Scheme Exercises

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Group:     Exercise: 29/48 

positionOf:  Find the position of the first occurrence of an element inside a list

(Difficult): Create the function "positionOf" which will be given an element and a list and will return the position of the first occurrence of the element inside the list. It will return 0 if the element is not found. For instance:
(positionOf 'a '(a b c)) ; -> 1
(positionOf 'b '(a b c b)) ; -> 2 (remember: first occurrence)
(positionOf 'c '(a b d)) ; -> 0