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.

Answer 2

There's no inbuild function yet, you have to implement it yourself:

>> join: function [series delimiter][length: either char? delimiter [1][length? delimiter] out: collect/into [foreach value series [keep rejoin [value delimiter]]] copy {} remove/part skip tail out negate length length out]
== func [series delimiter /local length out value][length: either char? delimiter [1] [length? delimiter] out: collect/into [foreach value series [keep rejoin [value delimiter]]] copy "" remove/part skip tail out negate length length out]
>> join [1 2 3] #","
== "1,2,3"
>> join [1 2 3] {, }
== "1, 2, 3"

per request, here is the function split into more lines:

join: function [
    series 
    delimiter
][
    length: either char? delimiter [1][length? delimiter] 
    out: collect/into [
        foreach value series [keep rejoin [value delimiter]]
    ] copy {} 
    remove/part skip tail out negate length length 
    out
]

Answer 3

Following function works:

myjoin: function[blk[block!] delim [string!]][
    outstr: ""
    repeat i ((length? blk) - 1)[
        append outstr blk/1
        append outstr delim
        blk: next blk ]
    append outstr blk ]

probe myjoin ["A" "B" "C" "D" "E"] ", "

Output:

"A, B, C, D, E"