Crash reading a file

Crash reading a file

[tmp123]

Hello,

The following program (foo.ml):

value rec read_stdin () =
  try
    [ (input_line Pervasives.stdin) :: (read_stdin ()) ]
  with [ End_of_file -> [] ];

value main () =
  read_stdin();

main();


when compiled with "ocamlopt -pp camlp4r foo.ml" and executed "./a.out", 
produces a segmentation fault, but I'm not able to find why.

Please, has someone any sugestion?

Thanks a lot.

Re: [Caml-list] Crash reading a file

[Adam Chlipala]

Your function isn't tail recursive, so it uses stack space proportional 
to the number of lines in the file.  "Segmentation fault" may be your 
architecture's "stack overflow" error.

tmp123 wrote:
> The following program (foo.ml):
>
> value rec read_stdin () =
>  try
>    [ (input_line Pervasives.stdin) :: (read_stdin ()) ]
>  with [ End_of_file -> [] ];
>
> value main () =
>  read_stdin();
>
> main();
>
>
> when compiled with "ocamlopt -pp camlp4r foo.ml" and executed 
> "./a.out", produces a segmentation fault, but I'm not able to find why.
>
> Please, has someone any sugestion? 

Re: [Caml-list] Crash reading a file

[Chet Murthy]

Besides Adam's correct obervation that you're recursing in a non-tail
manner, note also that Ocaml doesn't guarantee any specific
order-of-evaluation, wihch means that the recursive call in the cons
-could- be evaluated before the input_line.  In fact, since the
-current- implementation -does- evaluate in right-to-left order, that
-is- what's going to happen.

# let f x = Printf.fprintf stderr "%s\n" x; flush stderr; x;;
val f : string -> string = <fun>
# let l = ((f"a")::(f"b")::[]);;
b
a
val l : string list = ["a"; "b"]

My guess is, you're getting infinite stack-recursion for even empty
files.  Make your order of evaluation explicit, and you'll only get it
for large files.

--chet--

On Monday 04 February 2008 06:54, tmp123 wrote:
> Hello,
>
> The following program (foo.ml):
>
> value rec read_stdin () =
>   try
>     [ (input_line Pervasives.stdin) :: (read_stdin ()) ]
>   with [ End_of_file -> [] ];
>
> value main () =
>   read_stdin();
>
> main();
>
>
> when compiled with "ocamlopt -pp camlp4r foo.ml" and executed "./a.out",
> produces a segmentation fault, but I'm not able to find why.
>
> Please, has someone any sugestion?
>
> Thanks a lot.
>
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Re: [Caml-list] Crash reading a file

[tmp123]

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Re: [Caml-list] Crash reading a file

[Ashish Agarwal]

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> but then I must append at the end of a list, that is something time
consuming. I do not known about more options.

Append to the beginning of the list during the recursion, producing the list
in reverse. Then do a List.rev at the end.

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Re: [Caml-list] Crash reading a file

[Loup Vaillant]

2008/2/4, Ashish Agarwal <agarwal1975@gmail.com>:
> > but then I must append at the end of a list, that is something time
> consuming. I do not known about more options.
>
> Append to the beginning of the list during the recursion, producing the list
> in reverse. Then do a List.rev at the end.

If you don't need persistence, you can also use a stream. That way,
the stream will be consumed only as needed, and you'll have a constant
space usage, (both heap and stack).