SQLite3 haskell createFunction 示例

发布于 2024-10-20 07:35:03 字数 962 浏览 1 评论 0原文

以下是能够创建函数的 SQLite3 Haskell 绑定： http://hackage.haskell.org/packages/archive/sqlite/0.5.1/doc/html/Database-SQLite.html

但我无法使用此功能，我写了像这样的代码：

increment a = a + 1

checkout = do
       handle <- openConnection "test.db"
       ok <- createFunction handle "woot" (IsFunctionHandler increment)

       return $ execStatement handle "SELECT woot(5)";

但它没有编译“不在范围内：数据构造函数‘IsFunctionHandler’”错误

正确的代码是：

module Test where

import Database.SQLite
import Int

increment :: Int64 -> Int64
increment a = a + 1

checkout :: IO (Either String [[Row Value]])
checkout = do
       handle <- openConnection "test.db"
       ok <- createFunction handle "woot" increment

       execStatement handle "SELECT woot(5), woot(7), woot(128)"

感谢HaskellElephant

原文

Here's the SQLite3 Haskell bindings with the ability to create function: http://hackage.haskell.org/packages/archive/sqlite/0.5.1/doc/html/Database-SQLite.html

But I can't get to use this feature, I wrote the code like this:

increment a = a + 1

checkout = do
       handle <- openConnection "test.db"
       ok <- createFunction handle "woot" (IsFunctionHandler increment)

       return $ execStatement handle "SELECT woot(5)";

But it isn't compile with "Not in scope: data constructor `IsFunctionHandler'" error

The correct code is:

module Test where

import Database.SQLite
import Int

increment :: Int64 -> Int64
increment a = a + 1

checkout :: IO (Either String [[Row Value]])
checkout = do
       handle <- openConnection "test.db"
       ok <- createFunction handle "woot" increment

       execStatement handle "SELECT woot(5), woot(7), woot(128)"

Thanks to HaskellElephant

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薆情海 2024-10-27 07:35:03

IsFunctionHandler 是一个类，而不是数据构造函数。它有几个实例< /a> 因此，如果 increment 是 IsFunctionHandler 的实例（在本例中就是这样），您应该能够编写：

createFunction handle "woot" increment

IsFunctionHandler is a class, not a data constructor. It has several instances so if increment is an instance of IsFunctionHandler, wich it in this case is, you should be able to write: