That's questionable. APL doesn't treat functions as first-class values. Its higher-order functions are limited to "operators", i.e. second-order and no higher.
I don't recall SETL, and relational algebra doesn't have functions.
I meant functional in the sense that the 1st-class objects (arrays, sets, relations) are not mutable. (My memory of APL and SETL is fuzzy, so maybe there is some way to alter state, but that certainly isn't the emphasis.)
That's questionable. APL doesn't treat functions as first-class values. Its higher-order functions are limited to "operators", i.e. second-order and no higher.