Regular expressions

[Christian Gollwitzer]

Am 04.11.15 um 04:48 schrieb Steven D'Aprano:
> On Wednesday 04 November 2015 11:33, rurpy at yahoo.com wrote:
>
>>> Not quite.  Core language concepts like ifs, loops, functions,
>>> variables, slicing, etc are the socket wrenches of the programmer's
>>> toolbox.  Regexs are like an electric impact socket wrench.  You can do
>>> the same work without it, but in many cases it's slower. But you have to
>>> learn the other hand tools first in order to really use the electric
>>> driver properly (understanding torques, direction of threads, etc), lest
>>> you wonder why you're breaking off so many bolts with the torque of the
>>> impact drive.
>>
>> I consider regexs more fundemental
>
> I'm sure that there are people who consider the International Space Station
> more fundamental than the lever, the wedge and the hammer, but they would be
> wrong too.
>
> Given primitives for branching, loops and variables, you can build support
> for regexes. Given regexes, how would you build support for variables?
>
> Of course, you could easily prove me wrong.

You *know* that they are not equivalent, I assume? regexes are 
equivalent to finite state machines, which are less powerful than Turing 
machines, and even less powerful than stack machines. You can't even 
construct a regexp which validates, if parentheses are balanced.

What rurpy meant, was that regexes can surface to a computer user 
earlier than variables and branches; a user who does not go into the 
depth to actually program the machine, might still encounter them in a 
text editor or database engine. Even some web forms allow some limited 
form, like e.g. the DVD rental here or Google.

	Christian