(defmacro cond->>
"Takes an expression and a set of test/form pairs. Threads expr (via ->>)
through each form for which the corresponding test expression
is true. Note that, unlike cond branching, cond->> threading does not short circuit
after the first true test expression."
{:added "1.5"}
[expr & clauses]
(assert (even? (count clauses)))
(let [g (gensym)
steps (map (fn [[test step]] `(if ~test (->> ~g ~step) ~g))
(partition 2 clauses))]
`(let [~g ~expr
~@(interleave (repeat g) (butlast steps))]
~(if (empty? steps)
g
(last steps)))))