Named Values

A “named value” is what you might call a “variable” in other languages. The distinction is important, though. Aranya Policy Language is a static single assignment language. In a particular scope, a named value is defined once and never mutated. Some values may be predefined in some scopes, or inherited from enclosing scopes.

let x = 3
let x = 4  // Error - cannot redefine `x`
if foo is None {
    let x = 5  // Can't shadow in an inner scope, either.
    let y = x + 1  // `x` is inherited from the enclosing scope
}

Automatically defined named values

In some contexts, there are names automatically defined by the runtime.

• In policy, recall, and seal blocks, the fields of the command are available via the name this, which is of type struct <CommandName>.
• In policy, recall, and open blocks, the envelope of the command is available via the name envelope, which is an opaque type accessible via the envelope FFI.