Converting seq<string> to string[] in F#

问题

The example from this post has an example

open System.IO

let lines = 
  File.ReadAllLines("tclscript.do")
  |> Seq.map (fun line ->
      let newLine = line.Replace("{", "{{").Replace("}", "}}")
      newLine )

File.WriteAllLines("tclscript.txt", lines)

that gives an error when compilation.

error FS0001: This expression was expected to have type
    string []    
but here has type
    seq<string> 

How to convert seq to string[] to remove this error message?

回答1:

Building on Jaime's answer, since ReadAllLines() returns an array, just use Array.map instead of Seq.map

open System.IO

let lines = 
  File.ReadAllLines("tclscript.do")
  |> Array.map (fun line ->
      let newLine = line.Replace("{", "{{").Replace("}", "}}")
      newLine )

File.WriteAllLines("tclscript.txt", lines)

回答2:

You can use

File.WriteAllLines("tclscript.txt", Seq.toArray lines)

or alternatively just attach

|> Seq.toArray

after the Seq.map call.

(Also note that in .NET 4, there is an overload of WriteAllLines that does take a Seq)

回答3:

Personally, I prefer sequence expressions over higher-order functions, unless you're piping the output through a series of functions. It's usually cleaner and more readable.

let lines = [| for line in File.ReadAllLines("tclscript.do") -> line.Replace("{", "{{").Replace("}", "}}") |]
File.WriteAllLines("tclscript.txt", lines)

With regex replacement

let lines = 
  let re = System.Text.RegularExpressions.Regex(@"#(\d+)")
  [|for line in File.ReadAllLines("tclscript.do") ->
      re.Replace(line.Replace("{", "{{").Replace("}", "}}"), "$1", 1)|]
File.WriteAllLines("tclscript.txt", lines)

来源：https://stackoverflow.com/questions/6156358/converting-seqstring-to-string-in-f