number-of-results

(in-package "ACL2")

(define number-of-results
  ((fn symbolp) (wrld plist-worldp))
  :guard (not (member-eq fn *stobjs-out-invalid*))
  :returns (n natp "Actually always a @(tsee posp).")
  :parents (std/system/function-queries)
  :short "Number of values returned by a named function."
  :long (topstring (p "This is 1, unless the function uses @(tsee mv)
     (directly, or indirectly by calling another function that does)
     to return multiple values.")
    (p "The number of results of the function
     is the length of its @(tsee stobjs-out) list.")
    (p "The function must not be in @('*stobjs-out-invalid*'),
     because in that case the number of its results
     depends on how it is called.")
    (p "See @(tsee number-of-results+) for
     an enhanced variant of this utility."))
  (len (stobjs-out fn wrld)))