Made me think of Racket's custodians: http://docs.racket-lang.org/reference/eval-model.html#%28part._custodian-model%29 http://docs.racket-lang.org/reference/e

Made me think of Racket's custodians: http://docs.racket-lang.org/reference/eval-model.html#%28part._custodian-model%29 http://docs.racket-lang.org/reference/eval-model.html#%28par...