Re: Why does this not work ?

Works for me, and I pasted it directly from your message (see below).

Did you perhaps put

   inventaris(X,Y),item(X,pan,0).

together with the facts in the file?

If you don’t do the query interactively, you’d better make it a query:

  ?- inventaris(X,Y),item(X,pan,0).

but that will only give you a yes (plus a warning about Y).

So it’s better to do

  ?- inventaris(X,Y), item(X,pan,0), write( X ).

or
  :- inventaris(X,Y), item(X,pan,0), write( X ).

if you don’t want the „yes”

or

  :- inventaris(X,_), item(X,pan,0), write( X ).

if you don’t want the warning.

Hope this helps.

— Feliks


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For help, use ?- help(Topic). or ?- apropos(Word).

?- consult(user).
customer(wobben, musselkanaal, aaa).
|: 
|: customer(ankone, hengelo, bbb).
|: 
|: customer("de jong", haaksbergen, ccc). 
|: 
|: 
|: item(1, pan, 0). 
|: 
|: item(2, beker, 1). 
|: 
|: 
|: inventaris( 1, 12). 
|: 
|: inventaris( 2, 10).
|: % user://1 compiled 0.00 sec, 8 clauses
true.

?- inventaris(X,Y),item(X,pan,0).
X = 1,
Y = 12 .

?- 

On Mar 7, 2014, at 20:05, Roelof Wobben <[email protected]> wrote:

> Hello, 
> 
> 
> I have this problem.
> 
> 
> Write a query against the item and inventory records that returns the inventory level for an item when you only know the item name. 
> 
> 
> I have this facts:
> 
> 
> customer(wobben, musselkanaal, aaa).
> 
> customer(ankone, hengelo, bbb).
> 
> customer("de jong", haaksbergen, ccc). 
> 
> 
> item(1, pan, 0). 
> 
> item(2, beker, 1). 
> 
> 
> inventaris( 1, 12). 
> 
> inventaris( 2, 10).
> 
> 
> 
> So I tried this:
> 
> 
> inventaris(X,Y),item(X,pan,0).
> 
> 
> But it gives me a no where I expected it to be 12. 
> 
> 
> Roelof 		 	   		  
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