Indeed the primary usage was text and string manipulation; it had a huge following in the 70s and 80s in the humanities. However, like with most languages, all the bases are covered for complex functions, mathematics, etc; it just never got as much traction in those spaces. Far as I know it was the first language to use associative-arrays, it also supports backtracking (like prolog), and meta-programming (code generation during runtime), map functions, lambda like functions, etc. It really had it all!