If he wants to learn such an obscure (popularity-wise) language, he's probably better off using a popular (relatively), well-documented, well-supported (libraries) and stable dialect such as Common Lisp or Scheme.
I've just started learning Lisp and I find Arc fun. Hence, the suggestion. There are some nice people like coconutrandom, CatDancer, palsecam, zck and conanite who are active and helpful on the forum e.g. http://arclanguage.org/item?id=10554. The unofficial code repository Anarki is pretty good too.
