使用计算表达式组成引用的函数
我环顾四周，努力寻找这个问题的答案；我确信有一个显而易见的答案，但我就是找不到它；或者我遇到了在使用计算表达式时无法通过的引号限制。
基本上，我希望使用计算F#工作流处理如下定义的引用的lambda。当试图将这些工作流组合在一起时，问题就出现了。理想情况下，我希望使用let！语法将工作流<‘Env 'Result>实例组合在一起。
type Workflow<'Env, 'Result> = Expr<'Env -> 'Result>
type WorkflowSource<'Env, 'Result> = 'Env -> 'Result
type WorkflowBuilder() =
member x.Bind
(workflow: WorkflowSource<'Env, 'OldResult>,
selector: 'OldResult -> WorkflowSource<'Env, 'NewResult>) : WorkflowSource<'Env, 'NewResult> =
(fun env -> (selector (workflow env) env))
member x.Bind
(workflow: Workflow<'Env, 'OldResult>,
selector: 'OldResult -> WorkflowSource<'Env, 'NewResult>)
: Workflow<'Env, 'NewResult> =
<@ (fun env -> (selector ((%workflow) env) env)) @>
// This bind is where the trouble is
member x.Bind
(workflow: WorkflowSource<'Env, 'OldResult>,
selector: 'OldResult -> Workflow<'Env, 'NewResult>)
: Workflow<'Env, 'NewResult> =
<@ fun env ->
let newResultWorkflow = %(selector (workflow env))
newResultWorkflow env @>
member __.Return(x) = fun env -> x
member __.ReturnFrom(x : WorkflowSource<_, _>) = x
member __.Quote(x : Expr<WorkflowSource<_, _>>) : Workflow<_, _> = x
let workflow = new WorkflowBuilder()第三个bind成员告诉我编译器错误：“变量"env”绑定在引号中，但用在一个切片表达式中“，这有点道理。问题是我如何绕过它。我将上面的定义定义为尝试让下面的简单情况正常工作。
let getNumber (env: EnvironmentContext) = (new Random()).Next()
let workflow1 = workflow {
let! randomNumber = getNumber
let customValue = randomNumber * 10
return (globalId * customValue)
}
// From expression to non expression bind case
let workflow2a = workflow {
let! workflow1 = workflow1
let! randomNumber = getNumber
return (randomNumber + workflow1)
}
// From non-expression to expression bind case
let workflow2 = workflow {
let! randomNumber = getNumber
let! workflow1 = workflow1
return (randomNumber + workflow1)
}只是想知道我想要实现的是不是可能，还是我做错了什么？是否有可能在捕获最终引用表达式中的用户函数的同时，让上述简单的情况正常工作？
编辑:考虑到Tomas的回答，我也尝试了不使用WorkflowSource类型。错误: System.InvalidOperationException:在Microsoft.FSharp.Core.ExtraTopLevelOperators.SpliceExpressionT中不允许使用'%‘或'%%’的第一类
type WorkflowBuilder() =
member x.Bind
(workflow: Workflow<'Env, 'OldResult>,
selector: 'OldResult -> Workflow<'Env, 'NewResult>)
: Workflow<'Env, 'NewResult> =
fun env -> <@ %(selector (%(workflow env)) env) @>
member __.Return(x) = fun Env -> <@ x @>
member __.ReturnFrom(x: Workflow<_, _>) = x
member __.Quote(expr: Expr<Workflow<'Env, 'Result>>) = expr
// This run method fails
member __.Run(x : Expr<Workflow<'Env, 'Result>>) : Workflow<'Env, 'Result> = fun (env: Expr<'Env>) -> <@ %((%x) env) @>
let workflow = new WorkflowBuilder()
// Env of type int for testing
let getRandomNumber (kernel: Expr<int>) = <@ (new Random()).Next() @>
let workflow1 = workflow {
let! randomNumber = getRandomNumber
let otherValue = 2
let! randomNumber2 = getRandomNumber
return randomNumber + otherValue + randomNumber2
}
// This fails due to quotation slicing issue
workflow1 <@ 0 @>回答 1
Stack Overflow用户
发布于 2015-09-15 20:49:24
这只是一个想法的粗略草图，但我认为如果您不将工作流表示为引用的函数，而是将其表示为采用引用的环境并返回引用的结果的函数，则可以更进一步：
type Workflow<'Env, 'Result> = Expr<'Env> -> Expr<'Result>然后，您肯定可以实现所有的绑定：
member x.Bind
(workflow: WorkflowSource<'Env, 'OldResult>,
selector: 'OldResult -> WorkflowSource<'Env, 'NewResult>) : WorkflowSource<'Env, 'NewResult> =
(fun env -> (selector (workflow env) env))
member x.Bind
(workflow: Workflow<'Env, 'OldResult>,
selector: 'OldResult -> WorkflowSource<'Env, 'NewResult>)
: Workflow<'Env, 'NewResult> =
fun env -> <@ selector %(workflow env) %env @>
// This bind is where the trouble is
member x.Bind
(workflow: WorkflowSource<'Env, 'OldResult>,
selector: 'OldResult -> Workflow<'Env, 'NewResult>)
: Workflow<'Env, 'NewResult> =
fun env -> <@ %(selector (workflow %env) env) @>也就是说，我认为这还不是你需要的全部-编译器似乎忽略了Quote中的代码，所以即使我们添加了将WorkflowSource转换为Workflow的引号，你仍然会得到错误，因为有Expr<WorkflowSource<_>>值-但我认为另一个绑定重载可能会解决这个问题。
member __.Quote(x : Expr<WorkflowSource<_, _>>) : Workflow<_, _> =
fun env -> <@ (%x) %env @>https://stackoverflow.com/questions/32585674
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