The object returned by delay in Scheme is "a promise", but promises are not considered to be a type (so there is no promise? procedure, and it's not listed as a type in R5RS or R6RS).
Is there a strong reson why this is so? It would seem quite natural to me to do something like (if (promise? x) (force x) x), for example. (And I see that some implementations will let me force non-promises, and others will not). Also, if I can store something in a variale and pass it around, I feel like it should have a type.
There can't be that strong a reason, since MIT/GNU scheme, defines a promise? function.