Some comma quibbling in Rebol

comma1.r3

Rebol []

comma-quibbling: func [block] [
    rejoin [
        "^{"
    
        to-string use [s] [
            s: copy block
            s: next s
            forskip s 2 [insert s either tail? next s [" and "] [", "]]
            s: head s
        ]
            
        "^}"
    ]       
]       

foreach t [[] [ABC] [ABC DEF] [ABC DEF G H]] [
    print comma-quibbling t
]

comma2.r3

Rebol []

; a recursive version
    
comma-quibbling: func [block /local sub-quibble] [
    sub-quibble: func [words] [
        switch/default length? words [
            0  [""] 
            1  [words/1]
            2  [rejoin [words/1 " and " words/2]]
        ][  
            insert words rejoin [take words ", " take words]
            sub-quibble words
        ]
    ]       

    rejoin [ "^{" sub-quibble copy block "^}" ]
]
    
test: [[] [ABC] [ABC DEF] [ABC DEF G H]]
foreach t test [print comma-quibbling t]