将使用 2 个序列的 Seq.map 应用于采用 2 个参数的方法
我正在编写一个快速的数据库性能测试，并选择了 F#，这样我就可以获得更多练习。
我创建了一个方法 measureSelectTimes，其签名为 Guid list * Guid list -> IDb命令->时间跨度 * 时间跨度。
然后，我称之为：
let runTests () =
let sqlCeConn : IDbConnection = initSqlCe() :> IDbConnection
let sqlServerConn : IDbConnection = initSqlServer() :> IDbConnection
let dbsToTest = [ sqlCeConn; sqlServerConn ]
let cmds : seq<IDbCommand> = dbsToTest |> Seq.map initSchema
let ids : seq<Guid list * Guid list> = cmds |> Seq.map loadData
let input = Seq.zip ids cmds
let results = input |> Seq.map (fun i -> measureSelectTimes (fst i) (snd i))
// ...
我已经用类型明确注释了以进行澄清。
我不知道如何在没有 lambda 的情况下调用 measureSelectTimes 。我想将 ids 部分应用到它，如下所示： ids |> Seq.mapmeasureSelectTimes 但我不知道如何处理所得到的部分应用函数，然后映射到 cmds 上。这个的语法是什么？
I'm writing a quick DB perf test, and chose F# so I can get more practice.
I've created a method, measureSelectTimes, which has the signature Guid list * Guid list -> IDbCommand -> TimeSpan * TimeSpan.
Then, I call it:
let runTests () =
let sqlCeConn : IDbConnection = initSqlCe() :> IDbConnection
let sqlServerConn : IDbConnection = initSqlServer() :> IDbConnection
let dbsToTest = [ sqlCeConn; sqlServerConn ]
let cmds : seq<IDbCommand> = dbsToTest |> Seq.map initSchema
let ids : seq<Guid list * Guid list> = cmds |> Seq.map loadData
let input = Seq.zip ids cmds
let results = input |> Seq.map (fun i -> measureSelectTimes (fst i) (snd i))
// ...
I've annotated explicitly with types to clarify.
What I can't figure out is how to call measureSelectTimes without the lambda. I'd like to partially apply the ids to it like this: ids |> Seq.map measureSelectTimes but then I don't know what to do with the resulting partially applied functions to then map onto the cmds. What's the syntax for this?
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您可以使用
Seq.map2：或者
You can use
Seq.map2:Or
您的
measureSelectTimes函数将两个参数作为单独的参数，但您需要一个将它们作为元组的函数。一种选择是仅更改函数以采用元组（如果对参数进行元组化是合乎逻辑的）。或者，您可以编写一个组合器，将带有两个参数的函数转换为带有元组的函数。这通常称为 uncurry ，它存在于某些函数式语言中：
然后你可以这样写：
对于像这样的简单使用来说，这看起来没问题，但我认为在 F# 中过多使用组合器并不是一个好主意因为它使得经验不足的函数式程序员难以阅读代码。我可能会写这样的东西（因为我发现这样更具可读性）：
Your
measureSelectTimesfunction takes two arguments as separate arguments, but you instead need a function that takes them as a tuple. One option is to just change the function to take a tuple (if it is logical for the arguments to be tupled).Alternative, you can write a cobinator that turns a function taking two arguments into a function taking tuple. This is usually called
uncurryand it exists in some functional language:Then you can write:
This looks okay for a simple use like this, but I think that using combinators too much in F# is not a good idea as it makes code difficult to read for less experienced functional programmers. I would probably write something like this (because I find that more readable):
一种方法是将
measureSelectTimes的签名更改为然后您可以将
map调用更改为One approach is to change the signature of
measureSelectTimestoThen you can change the
mapcall to