@scan(f:function, t:tab)


returns the tab of the partial reduction by f of the elements of t:

       [ t[0], f(t[0],t[1]), f(f(t[0], t[1]),t[2]), ...]


For example, the tab of the partial sums of the integers between 0 (included) and 10 (excluded) is computed by the expression:

       @scan(@+, [$x |$x in (10)])  -> [0,1,3,6,10,15,21,28,36,45]


If t is empty, the results in undef.