with javascript_semantics
function linear_combination(sequence f)
    string res = "", fmt
    for i,e in f do
        if e!=0 then
            integer l = length(res)
            if abs(e)=1 then
                res &= iff(e<0?"-":iff(l?"+":""))
            else
                fmt = iff(e>0 and l?"+%d*":"%d*")
                res &= sprintf(fmt,e)
            end if
            res &= sprintf("e(%d)",i)
        end if
    end for
    if res="" then res = "0" end if
    return res
end function

constant tests = {{1,2,3},{0,1,2,3},{1,0,3,4},{1,2,0},{0,0,0},
                  {0},{1,1,1},{-1,-1,-1},{-1,-2,0,-3},{-1}}
for t in tests do
    printf(1,"%12v -> %s\n",{t, linear_combination(t)})
end for