Koka for loops

for.kk

effect leq<a> {
    fun leq(first: a, second: a) : bool
}

fun for(
    from: a, 
    incr: a -> <div,leq<a>|e> a, 
    to: a, 
    do: () -> <div,leq<a>|e> ()
) : <div,leq<a>|e> () {
    if (from.leq(to)) then {
        do();
        for(from.incr, incr, to, do)
    } else ()
}

fun using-for () {
    var something := 0
    with fun leq(first: int, second: int) {first <= something}
    for(0, fn (a) {a+1}, 10) {
        something := something + 1
    }

    var something-else := "a"
    with fun leq(first: string, second: string) {first <= second}
    for("", fn (a) {a+"a"}, "aaaaaaa") {
        something-else := something-else + "a"
    }

    (something, something-else)
}

But don't you need a generic function parameter for each "type class" you're handling? Or is there a way that your one generic function argument can be row typed?