What's the fastest/most efficient way to count

Question

Given a string string, what is the fastest/most-efficient way to count lines therein? Will accept best answers for any flavour of Rebol. I've been working under the assumption that the parse [some [thru]] combination was the fastest way to traverse a string, but then I don't know that for certain, hence turning to SO:

count-lines: func [string [string!] /local count][
    parse/all string [
        (count: 1) some [thru newline (count: count + 1)]
    ]
    count
]

Or:

count-lines: func [string [string!] /local count][
    count: 0
    until [
        count: count + 1
        not string: find/tail string newline
    ]
    count
]

And how about counters? How efficient is repeat?

count-lines: func [string [string!]][
    repeat count length? string [
        unless string: find/tail string newline [
            break/return count
        ]
    ]
]

Update: line count goes by the Text Editor principle:

An empty document still has a line count of one. So:

>> count-lines ""
== 1
>> count-lines "^/"
== 2

Answer 1

Here is the best for me:

temp: read/lines %mytext.txt
length? temp

Answer 2

count-lines: func [
    str
    /local sort-str ][
sort-str: sort join str "^/"
1 + subtract index? find/last sort-str "^/" index? find sort-str "^/"
]

Answer 3

Why no one came with the simplest solution I wonder :)

t: "abc^/de^/f^/ghi"
i: 0 until [i: i + 1 not t: find/tail t newline] i
== 4

Not sure about the performance but I think it's quite fast, as UNTIL and FIND are natives. WHILE could be used as well.

i: 1 while [t: find/tail t newline] [i: i + 1] i
== 4

Just need to check for empty string. And if it would be a function, argument series needs to be HEADed.