Fix: Saves result of forcing promise back into environment, instead of re-evaluating it every time.
Chore: Renames Closure to Promise. Maybe eventually there will be a need for both, but for now I think Promise is a better indication of what this represents. A Closure might be better represented by a function anyways (I think internally R refers to its functions as "closures" anyways since they always capture their environments).
Closes #122
Fix: Saves result of forcing promise back into environment, instead of re-evaluating it every time.
Chore: Renames
ClosuretoPromise. Maybe eventually there will be a need for both, but for now I thinkPromiseis a better indication of what this represents. AClosuremight be better represented by a function anyways (I think internally R refers to its functions as "closures" anyways since they always capture their environments).