Pervasives or Printf module ?

Pervasives or Printf module ?

[sejourne_kevin]

Hi list,

As the usage of:
           Printf.sprintf "_%d" x
and
           "_"^(string_of_int x)
is the same,
what is the
better solution?

Do you have an opinion for the one or the second?


Kévin.

	

	
		
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Re: [Caml-list] Pervasives or Printf module ?

[Jon Harrop]

On Sunday 22 January 2006 15:10, sejourne_kevin wrote:
> As the usage of:
>            Printf.sprintf "_%d" x
> and
>            "_"^(string_of_int x)

That can be written without parentheses and the style guide advises the use of 
spaces around operators (i.e. "^"):

  "_" ^ string_of_int x

> is the same, what is the better solution?
>
> Do you have an opinion for the one or the second?

I tend to avoid Printf and stick with Pervasives where possible.

You can do some nice things with printf, like exploit currying:

# List.iter (Printf.printf "%d ") [1;2;3];;
1 2 3 - : unit = ()

but it is easy to trip up:

# List.iter (Printf.printf " %d") [1;2;3];;
 123- : unit = ()

Note: the former prints a space after every integer whereas the latter prints 
only a single space at the beginning. To get the latter to act as the former 
does, you must beta expand (I think that is the correct technical term) to 
postpone the computation of printf " ":

# List.iter (fun n -> Printf.printf " %d" n) [1;2;3];;
 1 2 3- : unit = ()

If efficiency is a concern then I would expect printf to be faster because it 
should avoid string concatenation. I haven't tested that though...

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
Objective CAML for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists

Re: [Caml-list] Pervasives or Printf module ?

[Anil Madhavapeddy]

On Sun, Jan 22, 2006 at 03:34:04PM +0000, Jon Harrop wrote:
> 
> You can do some nice things with printf, like exploit currying:
> 
> # List.iter (Printf.printf "%d ") [1;2;3];;
> 1 2 3 - : unit = ()
> 
> but it is easy to trip up:
> 
> # List.iter (Printf.printf " %d") [1;2;3];;
>  123- : unit = ()
> 
> Note: the former prints a space after every integer whereas the latter prints 
> only a single space at the beginning. To get the latter to act as the former 
> does, you must beta expand (I think that is the correct technical term) to 
> postpone the computation of printf " ":

This has been improved in 3.09.1 ... from the Changelog:

- Printf: better handling of partial applications of the
  printf functions.

        Objective Caml version 3.09.1

# List.iter (Printf.printf "%d ") [1;2;3] ;;
1 2 3 - : unit = ()
# List.iter (Printf.printf " %d") [1;2;3] ;;
 1 2 3- : unit = ()
# List.iter (fun n -> Printf.printf " %d" n) [1;2;3] ;;
 1 2 3- : unit = ()

Hurrah!  It always tripped me up :)

-- 
Anil Madhavapeddy                                 http://anil.recoil.org
University of Cambridge                          http://www.cl.cam.ac.uk

Re: [Caml-list] Pervasives or Printf module ?

[sejourne_kevin]

Anil Madhavapeddy a écrit :

>         Objective Caml version 3.09.1
> 
> # List.iter (Printf.printf "%d ") [1;2;3] ;;
> 1 2 3 - : unit = ()
> # List.iter (Printf.printf " %d") [1;2;3] ;;
>  1 2 3- : unit = ()
> # List.iter (fun n -> Printf.printf " %d" n) [1;2;3] ;;
>  1 2 3- : unit = ()
> 
> Hurrah!  It always tripped me up :)

Hurrah!


	

	
		
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Re: Pervasives or Printf module ?

[Vincenzo Ciancia]

Jon Harrop wrote:

> To get the latter to act as the former
> does, you must beta expand (I think that is the correct technical term)

In computer science literature, alpha conversion is usually the renaming of
a bound variable (fun x -> T = fun y -> T[y/x] provided that y does not
occurr in T), beta _reduction_ is function application ((fun x -> T)(T') =
T[T'/x]) , and _eta_ expansion is the term rewriting you're looking for. 

I don't know why, maybe it's just the order in which they were enumerated
originarily, but where are gamma, delta, epsilon, zeta rewrite rules? :)

V.

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Re: [Caml-list] Re: Pervasives or Printf module ?

[Remi Vanicat]

2006/1/22, Vincenzo Ciancia <vincenzo_yahoo_addressguard-gmane@yahoo.it>:
> Jon Harrop wrote:
>
> > To get the latter to act as the former
> > does, you must beta expand (I think that is the correct technical term)
>
> In computer science literature, alpha conversion is usually the renaming of
> a bound variable (fun x -> T = fun y -> T[y/x] provided that y does not
> occurr in T), beta _reduction_ is function application ((fun x -> T)(T') =
> T[T'/x]) , and _eta_ expansion is the term rewriting you're looking for.
>
> I don't know why, maybe it's just the order in which they were enumerated
> originarily, but where are gamma, delta, epsilon, zeta rewrite rules? :)

In the coq manual, one can see severall other rewriting rule, like
iota-reduction, delta-reduction and zeta-reduction.