Bengt Kleberg <>
Tue Feb 10 09:06:53 CET 2015

```You are correct it is nopt possibler to have sum/1 followed by sum/2
with an ";" between them. They are different functions that happen to
have the same name. But since the arity (number of arguments) is
different they are different.

bengt

On 02/10/2015 09:01 AM, Roelof Wobben wrote:
> Hello,
>
> I changed my code so that it also can count from a number to a number,
> so sum(3,6) does 3+4+5+6 and sum(2) does 0+1+2
>
> I now have this :
>
> -module(sum_recursion).
>
> -export([sum/1, sum/2]).
>
> % when the number is zero the outcome will also be zero
> sum(0) ->
>   0;
>
> % when a number is greater then 0 , call the helper function.
> sum(End) when End > 0 ->
>   sum_acc(End,0);
>
> % when the first number is greater then zero and lower then the second
> number
> sum(Begin, End) when Begin >= 0 , Begin =< End ->
>   sum_acc(Begin, End, Begin).
>
> % When End is equal to zero all the numbers are added
> sum_acc(0,Acc) ->
>      Acc;
>
> % When End is equal to Begin all numbers are added.
> sum_acc(Begin, Begin, Acc) ->
>   Acc ;
>
> % when end is not zero there are more numbers to be added.
> sum_acc(End, Acc) ->
>      sum_acc(End - 1, Acc + End);
>
> % When end is not equal to begin then there are more numbers to be added.
> sum_acc(Begin, End, Acc) ->
>   sum_acc(Begin, End - 1, Acc + End).
>
>
> but as soon as I try to compile it I see this error :
>
> error
> 7> c(sum_recursion).
> sum_recursion.erl:3: function sum/1 undefined
> sum_recursion.erl:3: function sum/2 undefined
>
> Am I not alllowed to do this
>
> sum(x) ->
>    x ;
>
> sum(x,y) ->
>   x + y.
>
> or is there something else missing ?
>
> Roelof
>
>
>
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