Re: ADA Popularity Discussion Request

[jayessay <nospam@foo.com>]

Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de> writes:

> jayessay <nospam@foo.com> wrote:
> 
> : Yes, and they don't happen at runtime if pre and post are checked
> : during incremental development.  If you don't do this, then you will
> : likely have problems - just like if you don't get the types right in
> : static languages.
> 
> Is it really much more time efficient, if pre and post checking is done
> by an incrementing human? If so, how much?

Generally, yes.  For two general reasons: 1. you are always sure of
the logic as well as the type consistency 2. You don't have global
"system integration" issues as each incremental step subsumes an
integration aspect.



> : Your explanation above does not cover the logic error.  I don't see
> : right off how modular types catch that.
> 
> See below, there isn't a logic error, only a typo.

No, I'm not talking about the typo in the advance function.  I'm
talking about the logic error in the Hext function itself!

> 
> : with Text_Io; use Text_Io;
> : 
> : procedure Foo is
> : 
> :   type Hex_Num is mod 16;
> : 
> :   function Hext (N : Integer) return Hex_Num is
> :   begin
> :      -- == (1+ (n mod 16)), which is the logic error.
>                                            ^^^^^^^^^^^^ not really, see below
> :      return Hex_Num(1 + (N mod Hex_Num'Modulus));
> :   end Hext;
> : 
> : begin
> :   for I in 0..20 loop
> :      Put_Line("Answer is: " & Hex_Num'Image(Hext(i)));
>       Put_Line("Answer is: " & Integer'Image(Hext(i)));
> :   end loop;
> : end;
> 
> In the Lisp example there was a "typo context". "next" should have
> been where "hext" was actually typed in the Lisp example

That's not the logic error.  The logic error is that Hext is broken
due to the incorrect expression at the line noted above.


> Therefore, an integer number was actually wanted ("next"), not
> a hex number ("hext").

> So there must be an Integer'image reflecting the logic/expectation
> ("next") not a Hex_Num'image (typo "hext").
> The error is caught by the compiler.
> 
>     15.       Put_Line("Answer is: " & Integer'Image(Hext(i)));
>                                                      |
>         >>> expected type "Standard.Integer"
>         >>> found type "Hex_Num" defined at line 4


No. This would be a different (brain fart) type of error.  The logic
error is in Hext - it does not correctly compute the residue class
defined by Hex_Num!!!  This is shown by the Ada RT raising constraint
error - even though the compiler didn't (indeed _couldn't_ complain
about the definition!!!).

/Jon


-- 
'j' - a n t h o n y at romeo/charley/november com