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From: Hibou57 (Yannick Duchêne) on 26 Oct 2009 22:36
On 27 oct, 02:14, "John B. Matthews" <nos...(a)nospam.invalid> wrote:
> with Ada.Text_IO; use Ada.Text_IO;
> with Ada.Text_IO.Text_Streams;
>
> procedure Copy is
>    Stream_Ptr : Text_Streams.Stream_Access;
>    C : Character;
> begin
>    Stream_Ptr := Text_Streams.Stream(Current_Input);
>    loop
>       Character'Read(Stream_Ptr, C);
>       Put(C);
>    end loop;
> exception
>    when End_Error => null;
> end Copy;
>
> --
> John B. Matthews
> trashgod at gmail dot com
> <http://sites.google.com/site/drjohnbmatthews>

The trouble with this, is that this force a look-ahead : an item must
be read to know if an item is available, and this can lead into
numerous logical traps (I prefer to keep distinct the action of
reading and testing availability of data).

May be this is finally really better to re-create a type to stand for
the standard input as binary, but what I do not like with this way, is
the possible lack of knowledge of some platforms, which is required
for implementations (For me, it will be OK for Windows, BSD, Linux,
but not the others... although in the mean time, I'm not sure I will
ever need it for other platforms).
From: John B. Matthews on 27 Oct 2009 12:13
In article
<a558f6b4-8f4c-459d-8706-4eb8125dae1e(a)w19g2000yqk.googlegroups.com>,
Hibou57 (Yannick Duchêne) <yannick_duchene(a)yahoo.fr> wrote:

> The trouble with this, is that this force a look-ahead : an item
> must be read to know if an item is available, and this can lead
> into numerous logical traps (I prefer to keep distinct the action
> of reading and testing availability of data).

Ah, I see your point. I recall this problem going back to the days of
UCSD Pascal, which distinguished between interactive and text type files
for this very reason. My use is to allow command line utilities to read
from standard input if no file name is supplied. For me, the data stream
invariably arrives via redirection or a pipe, so the problem does not
arise. For interactive programming, I typically use GtkAda.

This variation of Copy makes it easier to see what's happening.
Prefacing the loop with the End_Of_File predicate exposes the problem
for files with a terminal LF. If running interactively, control-D exits:

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Text_IO.Text_Streams;

procedure Copy is
Stream_Ptr : Text_Streams.Stream_Access;
C : Character;

function Hex(C : Character) return String is
H : constant String := "0123456789ABCDEF";
B : Natural := Character'Pos(C);
S : String(1 .. 4);
begin
S(1) := '[';
S(2) := H(B / 16 + 1);
S(3) := H(B mod 16 + 1);
S(4) := ']';
return S;
end Hex;

begin
Stream_Ptr := Text_Streams.Stream(Current_Input);
-- while not End_Of_File loop
loop
Character'Read(Stream_Ptr, C);
Put(Hex(C));
end loop;
exception
when End_Error => null;
end Copy;

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>
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