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POOutput only the sad students from a list in Prolog
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  1. POOutput only the sad students from a list in Prolog
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    copied!<p>I have the following declaration:</p> <pre><code>calculate_sad_moods([]):-!. calculate_sad_moods([X2|Rest2]) :- (sad(X2),write(`One of our sad students is: `),write(X2),nl); calculate_sad_moods(Rest2). </code></pre> <p>When I call it like this:</p> <pre><code>?- calculate_sad_moods([ ivan, dragan, petkan, borislav, damyan, ani, petyr, ivo ]). </code></pre> <p>I end up with a very long list like this (It's ok, but it has dublicate records):</p> <pre><code>One of our sad students is: ivan Yes. One of our sad students is: dragan Yes. One of our sad students is: dragan Yes. One of our sad students is: petkan Yes. One of our sad students is: petkan Yes. One of our sad students is: borislav Yes. One of our sad students is: borislav Yes. One of our sad students is: damyan Yes. One of our sad students is: damyan Yes. One of our sad students is: damyan Yes. One of our sad students is: ani Yes. One of our sad students is: ani Yes. One of our sad students is: ani Yes. One of our sad students is: petyr Yes. One of our sad students is: petyr </code></pre> <p>When I change the declaration to:</p> <pre><code>calculate_sad_moods([]):-!. calculate_sad_moods([X2|Rest2]) :- write(`One of our sad students is: `),write(X2),nl, calculate_sad_moods(Rest2). </code></pre> <p>I end up with this (It's not OK, because not everybody is sad, but it has no dublicate records):</p> <pre><code>One of our sad students is: ivan One of our sad students is: dragan One of our sad students is: petkan One of our sad students is: borislav One of our sad students is: damyan One of our sad students is: ani One of our sad students is: petyr One of our sad students is: ivo </code></pre> <p>How can I output only the sad students and only once? I've tried adding brackets and several other tricks and still - Nothing. I have no other ideas left where to look.</p> <p><strong>P.S: Here's how the sad declaration looks like</strong></p> <pre><code>[...] sad(damyan) :- (not(lovesExam(damyan,chemistry)),hasExam(damyan,chemistry)); (not(lovesExam(damyan,biology),hasExam(damyan,biology))); (not(lovesExam(damyan,math),hasExam(damyan,math))). sad(ani) :- (not(lovesExam(ani,chemistry)),hasExam(ani,chemistry)); (not(lovesExam(ani,biology),hasExam(ani,biology))); (not(lovesExam(ani,math),hasExam(ani,math))). [...] </code></pre> <p>It'is still very obscure, but I'm still learning the basics...</p>
 

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