[Caml-list] Better option to read a file

[Caml-list] Better option to read a file

[Agustín Valverde]

Hi

In a program  I need to read the input data from a file and I have 
written several options. I want to obtain the string of characters from 
a text file and I don't know what is the better option. Among others, I 
have written the following:

First option:

let leer_file fl =
      let form = ref "" in
      let arch = open_in fl in
      let long = in_channel_length arch in
      form := String.create (long-1);
      really_input arch (!form) 0 (long-1);
      close_in arch;
      !form;;

Second:

let rec unir c ac = unir ac^(Char.escaped c);;

let leer2 fl =
      let form = ref "" in
      let c = ref '-' in
      let arch = open_in fl in
      (try
        (while true do (c := input_char arch); (if !c != '\n' then (form 
:= unir !c !form) else ()) done)
      with End_of_file -> close_in arch);
      !form;;

I also have a parser to convert the string, could I to improve these 
functions merging them with the parser in some way?

Thanks for your help

Agustín Valverde
Department of Applied Mathematics
University of Malaga, Spain

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Re: [Caml-list] Better option to read a file

[Pietro Abate]

what's about ....

let file_ch = (open_in input_file) in
let read_lines =
    let read_new_line n =
        try Some (input_line file_ch)
        with End_of_file -> None
    in
        Stream.from read_new_line
in
let rec get_line () = 
    match Stream.next read_lines with
    |s when Str.string_match (Str.regexp "^[\n\t ]+$") s 0 -> get_line ()
    |s -> s
in

p

On Tue, Mar 16, 2004 at 10:28:37PM +0100, Agust?n Valverde wrote:
> Hi
> 
> In a program  I need to read the input data from a file and I have 
> written several options. I want to obtain the string of characters from 
> a text file and I don't know what is the better option. Among others, I 
> have written the following:
> 
> First option:
> 
> let leer_file fl =
>      let form = ref "" in
>      let arch = open_in fl in
>      let long = in_channel_length arch in
>      form := String.create (long-1);
>      really_input arch (!form) 0 (long-1);
>      close_in arch;
>      !form;;
> 
> Second:
> 
> let rec unir c ac = unir ac^(Char.escaped c);;
> 
> let leer2 fl =
>      let form = ref "" in
>      let c = ref '-' in
>      let arch = open_in fl in
>      (try
>        (while true do (c := input_char arch); (if !c != '\n' then (form 
> := unir !c !form) else ()) done)
>      with End_of_file -> close_in arch);
>      !form;;
> 
> I also have a parser to convert the string, could I to improve these 
> functions merging them with the parser in some way?
> 
> Thanks for your help
> 
> Agust?n Valverde
> Department of Applied Mathematics
> University of Malaga, Spain
> 
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Re: [Caml-list] Better option to read a file

[Christoph Bauer]

Hi Agustín,

I'm not quite sure, what you want.  `leer' reads a whole file (this
whitout a upper limit on `long' a bad idea), `unir' doesn't work and
`leer2' is `read the first line of file and don't close the file'.
(Do you mean `let leer2 = input_line'?)

Because of `leer2', I assume you have a parser operating on lines.  As
Pietro I suggest the use of streams. A slightly more general approach
could improve the reuse of your code.


A file is a stream of chars but mostly you want to access whole lines
or words. Therefore we write this three functions:


let splitted_stream ~on_words char_stream = 
  let buf = Buffer.create 256 in
  let this_string () = 
    let str = Buffer.contents buf in
      Buffer.reset buf; str in
  let rec accumulate =
    parser 
	[< ''\n'; rest >] -> [< '(this_string ()); remove_cr rest >]
      | [< '' ' | '\t' as c; rest >] -> 
	  if on_words then [< '(this_string ()); accumulate rest >] 
	  else (
	    Buffer.add_char buf c;
	    accumulate rest
	  )
      | [< 'c; rest >] ->
	  Buffer.add_char buf c;
	  accumulate rest
      | [< >] -> [< >]
  and remove_cr = 
    parser 
	[< ''\r'; rest >] -> accumulate rest
      | [< rest >] -> accumulate rest
  in accumulate char_stream


let line_stream = splitted_stream ~on_words:false
let word_stream = splitted_stream ~on_words:true


Please note, that the input Stream could be obtained by Stream.of_channel,
Stream.of_string or Stream.from. The next function should apply your parser.

let rec stream_map f =
  parser
      [< 'a; rest >] -> [< '(f a); iter f rest >]
    | [< >] -> [< >]


The functions so far should be put in a generic library.

