> any other language in which a straight concatenation of 3 primitives generates a "flatten" function? Does J count? ;) A quick look here: http://rosettacode.

> any other language in which a straight concatenation of 3 primitives generates a "flatten" function? Does J count? ;) A quick look here: http://rosettacode.org/wiki/Flatten_a_list http://rosettacode.org/wiki/Flatten_a_list seems to suggest that in most languages you need at least ~5 primitives (I'm counting for example pattern matching, 'rec' qualifier in OCaml, named let in Scheme etc. as single language primitives, maybe that's too restricted).