Narcissistic Number in Prolog

hi everyone I'm here again, this week I got this Homework:

I should find all the numbers between 10 and 10000 which has property like the following example:

89 = 8^1 + 9^2
2427 = 2^1 + 4^2 + 2^3 + 7^4 = 2 + 16 + 8 + 2401

I have this in Haskell implemented, and it works just fine(I think) and return a List like this:

[89,135,175,518,598,1306,1676,2427]

and then I tried to write it in Prolog(as required too) like the following:

num(0).
num(1).
num(2).
num(3).
num(4).
num(5).
num(6).
num(7).
num(8).
num(9).

allNarc(X):- num(A),num(B),num(C),num(D),
             X = A*1000+B*100+C*10+D,Y = A**1+B**2+C**3+D**4,
             X =:= Y,X>10.
allNarc(X):- num(B),num(C),num(D),
             X = B*100+C*10+D,Y = B**1+C**2+D**3,
             X =:= Y,X>10.
allNarc(X):- num(C),num(D),
             X = C*10+D,Y = C**1+D**2,
             X =:= Y,X>10.

the result is something like this:

?- allNarc(X).
X = 1*1000+3*100+0*10+6 ;
X = 1*1000+6*100+7*10+6 ;
X = 2*1000+4*100+2*10+7 ;
X = 0*100+4*10+3 ;    <- 43
X = 0*100+6*10+3 ;    <- 63
X = 1*100+3*10+5 ;
X = 1*100+7*10+5 ;
X = 5*100+1*10+8 开发者_运维百科;
X = 5*100+9*10+8 ;
X = 8*10+9 ;
false.

clearly 43 and 64 should not belong to this group and the result is just ugly, can anyone help me to get output like the result in my Haskell implementation?

---

Two points.

1. when you say X = you are unifying the left and right sides of =. If you want X to be a number equal to evaluating the expression, use X is <expression here> .
2. you want to prevent a zero in the first position: num(A), A \= 0, num(B), ...

After making those changes I get:

?- allNarc(X).
X = 1306 ? ;
X = 1676 ? ;
X = 2427 ? ;
X = 135 ? ;
X = 175 ? ;
X = 518 ? ;
X = 598 ? ;
X = 89 ? ;
no

You could also use bagof to collect the values. e.g. bagof(X,allNarc(X),Narcs). Narcs is then a list of your values.

---

You need to:

1. Prevent the first digits being 0.
2. Make sure that X is evaluated to the value you want. At the moment you are using term unification which is not appropriate, you need to use the is keyword.

See:

num(0).
num(1).
num(2).
num(3).
num(4).
num(5).
num(6).
num(7).
num(8).
num(9).
posnum(A) :- num(A), A \= 0.

allNarc(X):- posnum(A),num(B),num(C),num(D),
             X is A*1000+B*100+C*10+D,Y is A**1+B**2+C**3+D**4,
             X =:= Y,X>10.
allNarc(X):- posnum(B),num(C),num(D),
             X is B*100+C*10+D,Y is B**1+C**2+D**3,
             X =:= Y,X>10.
allNarc(X):- posnum(C),num(D),
             X is C*10+D,Y is C**1+D**2,
             X =:= Y,X>10.

Note that you can then find all the numbers using setof:

?- setof(X,allNarc(X),XL).
XL = [89, 135, 175, 518, 598, 1306, 1676, 2427].

This is much more convenient that listing through them one by one.