What is the origin of “banana brackets”?

"Banana" brackets are used to denote catamorphisms:

Another notation found in the literature is .

These symbols are very similar to the composition of a $$($$ and a $$|$$, is this similarity more than coincidence? I.e. is there some motivation where they represent the same as $$|...|$$ followed by $$(...)$$ ?

The later style using $$($$ and $$|$$ seems to be a typographic practicality, and is used by Malcolm himself in another publication the same year: