我正在编写一个猜测动物的专家系统。这是讲师提供的一个例子。我使用视觉序言，但我收到了编译错误，我无法理解。你能帮帮我吗？
#include @"pfc\core.ph"
implement program
open core
class facts -database
db_make_sure : (symbol,symbol).
db_denied : (symbol,symbol).
have_found : (symbol).
predicates
do_animal : ().
find_animal : ().
it_is : (symbol).
make_sure : (symbol,symbol).
denied : (symbol,symbol).
remember : (symbol,symbol,symbol).
ask : (symbol,symbol).
test1 : (symbol).
test2 : (symbol,symbol).
test3 : (symbol,symbol,symbol).
test4 : (symbol,symbol,symbol,symbol).
do_expert_job : ().
clear_facts : ().
/* USER INTERFACE SYSTEM */
clauses
do_expert_job() :-
console::nl,console::write("---------------------------------------"),
console::nl,console::write("| WELCOME TO A ANIMAL EXPERT SYSTEM |"),
console::nl,console::write("| |"),
console::nl,console::write("| This is a classification program |"),
console::nl,console::write("| (it guesses animals) |"),
console::nl,console::write("| that works by forwards chaining. |"),
console::nl,console::write("| Please respond by typing in |"),
console::nl,console::write("| 'yes' or 'no' |"),
console::nl,console::write("---------------------------------------"),
console::nl,console::nl,
do_animal,
console::write(" Press Space Bar "),console::nl,
_ = console::readChar(),
console::clearOutput,
console::close.
do_animal():-
find_animal,
have_found(X),!,console::nl,
console::write(" Your animal may be a(n) ",X,"."), console::nl,
_ = console::readChar(),
clear_facts.
do_animal() :-
console::nl,console::write(" Sorry , unable to determine the animal."), console::nl,
_ = console::readChar(),
clear_facts.
ask(X,Y) :-
console::write("Question :- ",X," it , ",Y," ? "),
R = console::readLine(),
remember(X,Y,R).
/* INFERENCE ENGINE */
find_animal() :-
test1(X),
test2(X,Y),
test3(X,Y,Z),
test4(X,Y,Z,_),!.
find_animal().
make_sure(X,Y) :- db_make_sure(X,Y),!.
make_sure(X,Y) :- not(denied(X,Y)),!, ask(X,Y).
denied(X,Y) :- db_denied(X,Y),!.
remember(X,Y,'yes'):- asserta(db_make_sure(X,Y)).
remember(X,Y,'no'):- asserta(db_denied(X,Y)), fail.
clear_facts() :- retract(db_make_sure(_,_)), fail.
clear_facts() :- retract(db_denied(_,_)), fail.
/* PRODUCTION RULES */
test1(_M) :- it_is('mammal'),!.
test1(_N).
test2(_M,_C) :- it_is('carnivorous'),!.
test2(_M,_N).
test2(_N,_W) :- make_sure('does','swim'),!.
test2(N,N).
test3(_M, _C, _S) :- make_sure('has','stripes'), asserta(have_found('tiger')),!.
test3(_M, _C, _N) :- asserta(have_found('cheetah')).
test3(_M, _N, _L) :- not(make_sure('does','swim')), not(make_sure('does','fly')),!.
test3(_M, N, N) :- asserta(have_found('blue whale')).
test3(N, N, _F) :- make_sure('does','fly'), asserta(have_found('eagle')),!.
test3(N, N, N) :- asserta(have_found('ostrich')).
test3(_N, _W, _T) :- make_sure('has','tentacles'), asserta(have_found('octopus')),!.
test3(N, _W, N).
test4(_M, _N, _L, _S) :- make_sure('has','stripes'), asserta(have_found('zebra')),!.
test4(_M, N, _L, N) :- asserta(have_found('giraffe')).
test4(N, _W, N, _F) :- make_sure('has','feathers'), asserta(have_found('penguin')),!.
test4(N, _W, N, N) :- asserta(have_found('sardine')).
it_is('mammal') :- make_sure('has','hair'),!.
it_is('mammal') :- make_sure('does','give_milk'),!.
it_is('carnivorous') :- make_sure('has','pointed_teeth'),!.
it_is('carnivorous') :- make_sure('does','eat_meat'),!.
it_is('ungulate') :- it_is('mammal'),
make_sure('has','hooves'), make_sure('does','chew_cud'),!.
it_is('bird') :- not(it_is('mammal')),
make_sure('has','feathers'), make_sure('does','lay_eggs'),!.
it_is('fish') :- make_sure('does','swim'), make_sure('has','fins'),!.
end implement program
我收到了以下错误：
The expression has type '::string', which is incompatible with the type '::symbol'
The flow pattern '(o)' does not exist for 'program::test1/1'
The flow pattern '(o)' does not exist for 'program::test1/1'
首先出错：
remember(X,Y,R)