Assummed your parser is a function

parse_line: string -> 'a

then you can get the desired 'a Stream with

  let astream = stream_map parse_line (line_stream (Stream.of_channel (open_in fl)))

Regards,
Christoph Bauer




> Hi
>
> In a program  I need to read the input data from a file and I have
> written several options. I want to obtain the string of characters
> from a text file and I don't know what is the better option. Among
> others, I have written the following:
>
> First option:
>
> let leer_file fl =
>       let form = ref "" in
>       let arch = open_in fl in
>       let long = in_channel_length arch in
>       form := String.create (long-1);
>       really_input arch (!form) 0 (long-1);
>       close_in arch;
>       !form;;
>
> Second:
>
> let rec unir c ac = unir ac^(Char.escaped c);;
>
> let leer2 fl =
>       let form = ref "" in
>       let c = ref '-' in
>       let arch = open_in fl in
>       (try
>         (while true do (c := input_char arch); (if !c != '\n' then
> (form := unir !c !form) else ()) done)
>       with End_of_file -> close_in arch);
>       !form;;
>
> I also have a parser to convert the string, could I to improve these
> functions merging them with the parser in some way?
>
> Thanks for your help
>
> Agustín Valverde
> Department of Applied Mathematics
> University of Malaga, Spain
>
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
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Re: [Caml-list] Better option to read a file

[Jean-Christophe Filliatre]

Agustín Valverde writes:

 > Second:
 > 
 > let rec unir c ac = unir ac^(Char.escaped c);;
 > 
 > let leer2 fl =
 >       let form = ref "" in
 >       let c = ref '-' in
 >       let arch = open_in fl in
 >       (try
 >         (while true do (c := input_char arch); (if !c != '\n' then (form 
 > := unir !c !form) else ()) done)
 >       with End_of_file -> close_in arch);
 >       !form;;

Note that this function is very inefficient: you are indeed building a
lot  of intermediate  strings with  "unir", resulting  in  a quadratic
space (even if the final string occupies linear space).

Using a buffer as suggested by Christoph is clearly better (the module
Buffer  from ocaml standard  library is  doubling its  internal string
buffer as needed, without you to worry about it).

 > I also have a parser to convert the string, could I to improve these 
 > functions merging them with the parser in some way?

The use  of ocamllex  in combination  with a buffer  is both  easy and
efficient. I sketch it:

======================================================================
{ 
  open Lexing 
  let buf = Buffer.create 1024
}

rule read = parse
  | "\\n"  { Buffer.add_char buf '\n'; read lexbuf }
  | "\\t"  { Buffer.add_char buf '\t'; read lexbuf }
  | "\\\\" { Buffer.add_char buf '\\'; read lexbuf }
  | _      { Buffer.add_string buf (lexeme lexbuf); read lexbuf }
  | eof    { Buffer.contents buf }

{
  let read_file f =
    let cin = open_in f in
    let lb = from_channel cin in
    let s = read lb in
    close_in cin;
    s
}
======================================================================

-- 
Jean-Christophe Filliâtre (http://www.lri.fr/~filliatr)

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Re: [Caml-list] Better option to read a file

[Markus Mottl]

Hi,

I usually use one of the two functions below to read in whole strings.
Function "read_file" does the obvious: read a file as fast as possible
into a string.

Function "read_channel" reads a channel of unbounded size (as long as the
maximum string length is not exceeded, of course).  It also takes the
optional argument "buf_size", which you can set depending on the kind
of channel you read from (the default 4096 bytes are somewhat optimal
when reading from files on Linux).

---------------------------------------------------------------------------
let rec copy_lst res ofs = function
  | [] -> res
  | (str, len) :: t ->
      let pos = ofs - len in
      String.unsafe_blit str 0 res pos len;
      copy_lst res pos t

let read_channel ?(buf_size = 4096) =
  let rec loop len lst ch =
    let buf = String.create buf_size in
    let n = input ch buf 0 buf_size in
    if n <> 0 then loop (len + n) ((buf, n) :: lst) ch
    else copy_lst (String.create len) len lst in
  loop 0 []

let read_file name =
  let file = open_in name in
  let size = in_channel_length file in
  try
    let buf = String.create size in
    really_input file buf 0 size;
    close_in file;
    buf
  with exc ->
    (try close_in file with _ -> ());
    raise exc
---------------------------------------------------------------------------

Regards,
Markus Mottl

-- 
Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at

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Re: [Caml-list] Better option to read a file

[Agustin Valverde Ramos]

El 17/03/2004, a las 8:31, Christoph Bauer escribió:

> I'm not quite sure, what you want.  `leer' reads a whole file (this
> whitout a upper limit on `long' a bad idea),

The unlimited long is the unique problem or is there another drawbacks?

