Breaking out of a recursive function

I'm walking through a set of nested blocks and want to stop the walk when I've found the value I'm looking for.

For reasons that are beyond the scope of this question, I can't use PARSE for this particular problem, nor use FOREACH as the looper:

walk: func [series [block!] criteria [block!]][
    use [value] compose/deep [
        while [not tail? series][
            value: pick series 1

            either block? value [
                walk value criteria
            ][
                (to paren! criteria)
            ]

            series: next series
        ]
    ]
]

I'd like to break out if I find this specific value.

walk [a [b c [d e] f] g] [if value = 'e [return value]]
; returns 'e

However, I'd also like to do operations that don't break out:

walk [a [b c [d e] f] g] [
    collect [if find [c e] value [keep value]]
]
; returns [c e]

Would like to try and solve this for any of the Rebol flavours including Red. Any thoughts as to efficiency (reason I use a block instead of a function), etc. would be welcome too.