Inverse of `split` function: `join` a string using a delimeter

Question

IN Red and Rebol(3), you can use the split function to split a string into a list of items:

>> items: split {1, 2, 3, 4} {,}
== ["1" " 2" " 3" " 4"]

What is the corresponding inverse function to join a list of items into a string? It should work similar to the following:

>> join items {, }
== "1, 2, 3, 4"

Answer 1

There is an old modification of rejoin doing that

rejoin: func [
    "Reduces and joins a block of values - allows /with refinement." 
    block [block!] "Values to reduce and join" 
    /with join-thing "Value to place in between each element" 
][ 
    block: reduce block 
    if with [ 
        while [not tail? block: next block][ 
            insert block join-thing 
            block: next block
       ] 
       block: head block 
    ] 
    append either series? first block [ 
       copy first block
    ] [
       form first block
    ] 
    next block 
]

call it like this rejoin/with [..] delimiter

But I am pretty sure, there are other, even older solutions.