clojure for List comprehension

for.clj

user=> (for [file "ABCDEFGH" rank (range 1 9)] (format "%c%d" file rank))
("A1" "A2" "A3" "A4" "A5" "A6" "A7" "A8" "B1" "B2" "B3" "B4" "B5" "B6" "B7" "B8" "C1" "C2" "C3" "C4" "C5" "C6" "C7" "C8" "D1" "D2" "D3" "D4" "D5" "D6" "D7" "D8" "E1" "E2" "E3" "E4" "E5" "E6" "E7" "E8" "F1" "F2" "F3" "F4" "F5" "F6" "F7" "F8" "G1" "G2" "G3" "G4" "G5" "G6" "G7" "G8" "H1" "H2" "H3" "H4" "H5" "H6" "H7" "H8")
user=> (for [rank (range 1 9) file "ABCDEFGH"] (format "%c%d" file rank))
("A1" "B1" "C1" "D1" "E1" "F1" "G1" "H1" "A2" "B2" "C2" "D2" "E2" "F2" "G2" "H2" "A3" "B3" "C3" "D3" "E3" "F3" "G3" "H3" "A4" "B4" "C4" "D4" "E4" "F4" "G4" "H4" "A5" "B5" "C5" "D5" "E5" "F5" "G5" "H5" "A6" "B6" "C6" "D6" "E6" "F6" "G6" "H6" "A7" "B7" "C7" "D7" "E7" "F7" "G7" "H7" "A8" "B8" "C8" "D8" "E8" "F8" "G8" "H8")


from: http://stackoverflow.com/questions/10966142/what-is-the-difference-between-while-and-when-in-clojure
 
:when iterates over the bindings, but only evaluates the body of the loop when the condition is true. 
:while iterates over the bindings and evaluates the body until the condition is false:

(for [x (range 20) :when (not= x 10)] x)
; =>(0 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19)

(for [x (range 20) :while (not= x 10)] x)
; => (0 1 2 3 4 5 6 7 8 9)