symbolic math - Force evaluate index expression before passing to sum() -

i want write (somehow) enhanced sum function takes number of indices @ once, cannot understand how work. here have:

(%i1) nsum(indexes, expr) :=           if indexes = []           expr           else nsum(rest(indexes), sum(expr, first(indexes),1, n)) $  (%i2) nsum([i,j], i+j), nouns;       sum: index must symbol; found intosym(first(indexes))       #0: nsum(indexes=[k,j],expr=k+j) 

i think fixed forcing maxima expand first(indexes) symbol before passing sum function. tried ''(...) , ev(..., nouns), without success.

after reading , trying came following solution uses apply function pre-evaluate arguments sum:

nsum(indexes, expr) :=     if indexes = []     expr     else nsum(rest(indexes), apply(sum, ['expr, indexes[1], 1, n])) $ 

upd1:
unfortunately, there wrong above code, works relatively simple expressions. in case straightforward approach works fine nsum fails:

(%i1) rot[i](f) := sum(sum(sum(sum(       g[r,i]*g[q,j]*w[i,j,k]*('diff(f[k], y[q]) + sum(k[k,q,m]*f[m], m, 1, n)),         r, 1, n),         j, 1, n),         k, 1, n),         q, 1, n) $  (%i2) rot2[i](f) := nsum( [r,j,k,q],         g[r,i]*g[q,j]*w[i,j,k]*('diff(f['k], y[q]) + sum(k[k,q,m]*f[m], m, 1, n))) $  (%i3) rot[1](f); (%o3) ... yelds result.  (%i4) rot2[1](f); apply: subscript must integer; found: k lambda([i,j],diff(ys[i],x[j]))(i=k,j=1) 

upd2:

the code works indeed. 'k accidentally left in rot2 definition instead of k.