Write a function concat$\_$elements$($slist$,$ startpos, stoppos$),$ where slist is a list of strings and startpos and stoppos are integers, that concatenates the elements of slist starting at position startpos and ending at position stoppos $($inclusive$)$ and returns the resulting string.

Your code should behave reasonably for all values of startpos and stoppos: if startpos is negative, concatenation should start with the first element of slist; if stoppos $>=$ len$($slist$),$ concatenation should stop at the last element of slist. If startpos $>$ stoppos it should return the empty string. See the examples below.