map = function(x, f) {
    return(x.map(f))
}
reduce = function(x, f) {
    return(x.reduce(f))
}
reduce_right = function(x, f) {
    return(x.reduceRight(f))
}
filter = function(x, f) {
    return(x.filter(f))
}
walk = function(x, f) {
    return(x.forEach(walk))
}
all = function(x, f) {
    return(x.every(f))
}
any = function(x, f) {
    return(x.some(f))
}