>  `unir' doesn't work and

Yes, I wrote bad the definition in the email (let rec unir c ac = 
ac^(Char.escaped c);;), but I have understood that, any case, this is a 
bad idea.

> `leer2' is `read the first line of file and don't close the file'.
> (Do you mean `let leer2 = input_line'?)
>
> Because of `leer2', I assume you have a parser operating on lines.

No, my parser works over all the file content. I want to read formulas 
like the following:

((p | (r -> t)) &
(q | (t -> s)))
-> ((p & -(q -> -t)) |
(r -> ((q -> (s | r)) & s)))

For example, I have a file of 752Kb with 770028 characters and I forget 
the newline char to reduce the size of the resulting string. So I don't 
know if I can apply the Chirstoph and Pietro ideas directly.

I think that the Markus suggestion is better for me, because I have 
never worked with ocamllex. By the way, can I obtain benefits in 
efficiency using ocamllex? because in this case I'll learn to use it.

Thanks for all answers

*******************************
*  Agustín Valverde Ramos
*  Dept. Matemática Aplicada
*  E.T.S. de Ingeniería Informática
*  Universidad de Málaga
*  Campus de Teatinos
*  29071 Málaga (España)
*  ---------------------------------
*  Tel:  (+34)  952132878
*  Fax: (+34)  952132746
*  mailto:a_valverde@ctima.uma.es
*  http://www.AgustinValverde.com
*  ---------------------------------
*  Soy miembro de GIMAC:
*  "Grupo de Investigación
*  en Matemática Aplicada para la Computación"
*  http://batllo.informatica.uma.es/aciego/gimac-home.html
*
*  I am member of GIMAC:
*  "Research Group in Applied Mathematics for
*  Computer Science"
*  http://batllo.informatica.uma.es/aciego/gimac-home-eng.html
*******************************

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Re: [Caml-list] Better option to read a file

[Markus Mottl]

On Wed, 17 Mar 2004, Agustin Valverde Ramos wrote:
> No, my parser works over all the file content. I want to read formulas 
> like the following:
[snip]
> I think that the Markus suggestion is better for me, because I have 
> never worked with ocamllex. By the way, can I obtain benefits in 
> efficiency using ocamllex? because in this case I'll learn to use it.

Please do yourself a favor, save a lot of work and use ocamllex and
ocamlyacc.  These tools are the Right Thing (tm) for the job.  Since I had
a very similar project handy, here are the files you need to get going:

file: ast.ml
Contains abstract syntax tree and pretty printer for logical expressions
---------------------------------------------------------------------------
open Format

type expr =
  | Id of string
  | Not of expr
  | And of expr * expr
  | Or of expr * expr
  | Imp of expr * expr

let rec pp_expr ppf = function
  | Id id -> pp_print_string ppf id
  | Not e -> fprintf ppf "-%a" pp_expr e
  | And (e1, e2) -> fprintf ppf "(@[%a &@ %a@])" pp_expr e1 pp_expr e2
  | Or (e1, e2) -> fprintf ppf "(@[%a |@ %a@])" pp_expr e1 pp_expr e2
  | Imp (e1, e2) -> fprintf ppf "(@[%a ->@ %a@])" pp_expr e1 pp_expr e2
---------------------------------------------------------------------------

file: parser.mly
Contains the translator: tokens -> abstract syntax tree
---------------------------------------------------------------------------
%token <string> ID
%token NOT AND OR IMP LPAREN RPAREN EOF

%start main
%type <Ast.expr> main

%%

main : expr EOF { $1 }

expr
  : ID { Ast.Id $1 }
  | LPAREN expr bin_op expr RPAREN { $3 $2 $4 }
  | NOT expr { Ast.Not $2 }

bin_op
  : AND { fun arg1 arg2 -> Ast.And (arg1, arg2) }
  | OR  { fun arg1 arg2 -> Ast.Or (arg1, arg2) }
  | IMP { fun arg1 arg2 -> Ast.Imp (arg1, arg2) }
---------------------------------------------------------------------------

file: lexer.mll
Contains the translator: string -> tokens
---------------------------------------------------------------------------
{ open Parser }

rule token = parse
  | [' ' '\t' '\n']     { token lexbuf }
  | ['a' - 'z']+ as id  { ID id }
  | '&'                 { AND }
  | '|'                 { OR }
  | "->"                { IMP }
  | "-"                 { NOT }
  | '('                 { LPAREN }
  | ')'                 { RPAREN }
  | eof                 { EOF }

