<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"> Hi Raphael, I am almost there. It compiles well but am not getting the correct results. The results i get now is only one tuple in the list: [{3, 1}] Here is the problem. I have made changes to the following functions: I don't understand what u mean by updating Freqs with recursion. i think concatenating [{J,N}] to it is the update since OR?. Since it handle one list item at a time as you explained in your previous mail, why do i need to do recursion here? Can u give me some a little explanation. i think it may be the problem. :- func inc_freq(T, list({T,int})) = list({T,int}). inc_freq(I, []) = [{I,1}]. inc_freq(I, [{J,N}|Freqs]) = (if (I = J) then [{J,N+1}|Freqs] % I's counter incremented, rest untouched else Freqs ++ [{J,N}] % keep J in the list, but increment the ). % frequency of I in Freqs I have just put inc_freq(X,FreqList) as the second argument to the last statement. is is correct?: :- func tabel_aux(list(T), list({T,int})) = list({T,int}). tabel_aux([], FreqList) = FreqList. tabel_aux([X|Xs], FreqList) = % inc_freq(X,FreqList) ++ tabel_aux(Xs,inc_freq(X,FreqList)). Thanks for your help. I appreciate it so much. Regards, Eddie. --- On Fri, 12/17/10, Raphael Collet <rco@missioncriticalit.com> wrote: <blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"> From: Raphael Collet <rco@missioncriticalit.com> Subject: Re: Yet Another Bug: Converting List To List Of Tuples To: "win1for@yahoo.com" <win1for@yahoo.com> Cc: mercury-users@csse.unimelb.edu.au Date: Friday, December 17, 2010, 11:15 AM <div class="plainMail">On 12/17/2010 05:02 PM, <a ymailto="mailto:win1for@yahoo.com" href="/mc/compose?to=win1for@yahoo.com">win1for@yahoo.com</a> wrote: > Hi Raphael, > > I have made the necessary changes and the code look like this. Now i > have a new error: > > this is the code: > > ************************************************************************************ > :- module oplossing1. > > :- interface. > :- import_module io. > > :- pred main(io.state::di, io.state::uo) is det. > > :- implementation. > :- import_module int, list,string,map. > > :- func tabel(list(T)) = list({T,int}). The compilation error is here: > tabel([]) = []. > tabel([X]) = tabel_aux([X], []). You handle only lists with zero or one element. You don't handle *any* list. Actually tabel_aux works for any list, so you don't need to do pattern matching in tabel... > > > :- func inc_freq(T, list({T,int})) = list({T,int}). > inc_freq(I, []) = [{I,1}]. > inc_freq(I, [{J,N}|Freqs]) = (if (I = J) > then [{J,N+1}|Freqs] % I's counter incremented, rest untouched > else Freqs ++ [{J,N}] % keep J in the list, but increment the > ). % frequency of I in Freqs Wait, there is a mistake here above. You don't update Freqs. Maybe some recursion is needed... > > > :- func tabel_aux(list(T), list({T,int})) = list({T,int}). > tabel_aux([], FreqList) = FreqList. > tabel_aux([X|Xs], FreqList) = inc_freq(X,FreqList) ++ > tabel_aux(Xs,FreqList). I don't understand. Why are you concatenating frequency lists? inc_freq(X,FreqList) is the updated frequency list after processing X. You should use that one for processing the next element... > > > :- func compare_freq({T,int}, {T,int}) = comparison_result. > compare_freq({_, N1}, {_, N2}) = Result :- > compare(Result, N1, N2). > > main(!IO):- > %io.print(tabel(string.to_char_list("this is a test")),!IO), > io.nl(!IO), > io.print(tabel([3,2,1,2,1,1,2]),!IO), > io.nl(!IO). > </div></blockquote></td></tr></table>