Question

我想用一个宏来处理seq参数，但我不知道怎么做！

e.g：

(defmacro create-table-def
  [s]
  `(let [ks# (keys (struct-map ~s))
         sql# (map (fn [p#] (str (name p#) " varchar(20) ")) ks#)]
     (str "create-table " '~s " ( "
          (apply str (interleave seq# ", ")) " ) ") ))

我有多个参数调用这个宏，但不使用map（map create-table-def ps）或者reduce，我应该怎么做才能处理。

我使用宏，因为我想知道参数符号。

Answer 1

我想出了这个与你的版本非常接近的版本：

(defmacro create-table-def [table-name key-val-map]
  (let [sql-part1 (vector "create table " 
      (name table-name)
      "(")
 sql-pre-part2 (apply vector 
        (map #(str (name (first %)) 
     " " 
     (second %)) 
      key-val-map))
 sql-part2 (butlast (interleave sql-pre-part2 (repeat ", ")))
 sql-part3 [");"]]
    (apply str (concat sql-part1 sql-part2 sql-part3))))

(create-table-def my-table {foo "varchar(20)" bar "int"})
;"create table my-table(foo varchar(20), bar int);"

如果你确实需要传递seq，你可以这样做：

(defmacro create-table-def2 [[name & pairs]]
  `(create-table-def ~name ~(apply array-map pairs)))

(create-table-def2 [my-table foo "varchar(20)" bar "int"])
;"create table my-table(foo varchar(20), bar int);"

或者就像直接论点一样：

(defmacro create-table-def3 [name & pairs]
  `(create-table-def ~name ~(apply array-map pairs)))

(create-table-def3 my-table foo "varchar(20)" bar "int")
;"create table my-table(foo varchar(20), bar int);"

更直接地关注解决方案，然而，（ab）使用地图的印刷表示：

(use '[clojure.contrib.string :as str-utils])
(defmacro table-def [tname & things]
  (str-utils/join " " 
    ["create-table" (name tname) "("
     (str-utils/drop 1 
             (str-utils/chop 
              (print-str (apply array-map things))))
     ");"]))
(table-def my-table foo "varchar(20)" bar "int")
;"create-table my-table ( foo varchar(20), bar int );"

宏如何处理sql像fn使用map

1 个答案: