it was the first imperative language supporting closures, after all
Uh, what about lisp?
For those who read the "Foozles" slides posted earlier [0], I must say he nailed this one, on slide 2.
The (MIT) lisp 1.4 manual (ca. 1965) refers to FUNCTION differing from QUOTE in that it handled free variables "correctly"; I take this to mean that at least a primitive form of closure was provided.
Steele's work on Scheme helped Lisp programmers take lexical scoping seriously [1]; these ideas and a method for efficient implementation were attributed to Algol [2]. That lexical scope was available in some dialect of Lisp, even very early on, doesn't surprise me (and according to [3] is the case). But I do think dynamic scoping took a while to "die out" as generally accepted Lisp practice (it does still exist in Common LISP, with a special keyword, IIRC) and that Scheme (late 1970s) helped to effect that.
Moreover, a language that provides SET/SETQ, RPLACA/RPLACD and the PROG feature (including labels and a goto) surely qualifies as imperative?
Haskell has been called the best imperative programming language ever. :-) I mean, Haskell has IORef and friends, right? Jared. [0] http://hope.cs.rice.edu/twiki/pub/WG211/M3Schedule/foozles.pdf [1] Tenth paragraph, this page: http://www.lisp.org/table/Lisp-History.html [2] Steele's Rabbit compiler paper, p.13. See also Steele's Lambda papers [3] Steele and Gabriel, Evolution of Lisp.