Here you can find a slightly enhanced version of a simple Prolog interpreter written in C++, by Alan Mycroft.
Original source: https://www.cl.cam.ac.uk/~am21/research/funnel/prolog.c
How to build and run:
mkdir build
cd build
cmake ..
make
./prolog
Expected output:
=== Normal clause order:
solve@0: app(_5,_6,cons(1,cons(2,cons(3,nil))))
try:app(nil,_7,_7) :- true
I = nil
J = cons(1,cons(2,cons(3,nil)))
try:app(cons(_8,_9),_10,cons(_8,_11)) :- app(_9,_10,_11)
solve@1: app(_9,_6,cons(2,cons(3,nil)))
try:app(nil,_12,_12) :- true
I = cons(1,nil)
J = cons(2,cons(3,nil))
try:app(cons(_13,_14),_15,cons(_13,_16)) :- app(_14,_15,_16)
solve@2: app(_14,_6,cons(3,nil))
try:app(nil,_17,_17) :- true
I = cons(1,cons(2,nil))
J = cons(3,nil)
try:app(cons(_18,_19),_20,cons(_18,_21)) :- app(_19,_20,_21)
solve@3: app(_19,_6,nil)
try:app(nil,_22,_22) :- true
I = cons(1,cons(2,cons(3,nil)))
J = nil
try:app(cons(_23,_24),_25,cons(_23,_26)) :- app(_24,_25,_26)
nomatch.
=== Reversed clause order:
solve@0: app(_5,_6,cons(1,cons(2,cons(3,nil))))
try:app(cons(_27,_28),_29,cons(_27,_30)) :- app(_28,_29,_30)
solve@1: app(_28,_6,cons(2,cons(3,nil)))
try:app(cons(_31,_32),_33,cons(_31,_34)) :- app(_32,_33,_34)
solve@2: app(_32,_6,cons(3,nil))
try:app(cons(_35,_36),_37,cons(_35,_38)) :- app(_36,_37,_38)
solve@3: app(_36,_6,nil)
try:app(cons(_39,_40),_41,cons(_39,_42)) :- app(_40,_41,_42)
nomatch.
try:app(nil,_43,_43) :- true
I = cons(1,cons(2,cons(3,nil)))
J = nil
try:app(nil,_44,_44) :- true
I = cons(1,cons(2,nil))
J = cons(3,nil)
try:app(nil,_45,_45) :- true
I = cons(1,nil)
J = cons(2,cons(3,nil))
try:app(nil,_46,_46) :- true
I = nil
J = cons(1,cons(2,cons(3,nil)))