Clojure科爾馬：如何使用函數中的宏？

Question

我試圖用其中宏函數：

(defentity student 
    (pk :id) 
    (table :student) 
    (entity-fields :id :name :age :class) 
    (database prod)) 

(defn query-student [cond] 
    (select student 
    (where cond))) 

我測試一下：

(select student 
    (where {:age [> 13]})) 

(query-student '{:age [> 13]}) 

它看起來不錯，但這個

(select student 
    (where (or {:age [> 13]} {:class [in ["1" "2" "3"]]}))) 

(query-student '(or {:age [> 13]} {:class [in ["1" "2" "3"]]})) 

不起作用！

Failure to execute query with SQL: 
SELECT "student".* FROM "student" WHERE (or {:age [> 13]} {:class [in ["1" "2" "3"]]}) ::  [] 
PSQLException: 
Message: ERROR: syntax error at or near "or" 
    Location：42 
SQLState: 42601 
Error Code: 0 
PSQLException ERROR: syntax error at or near "or" 
    Location：42 org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse (QueryExecutorImpl.java:2101) 

我想知道爲什麼？有問題？

Answer 1

在科爾馬，where是一個宏，因此你的第二個例子傳遞一個列表文字給它，而不是給宏評估表單的機會。

試着改變你的query-student功能於宏而是沿着這些線路

(defmacro query-student [cond] 
    `(select student 
    (where ~cond))) 

作爲額外的獎勵，你不會需要引用使用宏時的形式：

(query-student (or {:age [> 13]} {:class [in ["1" "2" "3"]]}))

希望這有助於。