将 OCaml 代码转换为 F#

Question

我正在将一些 OCaml 代码转换为 F#，但 OCaml let...and... 存在问题，该问题仅存在于 F# 中，使用递归函数。 我有给定的 OCaml 代码：

let matches s = let chars = explode s in fun c -> mem c chars
let space = matches " \t\n\r"
and punctuiation = matches "() [] {},"
and symbolic = matches "~'!@#$%^&*-+=|\\:;<>.?/"
and numeric = matches "0123456789"
and alphanumeric = matches "abcdefghijklmopqrstuvwxyz_'ABCDEFGHIJKLMNOPQRSTUVWXYZ"

我想在这两种方法中使用：

let rec lexwhile prop inp = match inp with
c::cs when prop c -> let tok,rest = lexwhile prop cs in c+tok,rest
|_->"",inp

let rec lex inp = 
match snd(lexwhile space inp)with
[]->[]
|c::cs ->let prop = if alphanumeric(c) then alphanumeric
                    else if symbolic(c) then symbolic
                    else fun c ->false in
                    let toktl,rest = lexwhile prop cs in
                    (c+toktl)::lex rest

有人知道我必须如何更改它以便我可以使用它吗？

Answer 1

您似乎正在尝试翻译“Handbook of Practical Logic and Automated Reasoning”。

您看到了吗：An F# version of the book code 现已推出！感谢 Eric Taucher、Jack Pappas 和 Anh-Dung Phan。

你需要看intro.fs

// pg. 17 
// ------------------------------------------------------------------------- // 
// Lexical analysis.                                                         // 
// ------------------------------------------------------------------------- // 


let matches s =  
    let chars =  
        explode s  
    fun c -> mem c chars 

let space = matches " \t\n\r"  

let punctuation = matches "()[]{}," 

let symbolic = matches "~`!@#$%^&*-+=|\\:;<>.?/" 

let numeric = matches "0123456789" 

let alphanumeric = matches "abcdefghijklmnopqrstuvwxyz_'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" 

let rec lexwhile prop inp = 
    match inp with 
    | c :: cs when prop c -> 
        let tok, rest = lexwhile prop cs 
        c + tok, rest 
    | _ -> "", inp 

let rec lex inp = 
    match snd <| lexwhile space inp with 
    | [] -> [] 
    | c :: cs -> 
        let prop = 
            if alphanumeric c then alphanumeric 
            else if symbolic c then symbolic 
            else fun c -> false 
        let toktl, rest = lexwhile prop cs 
        (c + toktl) :: lex rest

我在翻译时问了很多questions，并在他们前面加上Converting OCaml to F#:。如果您查看 cmets，您会看到我们三个人是如何参与这个项目的。

Answer 2

你可以写：

let explode s = [for c in s -> string c]
let matches str strc = 
    let eStr = explode str
    List.contains strc eStr 
let space = matches " \t\n\r"
let punctuation = matches "() [] {},"
let symbolic = matches "~'!@#$%^&*-+=|\\:;<>.?/"
let numeric = matches "0123456789"
let alphanumeric = matches "abcdefghijklmopqrstuvwxyz_'ABCDEFGHIJKLMNOPQRSTUVWXYZ"

F# 倾向于使用轻量级而非冗长的语法编写，因此您通常不需要使用in、begin 和end 关键字。有关差异的详细信息，请参阅：https://msdn.microsoft.com/en-us/library/dd233199.aspx。

就个人而言，我可能会将所有这些 string -> bool 函数重构为活动模式，例如：

let (|Alphanumeric|_|) str =
    match matches "abcdefghijklmopqrstuvwxyz_'ABCDEFGHIJKLMNOPQRSTUVWXYZ" str with
    |true -> Some str
    |false -> None

let (|Symbolic|_|) str =
    match matches "~'!@#$%^&*-+=|\\:;<>.?/" str with
    |true -> Some str
    |false -> None

然后你可以进行模式匹配，例如：

match c with
|Alphanumeric _ -> // alphanumeric case
|Symbolic _ -> // symbolic case
|_ -> // other cases