我有这个代码：
let main argv =
let x="b"
match x with
| _ when Regex.Match(x,"a").Success=true->
let a=Regex.Match(x,"a")
Console.WriteLine(a.Groups.[0])
| _ when Regex.Match(x,"b").Success=true->
let b=Regex.Match(x,"b")
Console.WriteLine(b.Groups.[0])
我必须在上面的代码中两次写Regex.Match(x,“a”)和Regex.Match(x,“b”).有没有办法只写一次？
解决方法
寻找活跃的模式：
let (|Match|_|) pattern input =
let m = Regex.Match(input,pattern,RegexOptions.Singleline)
if m.Success
then Some (m.Groups.[0])
else None
// and use it:
match x with
| Match @"a text" a ->
printfn "found a: %s" a
| Match @"b text" b ->
printfn "found b: %s" b
您可以更进一步,创建一个支持其自身解析值的活动模式：
let (|Regex|_|) pattern input =
let m = Regex.Match(input,RegexOptions.Singleline)
if m.Success
// List.tail is needed to skip the m.Groups.[0] that returns the entire parsed scope
then [ for g in m.Groups -> g.Value ] |> List.tail |> Some
else None
match x with
| Regex @"a (\w+)\s(\w+)" [ a1; a2 ] ->
printfn "found A value: %s and %s" a1 a2
| Regex @"b (\w+)\s(\w+)\s(\w+)" [ b1; b2; b3 ] ->
printfn "found B value: %s and %s and %s" b1 b2 b3
// this will be able to parse the following:
// "a foo bar" ==> a1="foo" and a2="bar"
// "b foo bar baz" ==> b1="foo",b2="bar",and b3="baz"
