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1 total messages Started by "Shira Rotman" Thu, 11 Apr 2002 23:41

Author: "Shira Rotman"
Date: Thu, 11 Apr 2002 23:41

34 lines
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Hello,

I have this code:

swap([],[]).
swap([X],[X]).
swap([X,Y|L1],[X,Y|L2]):-X=<Y,swap([Y|L1],[Y|L2]).
swap([X,Y|L1],[Y,X|L2]):-X>Y,swap([X|L1],[X|L2]).

When I try to run it by typing: "?-swap([2,5,4,7,6],X).", it first gets to
line 3 and calls swap([5,4,7,6],[5|_G367]). Then it checks if 5=<4 and
fails, but it doesn't continue to line 4 to check if 5>4, but returns to the
original call (with [2,5,4,7,6]) and then continues to line 4, checks if
2>5, fails and prints "No".

I don't understand why it doesn't continue to line 4 to check if 5>4 after
it fails in line 3 in the second call. Does somebody have a solution?

Thanks.



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