I can't figure out this F# error message

Question

The error messages generated by the F# compiler are sometimes confusing. For example:

open Deedle
let inds = [1;   2;  6;  8; 11; 12]
let vals = [10; 20; 30; 40; 50; 60]
let siv = Series(inds, vals)
let fbminmax b (s: Series<float, float>) =
    if b then (Seq.min s.Values) else (Seq.max s.Values)
let sgi =
    siv
    |> Series.groupInto (fun i _ -> i % 2 = 0) fbminmax
printfn "%A" <| sgi
// error FS0001: Type mismatch. Expecting a
//    'bool -> Series<int,int> -> 'a'    
// but given a
//    'bool -> Series<int,int> -> float'    
// The type 'float' does not match the type 'int'

I understand there is an error (the code works fine with Series<int,int> replacing Series<float,float> in the definition of fbminmax). And I understand that a

'bool -> Series<int,int> -> 'a'

was expected. But I do not understand why the compiler says that it was given a

'bool -> Series<int,int> -> float'

when it was given fbminmax, which is a

'bool -> Series<float,float> -> float'

Moreover, if the compiler had indeed been given a

'bool -> Series<int,int> -> float'

as it claimed it did that should have been Ok with float playing the role of 'a.

Can someone provide some insight on what is going on?

Answer 1

编译器错误消息确实有点神秘。解决方案：通用它： - ）

let fbminmax b (s: Series<'T, 'T>) =
    if b then (Seq.min s.Values) else (Seq.max s.Values)

最后的问题是您指定了fbminmax b (s: Series<float, float>)，但是向其中提供了一系列int。

Answer 2

只是一个猜测，但是当你尝试使你的int浮动时，编译器会说些什么？

从：

let inds = [1;   2;  6;  8; 11; 12]
let vals = [10; 20; 30; 40; 50; 60]

为：

let inds = [1.0;   2.0;  6.0;  8.0; 11.0; 12.0]
let vals = [10.0; 20.0; 30.0; 40.0; 50.0; 60.0]