Nesting multiple If-then-else statements - clips

Question

I'm trying to make a CLIPS program that takes in a patient's and donor's blood type and returns if the doctor should go forward with the transfusion. When I load in the program, I get a FALSE flag at the very end. Is there another way that I can nest in the If-Then statements?
; define template
(deftemplate blood-type
(slot blood))
(deftemplate patients
(slot receiver)
(slot donor))
; reading input
(defrule reading-input
=>
(printout t "Enter the receiver/patient blood type: ")
(assert (receiver (read)))
(printout t "Enter the donor's blood type: ")
(assert (donor (read))))
; checking for valid input
(defrule checking-input
(receiver ?receiver)
(donor ?donor)
=>
(if (and (eq ?receiver O) (eq ?donor O))
then
if (and (eq ?receiver A) (eq ?donor A))
then
(if (and (eq ?receiver A)(eq ?donor O))
then
(if (and (eq ?receiver B) (eq ?donor B))
then
(if (and (eq ?receiver B) (eq ?donor O))
then
(if (and (eq ?receiver AB) (eq ?donor AB))
then
(if (and (eq ?receiver AB) (eq ?donor A))
then
(if (and (eq ?receiver AB) (eq ?donor B))
then
(if (and (eq ?receiver AB) (eq ?donor O))
then (printout t "Continue with Transfusion" crlf)
else (printout t "Stop transfusion" crlf))))))))))

Answer 1

Your nesting of conditions is unnecessarily complex. You can achieve the correct results without any nesting:
CLIPS (6.4 2/9/21)
CLIPS>
(defrule read-and-check-input
=>
(printout t "Enter the receiver/patient blood type: ")
(bind ?receiver (read))
(printout t "Enter the donor's blood type: ")
(bind ?donor (read))
(if (or (and (eq ?receiver O) (eq ?donor O))
(and (eq ?receiver A) (eq ?donor A))
(and (eq ?receiver A)(eq ?donor O))
(and (eq ?receiver B) (eq ?donor B))
(and (eq ?receiver B) (eq ?donor O))
(and (eq ?receiver AB) (eq ?donor AB))
(and (eq ?receiver AB) (eq ?donor A))
(and (eq ?receiver AB) (eq ?donor B))
(and (eq ?receiver AB) (eq ?donor O)))
then (printout t "Continue with Transfusion" crlf)
else (printout t "Stop transfusion" crlf)))
CLIPS> (reset)
CLIPS> (run)
Enter the receiver/patient blood type: A
Enter the donor's blood type: O
Continue with Transfusion
CLIPS> (reset)
CLIPS> (run)
Enter the receiver/patient blood type: B
Enter the donor's blood type: AB
Stop transfusion
CLIPS>
If this is for a class assignment, you might get a failing grade using an approach that doesn't utilize pattern matching in a meaningful way.