tests whether the provided forms are promises
(promise? form+) (!promise? form+) (is-promise form)
If all forms evaluate to a promise, then this function will return #t (true). The first non-promise will result in the function returning #f (false).
(define p1 (promise "one")) (define p2 (promise "two")) (promise? p1 p2 [1 2 3])
This example will return #f (false) because the third form is a vector.
Like most predicates, this function can also be negated by prepending the
! character. This means that all of the provided forms must not be promises.
(!promise? "hello" [1 2 3])
This example will return #t (true).