Problem with depth first search output in prolog
up vote
1
down vote
favorite
I have the following code:
s(a, b).
s(b, c).
goal(c).
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).
When I enter the query:
solve(a, P).
It gives me :
P = [_,_,c] ?
yes
But I want the complete path e.g.
P = [a,b,c] ?
prolog
edited Nov 9 at 11:47
false
10.9k769141
asked Nov 9 at 9:30
sosscs
706
add a comment |
up vote
1
down vote
favorite
I have the following code:
s(a, b).
s(b, c).
goal(c).
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).
When I enter the query:
solve(a, P).
It gives me :
P = [_,_,c] ?
yes
But I want the complete path e.g.
P = [a,b,c] ?
prolog
edited Nov 9 at 11:47
false
10.9k769141
asked Nov 9 at 9:30
sosscs
706
You mixed upNlandN1.
– Willem Van Onsem
Nov 9 at 9:32
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I have the following code:
s(a, b).
s(b, c).
goal(c).
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).
When I enter the query:
solve(a, P).
It gives me :
P = [_,_,c] ?
yes
But I want the complete path e.g.
P = [a,b,c] ?
prolog
edited Nov 9 at 11:47
false
10.9k769141
asked Nov 9 at 9:30
sosscs
706
I have the following code:
s(a, b).
s(b, c).
goal(c).
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).
When I enter the query:
solve(a, P).
It gives me :
P = [_,_,c] ?
yes
But I want the complete path e.g.
P = [a,b,c] ?
prolog
prolog
edited Nov 9 at 11:47
false
10.9k769141
asked Nov 9 at 9:30
sosscs
706
edited Nov 9 at 11:47
false
10.9k769141
asked Nov 9 at 9:30
sosscs
706
edited Nov 9 at 11:47
false
10.9k769141
edited Nov 9 at 11:47
false
10.9k769141
edited Nov 9 at 11:47
false
10.9k769141
10.9k769141
asked Nov 9 at 9:30
sosscs
706
asked Nov 9 at 9:30
sosscs
706
asked Nov 9 at 9:30
sosscs
706
706
You mixed upNlandN1.
– Willem Van Onsem
Nov 9 at 9:32
add a comment |
You mixed upNlandN1.
– Willem Van Onsem
Nov 9 at 9:32
You mixed up
Nl and N1.– Willem Van Onsem
Nov 9 at 9:32
You mixed up
Nl and N1.– Willem Van Onsem
Nov 9 at 9:32
add a comment |
1 Answer
1
active
oldest
votes
up vote
1
down vote
accepted
In your predicate you use two variables that look similar (graphically):
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).Here Nl (with a lowercase L) looks similar to N1 (with a one 1). In fact the Prolog interpreter recognizes that N1 is only used once, and raises a warning:
?- ['file.pl'].
Warning: /tmp/file.pl:8:
Singleton variables: [N1]
true.The N1 variable has nothing to do with the Nl variable defined in the body, and thus remains ununified.
But that being said, if you really want to output here, you should use N in the "path" construction, not N1, since otherwise for solve(a, L), L will start with b, not a, and will mention the last node (here c) twice, so:
solve( N, [N] ) :-
goal( N).
solve(N, [N | Sol]) :-
s(N, Nl),
solve(Nl, Sol).answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
accepted
In your predicate you use two variables that look similar (graphically):
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).Here Nl (with a lowercase L) looks similar to N1 (with a one 1). In fact the Prolog interpreter recognizes that N1 is only used once, and raises a warning:
?- ['file.pl'].
Warning: /tmp/file.pl:8:
Singleton variables: [N1]
true.The N1 variable has nothing to do with the Nl variable defined in the body, and thus remains ununified.
But that being said, if you really want to output here, you should use N in the "path" construction, not N1, since otherwise for solve(a, L), L will start with b, not a, and will mention the last node (here c) twice, so:
solve( N, [N] ) :-
goal( N).
solve(N, [N | Sol]) :-
s(N, Nl),
solve(Nl, Sol).answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
add a comment |
up vote
1
down vote
accepted
In your predicate you use two variables that look similar (graphically):
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).Here Nl (with a lowercase L) looks similar to N1 (with a one 1). In fact the Prolog interpreter recognizes that N1 is only used once, and raises a warning:
?- ['file.pl'].
Warning: /tmp/file.pl:8:
Singleton variables: [N1]
true.The N1 variable has nothing to do with the Nl variable defined in the body, and thus remains ununified.
But that being said, if you really want to output here, you should use N in the "path" construction, not N1, since otherwise for solve(a, L), L will start with b, not a, and will mention the last node (here c) twice, so:
solve( N, [N] ) :-
goal( N).
solve(N, [N | Sol]) :-
s(N, Nl),
solve(Nl, Sol).answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
add a comment |
up vote
1
down vote
accepted
up vote
1
down vote
accepted
In your predicate you use two variables that look similar (graphically):
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).Here Nl (with a lowercase L) looks similar to N1 (with a one 1). In fact the Prolog interpreter recognizes that N1 is only used once, and raises a warning:
?- ['file.pl'].
Warning: /tmp/file.pl:8:
Singleton variables: [N1]
true.The N1 variable has nothing to do with the Nl variable defined in the body, and thus remains ununified.
But that being said, if you really want to output here, you should use N in the "path" construction, not N1, since otherwise for solve(a, L), L will start with b, not a, and will mention the last node (here c) twice, so:
solve( N, [N] ) :-
goal( N).
solve(N, [N | Sol]) :-
s(N, Nl),
solve(Nl, Sol).answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
In your predicate you use two variables that look similar (graphically):
solve( N, [N] ) :-
goal( N).
solve( N, [N1 | Sol] ) :-
s( N, Nl),
solve( Nl, Sol).Here Nl (with a lowercase L) looks similar to N1 (with a one 1). In fact the Prolog interpreter recognizes that N1 is only used once, and raises a warning:
?- ['file.pl'].
Warning: /tmp/file.pl:8:
Singleton variables: [N1]
true.The N1 variable has nothing to do with the Nl variable defined in the body, and thus remains ununified.
But that being said, if you really want to output here, you should use N in the "path" construction, not N1, since otherwise for solve(a, L), L will start with b, not a, and will mention the last node (here c) twice, so:
solve( N, [N] ) :-
goal( N).
solve(N, [N | Sol]) :-
s(N, Nl),
solve(Nl, Sol).answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
answered Nov 9 at 9:36
Willem Van Onsem
140k16132225
140k16132225
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
add a comment |
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
Thanks, that helped. What is your secrete for learning prolog? our instructor isn't teaching us much.
– sosscs
Nov 9 at 10:41
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
@sosscs: I think Learn Prolog Now! can be quite helpful.
– Willem Van Onsem
Nov 9 at 17:02
add a comment |
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You mixed up
NlandN1.– Willem Van Onsem
Nov 9 at 9:32