.

let x: Int@[A,B,C] = 5;
let y: Int@[B,C,D] = 7;

let sum: Int@[C,D] = x + y;

Other expressions

• Await async value await x
• Struct construction
• Function calling myFunction()
• List construction [1,2,3]
• List indexing list[i]
• Communication A->B value

Closure construction

See closures for more details.

let x = func@(A,B) (input: Int@A) Int@B {
  return await A->B input;
};

Field access

Some types have fields that can be accessed as value.field. This includes:

• Fields of structures
• Methods of interfaces
• The .length field of lists