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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: The state of functional programming
Newsgroups: comp.lang.ada
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Date: Fri, 30 Jul 2010 11:29:31 +0200
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Date: 2010-07-30T11:29:31+02:00
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On Fri, 30 Jul 2010 12:17:29 +0300, Niklas Holsti wrote:

> Dmitry A. Kazakov wrote:
>> On Thu, 29 Jul 2010 21:01:35 +0000 (UTC), Warren wrote:
>> 
>>> Dmitry A. Kazakov expounded in
>>> news:17hhchqy1a2si.1akul43vk1sd9.dlg@40tude.net: 
>>>
>>>> On Thu, 29 Jul 2010 19:19:49 +0000 (UTC), Warren wrote:
>> 
>>>>> But FP cannot always solve that "problem".
>>>> Same in Ada. Not every legal Ada program is compilable. 
>>> If an Ada program doesn't compile, then the programmer
>>> hasn't spelled out the "how" correctly has he?  
>> 
>>    X : constant := 2**(2**(2**(2**9999_9999))) + 1:
>> 
>> is pretty much clear "how", legal, but not compilable.
> 
> ... because the binary representation of the value of X needs too many 
> bits, you mean? But I don't think that a compiler is required to 
> represent the value in binary form *at compile time*; it could use a 
> formulaic representation, which needs only a small amount of memory, as 
> shown by your source line. Depending on how X is used in the rest of the 
> program, this could make it possible to compile the program.

Yes, but you cannot find a representation which would work for any legal
expression. I.e. whatever representation the compiler uses, it is always
possible to write a legal program that would break it. E.g:

    X : constant := 2**(3**(2**(3**9999_9999))) + 1:
    Y : constant := 3**(2**(5**(2**8999_9979))) - 1:
    C : constant Boolean := X > Y;

> Of course I agree that a normal Ada compiler will not be able to compile 
> such things.

The above expression is supposed to break representations used by "normal
compilers".

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