What is the difference between a closure and a nested closure?

Question

What is the difference between a closure and a nested closure? A good explanation with examples would be helpful.

Answer 1

Scope of the variables and what environment they are bound to.

And how hard they are to implement in a compiler :)

ClosureA may be bound to it's local scope LA and parent-scope PA, then a closure inside that called ClosureB is bound to (potentially) LB, LA, PA

func a( v1,v2,v3 ){
    closure_b(bv1, bv2, bv3) { # Closure
        b_local1 = bv1
        b_local2 = v1  # parent scope

        closure_c(cv1, cv2) { # Nested closure has 'closure_b's scope too
            c_local1 = cv1
            c_local2 = bv1 # direct-parent scope
            c_local3 = v1 # parent's parent scope (nesting)
            c_local4 = b_local2
        }
        return closure_c;

    }
    return closure_b(); # closure_b() returns closure_c 
}