Here I place a Prolog procedure to encode the runlength of a list of symbols. For example: 
[12,2,2,w,3,3,s,s,s,] maps to [1*12,2*2,1*w,2*3,3*s]

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runcode([],C,N,[N*C]).
runcode([H | T],H,N,Z) :- N1 is N+1,runcode(T,H,N1,Z).
runcode([H | T],C,N,[N*C| Z]) :- H\==C,runcode(T,H,1,Z).

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In reply to PPGA - Prolog-Perl Golf Association: Run-length encoding by princepawn

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