我正试图围绕FSharpPlus的trySscanf创建一个活动模式Scan，以便以下各项工作：
let res = // res = 42
match "Hello 42 World" with
| Scan "Hello %i World" n -> n
我理解不完全活动模式的工作方式，我只需要返回一个选项，trySscanf已经返回了一个选项。所以我尝试了以下操作：
let (|Scan|_|) = trySscanf
当这不起作用时，我尝试了一个更明确的
let (|Scan|_|) pattern input = trySscanf pattern input
它们都因以下编译错误而失败：
Type constraint mismatch when applying the default type 'obj' for a type inference variable. No overloads match for method 'TryParseArray'.
Known return type: (string [] -> obj option)
Known type parameters: < obj , Internals.TryParseArray >
Available overloads:
- static member Internals.TryParseArray.TryParseArray : ^t * obj -> (string [] -> ^t option) when (Control.TryParse or ^t) : (static member TryParse : ^t * Control.TryParse -> (string -> ^t option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2' * 't3 * 't4 * 't5 * 't6 * 't7) * Internals.TryParseArray -> (string [] -> ( ^a7 * ^a8 * ^a9 * ^a10 * ^a11 * ^a12 * ^a13) option) when (Control.TryParse or ^a7) : (static member TryParse : ^a7 * Control.TryParse -> (string -> ^a7 option)) and (Control.TryParse or ^a8) : (static member TryParse : ^a8 * Control.TryParse -> (string -> ^a8 option)) and (Control.TryParse or ^a9) : (static member TryParse : ^a9 * Control.TryParse -> (string -> ^a9 option)) and (Control.TryParse or ^a10) : (static member TryParse : ^a10 * Control.TryParse -> (string -> ^a10 option)) and (Control.TryParse or ^a11) : (static member TryParse : ^a11 * Control.TryParse -> (string -> ^a11 option)) and (Control.TryParse or ^a12) : (static member TryParse : ^a12 * Control.TryParse -> (string -> ^a12 option)) and (Control.TryParse or ^a13) : (static member TryParse : ^a13 * Control.TryParse -> (string -> ^a13 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2' * 't3 * 't4 * 't5 * 't6) * Internals.TryParseArray -> (string [] -> ( ^a6 * ^a7 * ^a8 * ^a9 * ^a10 * ^a11) option) when (Control.TryParse or ^a6) : (static member TryParse : ^a6 * Control.TryParse -> (string -> ^a6 option)) and (Control.TryParse or ^a7) : (static member TryParse : ^a7 * Control.TryParse -> (string -> ^a7 option)) and (Control.TryParse or ^a8) : (static member TryParse : ^a8 * Control.TryParse -> (string -> ^a8 option)) and (Control.TryParse or ^a9) : (static member TryParse : ^a9 * Control.TryParse -> (string -> ^a9 option)) and (Control.TryParse or ^a10) : (static member TryParse : ^a10 * Control.TryParse -> (string -> ^a10 option)) and (Control.TryParse or ^a11) : (static member TryParse : ^a11 * Control.TryParse -> (string -> ^a11 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2' * 't3 * 't4 * 't5) * Internals.TryParseArray -> (string [] -> ( ^a5 * ^a6 * ^a7 * ^a8 * ^a9) option) when (Control.TryParse or ^a5) : (static member TryParse : ^a5 * Control.TryParse -> (string -> ^a5 option)) and (Control.TryParse or ^a6) : (static member TryParse : ^a6 * Control.TryParse -> (string -> ^a6 option)) and (Control.TryParse or ^a7) : (static member TryParse : ^a7 * Control.TryParse -> (string -> ^a7 option)) and (Control.TryParse or ^a8) : (static member TryParse : ^a8 * Control.TryParse -> (string -> ^a8 option)) and (Control.TryParse or ^a9) : (static member TryParse : ^a9 * Control.TryParse -> (string -> ^a9 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2' * 't3 * 't4) * Internals.TryParseArray -> (string [] -> ( ^a4 * ^a5 * ^a6 * ^a7) option) when (Control.TryParse or ^a4) : (static member TryParse : ^a4 * Control.TryParse -> (string -> ^a4 option)) and (Control.TryParse or ^a5) : (static member TryParse : ^a5 * Control.TryParse -> (string -> ^a5 option)) and (Control.TryParse or ^a6) : (static member TryParse : ^a6 * Control.TryParse -> (string -> ^a6 option)) and (Control.TryParse or ^a7) : (static member TryParse : ^a7 * Control.TryParse -> (string -> ^a7 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2' * 't3) * Internals.TryParseArray -> (string [] -> ( ^a3 * ^a4 * ^a5) option) when (Control.TryParse or ^a3) : (static member TryParse : ^a3 * Control.TryParse -> (string -> ^a3 option)) and (Control.TryParse or ^a4) : (static member TryParse : ^a4 * Control.TryParse -> (string -> ^a4 option)) and (Control.TryParse or ^a5) : (static member TryParse : ^a5 * Control.TryParse -> (string -> ^a5 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : ('t1 * 't2) * Internals.TryParseArray -> (string [] -> ( ^a2 * ^a3) option) when (Control.TryParse or ^a2) : (static member TryParse : ^a2 * Control.TryParse -> (string -> ^a2 option)) and (Control.TryParse or ^a3) : (static member TryParse : ^a3 * Control.TryParse -> (string -> ^a3 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : Internals.Id<'t1> * Internals.TryParseArray -> (string [] -> Internals.Id< ^a1> option) when (Control.TryParse or ^a1) : (static member TryParse : ^a1 * Control.TryParse -> (string -> ^a1 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : Tuple< ^t1> * Internals.TryParseArray -> (string [] -> Tuple< ^t1> option) when (Control.TryParse or ^t1) : (static member TryParse : ^t1 * Control.TryParse -> (string -> ^t1 option)) // Argument at index 1 doesn't match
- static member Internals.TryParseArray.TryParseArray : t: ^t * Internals.TryParseArray -> (string [] -> ^t option) when ^t : (member get_Item1 : ^t -> ^t1) and ^t : (member get_Item2 : ^t -> ^t2) and ^t : (member get_Item3 : ^t -> ^t3) and ^t : (member get_Item4 : ^t -> ^t4) and ^t : (member get_Item5 : ^t -> ^t5) and ^t : (member get_Item6 : ^t -> ^t6) and ^t : (member get_Item7 : ^t -> ^t7) and ^t : (member get_Rest : ^t -> ^tr) and (Control.TryParse or ^t1) : (static member TryParse : ^t1 * Control.TryParse -> (string -> ^t1 option)) and (Control.TryParse or ^t2) : (static member TryParse : ^t2 * Control.TryParse -> (string -> ^t2 option)) and (Control.TryParse or ^t3) : (static member TryParse : ^t3 * Control.TryParse -> (string -> ^t3 option)) and (Control.TryParse or ^t4) : (static member TryParse : ^t4 * Control.TryParse -> (string -> ^t4 option)) and (Control.TryParse or ^t5) : (static member TryParse : ^t5 * Control.TryParse -> (string -> ^t5 option)) and (Control.TryParse or ^t6) : (static member TryParse : ^t6 * Control.TryParse -> (string -> ^t6 option)) and (Control.TryParse or ^t7) : (static member TryParse : ^t7 * Control.TryParse -> (string -> ^t7 option)) and (Internals.TryParseArray or ^tr) : (static member TryParseArray : ^tr * Internals.TryParseArray -> (string [] -> ^tr option)) // Argument 't' doesn't match
- static member Internals.TryParseArray.TryParseArray : unit * Internals.TryParseArray -> (string [] -> unit) // Argument at index 1 doesn't match Consider adding further type constraintsF# Compiler(71)
很明显，trySscanf有一堆我没有考虑到的过载，我不知道如何做到这一点。
我想做的事情有可能吗？
有趣的是，如果我添加match表达式，编译错误就会消失，但我可能只使用我尝试的第一个匹配情况的PrintfFormat：
let parseLine line =
match line with
| Scan "mem[%i] = %i" (address, value) -> Op address value
| Scan "mask = %s" str -> Mask str
最后一行显示错误：
This expression was expected to have type
'int * int'
but here has type
'string' (F# Compiler(1))
您只是忘记声明函数inline，这样做会很好：
#r "nuget: FSharpPlus"
open FSharpPlus
let inline (|Scan|_|) pattern input = trySscanf pattern input
let res48 =
match "Hello 42 6 World" with
| Scan "Hello %i World" n -> n
| Scan "Hello %i %i World" (n1, n2) -> n1 + n2
之所以要内联声明它，是因为带有约束的函数只能内联声明，这与您想要编写一个为每个数字类型加倍数字输入的函数的情况相同。