{
  let lexbuf = Lexing.from_channel stdin in
  let ast = Parser.main token lexbuf in
  Format.printf "%a@." Ast.pp_expr ast
}
---------------------------------------------------------------------------

file: Makefile
Requires OCamlMakefile
---------------------------------------------------------------------------
SOURCES = ast.ml parser.mly lexer.mll
RESULT  = parse

include OCamlMakefile
---------------------------------------------------------------------------

Just type "make" and the resulting "parse"-program will read in your
logical expressions from stdin until EOF and pretty-print them (note:
the topmost expression also needs parenthesis!). E.g.:

file: test.dat
---------------------------------------------------------------------------
(
  (
    (p | (r -> t)) &
    (q | (t -> s))
  ) ->
  (
    (p & -(q -> -t)) |
    (r -> ((q -> (s | r)) & s))
  )
)
---------------------------------------------------------------------------

Running "parse < test.dat" should yield:

(((p | (r -> t)) & (q | (t -> s))) ->
 ((p & -(q -> -t)) | (r -> ((q -> (s | r)) & s))))

Have fun!

Regards,
Markus

-- 
Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at

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Re: [Caml-list] Better option to read a file

[Agustin Valverde Ramos]

A lot of thanks, Markus. In fact, I'm reading and studying about 
ocamllex/yacc and this code will help me. Just a couple of questions.

> type expr =
>   | Id of string
>   | Not of expr
>   | And of expr * expr
>   | Or of expr * expr

I want to work with conjunctions and disjunctions of lists:

      | And of expr list
      | Or of expr list

Is it hard/possible to modify  the rest of the code?

>  (note: the topmost expression also needs parenthesis!). E.g.:

Why? is it possible to release this restriction?

*******************************
*  Agustín Valverde Ramos
*  Dept. Matemática Aplicada
*  E.T.S. de Ingeniería Informática
*  Universidad de Málaga
*  Campus de Teatinos
*  29071 Málaga (España)
*  ---------------------------------
*  Tel:  (+34)  952132878
*  Fax: (+34)  952132746
*  mailto:a_valverde@ctima.uma.es
*  http://www.AgustinValverde.com
*  ---------------------------------
*  Soy miembro de GIMAC:
*  "Grupo de Investigación
*  en Matemática Aplicada para la Computación"
*  http://batllo.informatica.uma.es/aciego/gimac-home.html
*
*  I am member of GIMAC:
*  "Research Group in Applied Mathematics for
*  Computer Science"
*  http://batllo.informatica.uma.es/aciego/gimac-home-eng.html
*******************************

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Re: [Caml-list] Better option to read a file

[Markus Mottl]

On Wed, 17 Mar 2004, Agustin Valverde Ramos wrote:
> I want to work with conjunctions and disjunctions of lists:
> 
>      | And of expr list
>      | Or of expr list
> 
> Is it hard/possible to modify  the rest of the code?

I suppose you prefer this representation, because you want to stratify
logical expressions.  The the other representation is otherwise easier
to handle.  It's possible and not too hard to make this extension (a
bit tedious though).

> > (note: the topmost expression also needs parenthesis!). E.g.:
> 
> Why? is it possible to release this restriction?

It's simpler this way.  You just need to add the parenthesis-free
expressions to the "main" nonterminal if you don't want this.

Regards,
Markus

-- 
Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at

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[Caml-list] Better option to read a file

[Agustín Valverde]

Hi

In a program  I need to read the input data from a file and I have 
written several options. I want to obtain the string of characters from 
a text file and I don't know what is the better option. Among others, I 
have written the following:

First option:

let leer_file fl =
      let form = ref "" in
      let arch = open_in fl in
      let long = in_channel_length arch in
      form := String.create (long-1);
      really_input arch (!form) 0 (long-1);
      close_in arch;
      !form;;

Second:

let rec unir c ac = unir ac^(Char.escaped c);;

let leer2 fl =
      let form = ref "" in
      let c = ref '-' in
      let arch = open_in fl in
      (try
        (while true do (c := input_char arch); (if !c != '\n' then (form 
:= unir !c !form) else ()) done)
      with End_of_file -> close_in arch);
      !form;;

I also have a parser to convert the string, could I to improve these 
functions merging them with the parser in some way?

Thanks for your help

Agustín Valverde
Department of Applied Mathematics
University of Malaga, Spain
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