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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: a new language, designed for safety !
Date: Mon, 23 Jun 2014 19:04:23 +0200
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Date: 2014-06-23T19:04:23+02:00
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On Mon, 23 Jun 2014 10:17:47 -0400, Peter Chapin wrote:

> On 2014-06-22 20:51, Shark8 wrote:
> 
>> IIRC, Lisp's Error-handling can ensure that types are consistent, even
>> though the language itself is dynamically typed.
> 
> It's quite normal for dynamic languages to do type checking, they just
> do it at runtime (dynamically). That's practically the definition of
> "dynamic language" to my mind. It partly accounts for the flexibility of
> such languages as well as their sometimes sluggish performance.

and bugs, because this is not type checking. It is checking for a subtype
constraint. A type in such a language corresponds to Ada's subtype. The
check for an operation to exist corresponds to Ada's constraint check or
tag check as in an operation with two controlled arguments.

Just like in Ada, if the failure of the check means a bug, then it is a
bug, because you are at run-time and you didn't anticipate it. BOOM!

No dynamic can ever prevent a bug. It is just too late. What a dynamic
check can is to reduce the damage of a bug. E.g. to blow up the rocket
before it landed on the developer's head.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de