sealed class Ctx
class SimpleCtx : Ctx()
class ComplexCtx : Ctx()

typealias SimpleCtxF<T> = (SimpleCtx) -> T
typealias ComplexCtxF<T> = (ComplexCtx) -> T

fun <T> evalSimple(simpleCtxF: SimpleCtxF<T>): T = evalImpl(SimpleCtx(), simpleCtxF)

fun <T> evalComplex(complexCtxF: ComplexCtxF<T>): T = evalImpl(ComplexCtx(), complexCtxF)

private fun <CTX : Ctx, T> evalImpl(ctx: CTX, f: (CTX) -> T): T {
    /** some common actions */
    val isComplex = when (ctx as Ctx) {
        is SimpleCtx -> false
        is ComplexCtx -> true
    }
    return try {
        if (isComplex) {
            /** pre eval actions for complex context */
        }
        val t = f(ctx)
        if (isComplex) {
            /** on success actions for complex context */
        }
        t
    } catch (t: Throwable) {
        if (isComplex) {
            /** on failure actions for complex context */
        }
        throw t
    } finally {
        if (isComplex) {
            /** cleanup actions for complex context */
        }
    }
}