Pé, the quest for "short" and/or "elegant" solutions to standard-problems in APL is older than PHP and even older than new terminology, such as "eplode", "implode" (I think - but I must admit I do not know how old these terms really are...). Anyway, the early APL guys used the term "idiom" for such "solutions to standard problems that fit in one line of APL". And for some reason, the Finns were especially creative and even started producing a list of these in order to make it easy for newbies. And I find this stuff still useful after 20yrs of doing APL. It is called "FinnAPL" - the Finnish APL idiom library and you can browse it here: http://aplwiki.com/FinnAplIdiomLibrary (BTW, the whole APL-Wiki might be interesting to read...)
You may, however, need to be creative with your wording in order to find solutions ;)
And one warning: FinnAPL only works with "classic" (non-nested) data-structures (nested matrices came with "APL2" which is standard these days), so some of the ways they handle data might no longer be "state-of-the-art". (i.e. back in the "old times", CAT BIRD and DOG would have been represented as a 3x4 array, so "implode" of string-array was a simple as ,array,delimeter
(but you then had the challenge to remove blanks which were inserted for padding.
Anyway, I'm not sure why I wrote all this - just a few thoughts which came to mind when thinking about my start with APL ;-)
Ok, let me also look at the question. When your delimeter is a single character the APL2ish-idiomatic way of handling this would be something like this:
⎕ml←3 ⍝ "migration-level" (only Dyalog APL) to ensure APL2-compatibility
s←' '
A←s,'BIRD',s,'CAT',s,'DOG' ⍝ note that delimeter also used as 1st char!
exploded_string←1↓¨(+\A=s)⊂A ⍝ explode
imploded←∊s,¨exploded_string
A≡imploded ⍝ test for successfull round-trip should return 1