search - F# 文档是否可以按类型搜索函数？

Question

假设我想知道 F# 是否有类型的库函数

('T -> bool) -> 'T list -> int

即，计算函数返回 true 的列表中有多少项的东西。 (或返回第一个返回 true 的项目的索引)

在 MSDN 上的文档准备好之前，我曾经在 MSR 站点上使用 F# 的大列表。我可以在页面上搜索上述文本，因为列出了类型。但是现在 MSDN 文档只列出了各个页面上的类型——模块页面是一堆描述性文本。谷歌有点工作，但它无济于事

// compatible interfaces
('T -> bool) -> Seq<'T> -> int
// argument-swaps
Seq<'T> -> ('T -> bool) -> int
// type-variable names
('a -> bool) -> Seq<'a> -> int
// wrappers
('a -> bool) -> 'a list -> option<int>
// uncurried versions
('T -> bool) * 'T list -> int
// .NET generic syntax
('T -> bool) -> List<'T> -> int
// methods
List<'T> member : ('T -> bool) -> int

Haskell 有一个独立的程序，叫做 Hoogle . F# 是否有等价物，例如 Fing 之类的？

Answer 1

我不知道任何这样的工具。然而，使用 System.Reflection 编写一个可能是一个有趣的练习。 (甚至更好的是 PowerPack 中的元数据库)，以便您可以考虑等价模类型变量名称等。

编辑 - 我是对的 - 这是一个有趣的练习。接下来的内容有很多缺点，但对于大约 150 行代码来说还不错。希望这足以让想要使用真正工具的人开始。它没有做任何高级的事情，比如检查带有重新排序参数的函数，而且元数据库对使用完全限定名称有点挑剔，所以你需要小心一点。为了回答您原始帖子中的问题，我执行了

find "('a -> Microsoft.FSharp.Core.bool) -> Microsoft.FSharp.Collections.list`1<'a> -> Microsoft.FSharp.Core.int" 

并得到以下候选人名单:

Microsoft.FSharp.Core.Operators.( + )
Microsoft.FSharp.Core.Operators.( - )
Microsoft.FSharp.Core.Operators.( * )
Microsoft.FSharp.Core.Operators.( / )
Microsoft.FSharp.Core.Operators.( % )
Microsoft.FSharp.Core.Operators.sqrt
Microsoft.FSharp.Core.LanguagePrimitives.EnumOfValue
Microsoft.FSharp.Core.LanguagePrimitives.EnumToValue
Microsoft.FSharp.Core.LanguagePrimitives.AdditionDynamic
Microsoft.FSharp.Core.LanguagePrimitives.CheckedAdditionDynamic
Microsoft.FSharp.Core.LanguagePrimitives.MultiplyDynamic
Microsoft.FSharp.Core.LanguagePrimitives.CheckedMultiplyDynamic
Microsoft.FSharp.Core.LanguagePrimitives.GenericZero
Microsoft.FSharp.Core.LanguagePrimitives.GenericOne
Microsoft.FSharp.Collections.List.find
Microsoft.FSharp.Collections.List.findIndex
Microsoft.FSharp.Collections.List.maxBy
Microsoft.FSharp.Collections.List.minBy

其中，只有 List.findIndex具有您正在寻找的泛型类型，但使用正确的类型参数组合，其他类型参数也是如此(例如，如果 'a = int 则 List.find 具有所需的类型)。不幸的是，搜索中没有考虑约束，因此非 List功能实际上无法匹配。

事不宜迟，这是我使用的代码 - 您需要添加对 FSharp.PowerPack.Metadata 程序集的引用才能使其工作。

open Microsoft.FSharp.Metadata
open System.Text.RegularExpressions

(* type parameters let us switch out representation if need be *)
type Tag<'ty> = | Tuple | Arr | Ground of 'ty
type Ty<'ty,'a> = Param of 'a | Complex of Tag<'ty> * Ty<'ty,'a> list

(* Gets something stable from an FSharpEntity so that we can see if two are identical *)
let rec getType (e:FSharpEntity) =
  if (e.IsAbbreviation) then
    getType e.AbbreviatedType.NamedEntity
  else
    e.ReflectionType

(* FSharpType -> Ty<System.Type,string> *)
let rec cvt (e:FSharpType) =
  if e.IsTuple then
    Complex(Tuple, e.GenericArguments |> Seq.map cvt |> List.ofSeq)
  elif e.IsFunction then
    Complex(Arr, e.GenericArguments |> Seq.map cvt |> List.ofSeq)
  elif e.IsGenericParameter then
    Param e.GenericParameter.Name
  else
    Complex(Ground(e.NamedEntity |> getType), e.GenericArguments |> Seq.map cvt |> List.ofSeq)

(* substitute type for variable within another type *)
let rec subst v t = function
| Complex(tag,l) -> Complex(tag, l |> List.map (subst v t))
| Param i when i = v -> t
| Param j -> Param j

(* get type variables used in a type *)
let rec usedVars = function
| Param i -> Set.singleton i
| Complex(tag, l) -> Set.unionMany (List.map usedVars l)

