F# 函数调用ain'；t工作不正常

我在F#中遇到了代码和平的问题，我写道。 我在F#中制作了一个堆栈结构，还制作了push和pop函数，所有这些看起来都很好。 我还制作了一些指令（ADD、MULT、PUSH、ABS），用于处理堆栈中的整数项。 我做了一个函数，作为指令的中间计；它在输入端得到一个堆栈和一条指令，输出端是包含指令结果的堆栈。当我尝试在解释器中使用push函数时，它不再工作，它完全忽略了命令

type stack = 
 | Stck of int list

type instr =
 | ADD
 | MULT
 | PUSH of int
 | ABS

let stackPush stck num = 
match stck with
    | Stck(someList) ->
        match someList with
            | [] -> Stck[num]
            | _ -> Stck(num::someList)

let stackPop stck =
match stck with
    | Stck(someList) -> 
        match someList with
            | [] -> Stck[]
            | _::xEnd -> Stck(xEnd)

let getFirstItem stck = 
match stck with  
    | Stck(someList) -> 
        match someList with
            | [] -> 0
            | [xOnly] -> xOnly
            | xStart::_ -> xStart

let exec stck instr =
match stck with 
    | Stck(someList) -> 
        match someList with
            | [] -> Stck[]
            | [xOnly] -> Stck[xOnly] 
            | xStart::xMid::xEnd ->
                let tempStack = stackPop(stackPop(stck))
                match instr with  
                    | ADD ->                        
                        match tempStack with
                            | _ -> Stck((xStart + xMid)::xEnd)                           
                    | MULT ->
                        match tempStack with
                            | _ -> Stck((xStart * xMid)::xEnd)                            
                    | PUSH x -> stackPush stck x
                    | ABS -> Stck(abs( xStart)::xEnd)

当我运行它们时，问题就出现了

let mutable stackProva = Stck[]
stackProva <- exec stackProva (PUSH 5) //not working

let可变stackProva=Stck[]
stackProva问题在于
exec
的实现。如果它使用空堆栈，它会立即返回空堆栈

以下是工作版本：

type Stack = Stack of int list

type Instruction =
    | ADD
    | MULT
    | ABS
    | PUSH of int

let push num (Stack stack) = Stack (num::stack)

let pop (Stack stack) =
    match stack with
    | [] -> []
    | _::tail -> tail

let tryGetFirstItem (Stack stack) = List.tryHead stack

let exec instr (Stack stack) =
    match stack, instr with
    | s1::s2::tail, ADD    -> Stack (s1+s2::tail)
    | s1::s2::tail, MULT   -> Stack (s1*s2::tail)
    | s1::tail,     ABS    -> Stack (abs(s1)::tail)
    | _,            PUSH x -> push x (Stack stack)        
    | x,            _      -> Stack x

Stack []
|> exec (PUSH 1)
|> exec (PUSH 2)
|> exec ADD
|> tryGetFirstItem
|> printfn "%A" //prints "Some 3"

type Stack = Stack of int list

type Instruction =
    | ADD
    | MULT
    | ABS
    | PUSH of int

let push num (Stack stack) = Stack (num::stack)

let pop (Stack stack) =
    match stack with
    | [] -> []
    | _::tail -> tail

let tryGetFirstItem (Stack stack) = List.tryHead stack

let exec instr (Stack stack) =
    match stack, instr with
    | s1::s2::tail, ADD    -> Stack (s1+s2::tail)
    | s1::s2::tail, MULT   -> Stack (s1*s2::tail)
    | s1::tail,     ABS    -> Stack (abs(s1)::tail)
    | _,            PUSH x -> push x (Stack stack)        
    | x,            _      -> Stack x

Stack []
|> exec (PUSH 1)
|> exec (PUSH 2)
|> exec ADD
|> tryGetFirstItem
|> printfn "%A" //prints "Some 3"