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POAccumulating while in recursion/backtracking
 

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    <p>I run into this beginners problem, and i don't know how to solve this. Here is my code:</p> <pre><code>worker( w1, d1, 2000 ) . worker( w2, d1, 2500 ) . worker( w2, d2, 1000 ) . worker( w3, d2, 2000 ) . worker( w4, d2, 4000 ) . % worker( W, D, S ) means that worker W works in department D and has salary S department( d1, w2 ) . department( d2, w4 ) . % department( D, B ) means that worker B is director of department D(this is not important in this case) </code></pre> <p>I need to get sum of all salaries form one of department, like this:</p> <pre><code>?- department_costs( d1 , T ) . T = 4500; no ?- department_costs( D, T ) . D = d1 T = 4500; D = d2 T = 7000; no ?- department_costs( d3 , T ) . no </code></pre> <p>I tried this:</p> <pre><code>department_costs( D, T ):- worker( _X, D, T1 ), T is T1. </code></pre> <p>And I get this:</p> <pre><code>?- department_costs( o1, T ). T=2000; T=2500; no </code></pre> <p>now I need to sum T+T for total costs, but I don't know how to do that. I would like to solve this <strong>without</strong> using findall/setof/bagof.</p> <p><strong>EDIT:</strong></p> <p>I tried with findall:</p> <pre><code>sumL([], 0). sumL([G|R], S):- sumL(R, S1), S is S1 + G. department_costs( D, T ):- findall(P, worker( _X, D, P ), R ), sumL(R, S), T=S. </code></pre> <p>It works fine with department_costs( d1, T ), and department_costs( d2, T ), but when I enter department_costs( D, T ). i get this:</p> <pre><code> department_costs( D, T ). O=_h159 T=11500 </code></pre> <p>and it should be like this:</p> <pre><code> ?- department_costs( D, T ) . D = d1 T = 4500; D = d2 T = 7000; </code></pre> <p>can someone tell what is the problem now?</p>
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