(* Find most general unifier (if any) for two types *)
let mgu t1 t2 =
  let rec mgu subs = function
  | [] -> Some subs
  | (Complex(tag1,l1),Complex(tag2,l2))::rest ->
       if tag1 <> tag2 then
         None
       else
         let rec loop r = function
         | [],[] -> mgu subs r
         | [],_ | _,[] -> None
         | x::xs, y::ys -> loop ((x,y)::r) (xs,ys)
         loop rest (l1,l2)
  | (Param i, Param j)::rest when i = j -> mgu subs rest
  | ((Param i, x) | (x, Param i))::rest ->
       if (Set.contains i (usedVars x)) then
         None (* type would be infinite when unifying *)
       else
         mgu ((i,x)::subs) (rest |> List.map (fun (t1,t2) -> (subst i x t1, subst i x t2)))
  mgu [] [t1,t2]

(* Active patterns for parsing - this is ugly... *)
let (|StartsWith|_|) r s =
  let m = Regex.Match(s, r)
  if m.Success && m.Index = 0 then
    Some(m.Value, s.Substring(m.Length))
  else None

let rec (|Any|) (|P|_|) = function
| P(x,Any (|P|_|) (l,r)) -> x::l, r
| s -> [],s

let rec (|Any1|_|) (|P|_|) = function
| P(x,Any (|P|_|) (l,r)) -> Some(x::l, r)
| _ -> None

let (|Seq|_|) (|P|_|) (|Q|_|) = function
| P(x,Q(y,r)) -> Some((x,y),r)
| _ -> None

let (|Choice|_|) (|P|_|) (|Q|_|) = function
| P(p) -> Some p
| Q(p) -> Some p
| _ -> None

let (|Delimit|_|) s (|P|_|) = function
| P(x,Any ((|Seq|_|) ((|StartsWith|_|) s) (|P|_|)) (l,r)) -> Some(x::(List.map snd l), r)
| _ -> None

let (|Delimit1|_|) s (|P|_|) = function
| P(x,StartsWith s (_,Delimit s (|P|_|) (l,r))) -> Some(x::l, r)
| _ -> None

(* Basically a BNF grammar for types *)
let rec (|TyE|_|) = function
| ArrE(p) | TupleE(p) | AtomE(p) -> Some(p)
| _ -> None
and (|ArrE|_|) = function
| Choice (|TupleE|_|) (|AtomE|_|) (dom,StartsWith "->" (_,TyE(rng,r))) -> Some(Complex(Arr,[dom;rng]), r)
| _ -> None
and (|TupleE|_|) = function
| Delimit1 @"\*" (|AtomE|_|) (l,r) -> Some(Complex(Tuple,l), r)
| _ -> None
and (|AtomE|_|) = function
| ParamE(x,r) | GroundE(x,r) | StartsWith @"\(" (_,TyE(x,StartsWith @"\)" (_,r))) -> Some(x,r)
| _ -> None
and (|ParamE|_|) = function
| StartsWith "'[a-zA-Z0-9]+" (s,r) -> Some(Param s, r)
| _ -> None
and (|GroundE|_|) = function
| StartsWith "[`.a-zA-Z0-9]+" (gnd, StartsWith "<" (_, Delimit "," (|TyE|_|) (l, StartsWith ">" (_,r)))) -> 
      let ty = FSharpAssembly.FSharpLibrary.GetEntity gnd |> getType
      Some(Complex(Ground(ty), l), r)
| StartsWith "[`.a-zA-Z0-9]+" (gnd, r) ->
      let ty = FSharpAssembly.FSharpLibrary.GetEntity gnd |> getType
      Some(Complex(Ground(ty), []), r)
| _ -> None

(* parse a string into a type *)
let parse (s:string) =
  (* remove whitespace before matching *)
  match s.Replace(" ","") with
  | TyE(ty,"") -> ty
  | _ -> failwith "Not a well-formed type"

(* an infinite stream of possible variable names - for performing renaming *)
let rec names = 
  let letters = ['a' .. 'z'] |> List.map string
  seq {
    yield! letters
    for n in names do
      for l in letters do
        yield n + l
  }

(* finds entities in the F# library with the requested signature, modulo type parameter unification *)
let find s =
  let ty = parse s
  let vars = usedVars ty
  seq {
    for e in FSharpAssembly.FSharpLibrary.Entities do
    for m in e.MembersOrValues do
      (* need try/catch to avoid error on weird types like "[]`1" *)
      match (try Some(cvt m.Type) with _ -> None) with
      | Some ty2 ->
        (* rename all type variables from the query to avoid incorrectly unifying with type variables in signatures *)
        let used = usedVars ty2
        let newVars = Seq.choose (fun v -> if Set.contains v used then None else Some(Param v)) names
        let varMap = Map.ofSeq (Seq.zip vars newVars)
        let ty = Map.fold (fun t v p -> subst v p t) ty varMap
        match mgu ty ty2 with
        | None -> ()
        | Some _ -> yield sprintf "%s.%s.%s" e.Namespace e.DisplayName m.DisplayName 
      | _ -> () }