func linear_combination(coeffs) {
    var res = ""
    for e,f in (coeffs.kv) {
        given(f) {
            when (1) {
                res += "+e(#{e+1})"
            }
            when (-1) {
                res += "-e(#{e+1})"
            }
            case (.> 0) {
                res += "+#{f}*e(#{e+1})"
            }
            case (.< 0) {
                res += "#{f}*e(#{e+1})"
            }
        }
    }
    res -= /^\+/
    res || 0
}

var tests = [
    %n{1 2 3},
    %n{0 1 2 3},
    %n{1 0 3 4},
    %n{1 2 0},
    %n{0 0 0},
    %n{0},
    %n{1 1 1},
    %n{-1 -1 -1},
    %n{-1 -2 0 -3},
    %n{-1},
]

tests.each { |t|
    printf("%10s -> %-10s\n", t.join(' '), linear_combination(t))
}