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NNTP-Posting-Date: Wed, 24 Jan 2007 02:07:16 -0600
From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: How come Ada isn't more popular?
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Date: Wed, 24 Jan 2007 09:07:15 +0100
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Xref: g2news2.google.com comp.lang.ada:8465
Date: 2007-01-24T09:07:15+01:00
List-Id: <comp.lang.ada>

kevin  cline writes:
> But the point was that expressiveness drives programmers to new
> languages, and Ada isn't particularly expressive.

On the contrary, I think that Ada is the most expressive language
around.  Consider:

procedure Set_Bit_In_Register (At_Address : in System.Address) is
   type Register is array (1 .. 32) of Boolean;
   pragma Pack (Register);
   for Register'Bit_Order use System.High_Order_First;
   pragma Volatile (Register);
   
   R : Register;
   for R'Address use At_Address;
begin
   Register (4) := True;
end;

versus

void set_bit_in_register (volatile unsigned long * at_address)
{
   *at_address |= 2 << 3;
}

The Ada version makes many more things explicit, that are assumed and
implicit in C; for example, the size of the register, the fact that
the parameter is an address and not a pointer (*), the endianness, and
which bit is being set.  As 64-bit architectures become prevalent, the
hidden assumption that C's "unsigned long" is 32 bits wide is more and
more likely to be incorrect.

(*) consider that when we increment the address by one, it then
references the next byte; whereas if we increment the pointer by one,
it points to the next "unsigned long", i.e. 2, 4 or 8 bytes and not 1
byte further.  C makes no distinction between addresses and pointers,
lacking expressiveness in a crucial area.

When calling the subprogram, we get:

Set_Bit_In_Register (At_Address => To_Address (16#DEADBEEF#));

versus

set_bit_in_register (0xDEADBEEF);

Again, at the call site, the Ada version gives more information to the
human programmer, i.e. is more expressive.

Expressiveness is not to be confused with conciseness.

-- 
Ludovic Brenta.