以下代码失败：
open Microsoft.FSharp.Reflection
open Microsoft.FSharp.Quotations
let (empty,cons) =
FSharpType.GetUnionCases(typeof<List<_>>)
|> (fun cases ->
cases |> Array.find (fun c -> c.Name = "Empty"),
cases |> Array.find (fun c -> c.Name = "Cons"))
let valuesToList values =
values
|> List.map (fun v -> Expr.Value(v))
|> List.fold
(fun l v -> Expr.NewUnionCase(cons, [v;l]))
<@@ List.empty<int> @@>
[1;2;3]
|> valuesToList
除外：
System.ArgumentException: Type mismatch when building 'sum': incorrect argument type for an F# union. Expected 'System.Object', but received type 'System.Int32'.
如何指定Cons union case的泛型参数类型？
答案 0 :(得分：3)
问题在于.wrapper {
width: 80%;
margin: 1em auto;
overflow: hidden;
}
.wrapper div {
float: left;
width: 50%;
min-height: 100px;
}
.wrapper div:nth-child(1) {
background: #f66;
width: 100%;
min-height: 100px;
}
.wrapper div:nth-child(2) {
background: #6f6;
}
.wrapper div:nth-child(3) {
background: #66f;
}
.wrapper div:nth-child(4) {
background: #ff6;
}
.wrapper div:only-child {
width: 100%;
min-height: 200px;
}
.wrapper div:nth-child(2):nth-last-child(1) {
width: 100%;
min-height: 100px;
}
.wrapper div:nth-child(3):nth-last-child(1) {
width: 50%;
min-height: 100px;
}
.wrapper div:nth-child(2):nth-last-child(2) {
width: 50%;
min-height: 100px;
}
.wrapper div:nth-child(1):nth-last-child(4) {
width: 50%;
min-height: 100px;
}
.wrapper div:nth-child(2):nth-last-child(3) {
width: 50%;
min-height: 100px;
}
.wrapper div:nth-child(3):nth-last-child(1) {
width: 50%;
min-height: 100px;
}
。通配符被推断为GetUnionCases(typeof<List<_>>)。因此错误
预期＆＃39; System.Object＆＃39;，但收到类型＆＃39; System.Int32＆＃39;。
这是一个有效的版本。
obj