user=> (defmacro foreach [[sym coll] & body]  `(loop [coll# ~coll]     (when-let [[~sym & xs#] (seq coll#)]       ~@body       (recur xs#))))#'user/foreachuser=>user=> (foreach [x [1 2 3]]  (println x))123niluser=>

user=> (defmacro dbg[x] `(let [x# ~x] (println '~x "=" x#) x#)) user=> (def x 5)user=> (def lst '(a b c))user=> `(fred x ~x lst ~@lst 7 8 :nine)    (user/fred user/x 5 user/lst a b c 7 8 :nine) user=> `(abc ~(symbol (str "i" "s" \- "cool")))(user/abc is-cool) user=>  `(max ~@(shuffle (range 10)))(clojure.core/max 8 7 1 9 0 6 4 2 3 5)

user=> '(foo bar)(foo bar)user=> `(foo bar)(user/foo user/bar)

user=> (defmacro debug [x] `(println ">>" '~x ":" ~x  x))#'user/debuguser=> (let [a 10] (debug a))CompilerException java.lang.RuntimeException: No such var: user/x, compiling:(NO_SOURCE_PATH:72)user=>

user=>  (defmacro debug [x] `(println ">>" '~x ":" ~x  23))#'user/debuguser=> (let [a 10] (debug a))>> a : 10 23niluser=>

' 的实现dispatchMacros['\''] = new VarReader(); public static class VarReader extends AFn{     public Object invoke(Object reader, Object quote) {          PushbackReader r = (PushbackReader) reader;          Object o = read(r, true, null, true);          return RT.list(THE_VAR, o);     }}    `的实现macros['`'] = new SyntaxQuoteReader(); public static class SyntaxQuoteReader extends AFn{ // 代码省略........} ~的实现 macros['~'] = new UnquoteReader(); static class UnquoteReader extends AFn{     public Object invoke(Object reader, Object comma) {          PushbackReader r = (PushbackReader) reader;          int ch = read1(r);          if(ch == -1)               throw Util.runtimeException("EOF while reading character");          if(ch == '@')               {               Object o = read(r, true, null, true);               return RT.list(UNQUOTE_SPLICING, o);               }          else               {               unread(r, ch);               Object o = read(r, true, null, true);               return RT.list(UNQUOTE, o);               }     }}

user=>  (let [x 9, y '(- x)]  (println 0 y)  (println 1 `y)  (println 2 ``y)  (println 3 ```y)  ;(println 4 ~y)  (println 5 `~y)  (println 6 ``~y)  (println 7 ``~~y))0 (- x)1 user/y2 (quote user/y)3 (clojure.core/seq (clojure.core/concat (clojure.core/list (quote quote)) (clojure.core/list (quote user/y))))5 (- x)6 user/y7 (- x)niluser=>

user=> (source macroexpand)(defn macroexpand  "Repeatedly calls macroexpand-1 on form until it no longer  represents a macro form, then returns it.  Note neither  macroexpand-1 nor macroexpand expand macros in subforms."  {:added "1.0"   :static true}  [form]    (let [ex (macroexpand-1 form)]      (if (identical? ex form)        form        (macroexpand ex))))niluser=> (source macroexpand-1)(defn macroexpand-1  "If form represents a macro form, returns its expansion,  else returns form."  {:added "1.0"   :static true}  [form]    (. clojure.lang.Compiler (macroexpand1 form)))niluser=>

user=> `(x#)(x__6__auto__) ;;;定义dbguser=> (defmacro dbg[x] `(let [x# ~x] (println '~x "=" x#) x#))#'user/dbguser=> (defn pythag [x,y] (*(* x x) (* y y)))#'user/pythaguser=> (pythag  5 6 )900user=> (defn pythag [x,y] (dbg(* (dbg (* x x)) (dbg (* y y)))))#'user/pythaguser=> (pythag  5 6 )(* x x) = 25(* y y) = 36(* (dbg (* x x)) (dbg (* y y))) = 900900

user=> ( -> 25 Math/sqrt int list)(5)user=> ( ->> 25 Math/sqrt int list)(5)user=> (source ->)(defmacro ->  "Threads the expr through the forms. Inserts x as the  second item in the first form, making a list of it if it is not a  list already. If there are more forms, inserts the first form as the  second item in second form, etc."  {:added "1.0"}  ([x] x)  ([x form] (if (seq? form)              (with-meta `(~(first form) ~x ~@(next form)) (meta form))              (list form x)))  ([x form & more] `(-> (-> ~x ~form) ~@more)))niluser=> (source ->>)(defmacro ->>  "Threads the expr through the forms. Inserts x as the  last item in the first form, making a list of it if it is not a  list already. If there are more forms, inserts the first form as the  last item in second form, etc."  {:added "1.1"}  ([x form] (if (seq? form)              (with-meta `(~(first form) ~@(next form)  ~x) (meta form))              (list form x)))  ([x form & more] `(->> (->> ~x ~form) ~@more)))niluser=>