Enum Mode 

pub enum Mode {
    Eval {
        env: Env,
        exp: RcExp,
    },
    Apply {
        val: Val,
    },
}

The CK machine alternates between two modes:

• Eval: we have an Exp to evaluate under Env. The dispatcher step_eval inspects the Exp and either produces a Val immediately (literals, vars, lambdas) or pushes a Cont and switches to evaluating a sub-expression.

• Apply: we have a finished Val. The dispatcher pops the topmost Cont from the kont stack and integrates the Val into whatever pending operation that continuation represents — possibly producing another Eval step (for the next operand), another Apply step (the operation produced a final value), or terminating the loop (kont stack empty).

Variants

Eval

Evaluate exp under env. The result is fed to whatever continuation is on top of the stack.

Fields

env: Env

Environment to evaluate under.

exp: RcExp

Expression to evaluate.

Apply

Apply the topmost continuation to val. If the stack is empty, val is the final result.

Fields

val: Val

The value just produced.