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How to use correctly try - with?
f#

I will get access violation exceptions when running allFiles examples (p.58 and p.61 Expert F#). That's OK, should be. Now I try to modify these examples so, they just ignore the access violation exceptions and proceed. I was success with example in page 58, but not with example in page 61. Where I'm wrong?

//example from page 58

open System.IO

#nowarn "67"

let rec allFiles dir =

try

Seq.append

(dir |> Directory.GetFiles)

(dir |> Directory.GetDirectories |> Seq.map allFiles |> Seq.concat )

with :? System.Exception as e -> Seq.empty

allFiles @"c:\WINDOWS\system32" |> Seq.iter (fun s -> printfn "%A" s)

//modified example from page 61

#nowarn "57"

#nowarn "67"

let rec allFiles1 dir =

try

seq { for file in Directory.GetFiles(dir) -> file

for subdir in Directory.GetDirectories dir ->> (allFiles1 subdir) }

with :? System.Exception as e -> Seq.empty

allFiles1 @"c:\WINDOWS\system32" |> Seq.iter (fun s -> printfn "%A" s)

.

You just forgot the do's. By the way, the compiler recommends you use yield and yield! instead of -> and ->>. Also, all exceptions will hold when upcasting to System.Exception, so you don't have to bind it to 'e'.

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let rec allFiles1 dir =
    try
        seq { for file in Directory.GetFiles(dir) do
                yield file
              for subdir in Directory.GetDirectories dir do
                yield! (allFiles1 subdir) }
    with _ -> Seq.empty

EDIT: Something was bothering me, so I retried the code you entered. I was able to get it to run with no modifications. So, I would assume that there is a problem with your spacing. Try copying/pasting the following code into your file and see if that works:

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let rec allFiles1 dir =
  try
    seq { for file in Directory.GetFiles(dir) -> file
          for subdir in Directory.GetDirectories dir ->> (allFiles1 subdir) }
  with :? System.Exception as e -> Seq.empty

allFiles1 @"c:\WINDOWS\system32" |> Seq.iter (fun s -> printfn "%A" s)

Regards,

z.

By on 1/26/2008 12:45 PM ()

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