Re: Practicalities of Ada for app development

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Mon, 11 Jun 2012 10:37:09 +0200, Dmitry A. Kazakov  
<mailbox@dmitry-kazakov.de> a écrit:

> On Sun, 10 Jun 2012 19:37:41 -0500, Nasser M. Abbasi wrote:
>
>> On 6/10/2012 2:47 PM, Dmitry A. Kazakov wrote:
>>
>>> It is not worth the efforts to bother about that,
>>> because, as I said, patterns is a bad idea in general.
>>
>> Have not followed the whole discussion here. But I just
>> wanted to mention on the above, is that Mathematica is based
>> on just this concept. Patterns.  It is really a pattern
>> replacement language at its core.
>>
>> For example, in Mathematica, when I define a function
>>
>> f[x_] := x^2
>>
>> x_ above means the pattern x.  On the right side, the
>> pattern named x is replaced by x raised to 2. That is
>> all what Mathematica does.
>>
>> When no more pattern matching replacement can be done, the final
>> resulting expression is evaluated and the result returned.
>
> It was called macro expansion in earlier days. An idea by margin more
> horrific than patterns in their original meaning (1. A language used to
> define a formal language; 2. Texture).

That's not horrific, that's pure mathematic. This equivalence by  
substitution is an important area of the core of all math formalisms, the  
establishment of formal proofs included.

What's horrific, is wild substitution, with no wellformedness and validity  
check of substituted expressions. Lack of substitution tracking may also  
help to provide a feeling of “horrific”.

What Nasser described, is expression substitution, not semantically  
neutral text substitution.

-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University