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Re: Converting (more or less) arbitrary strings to valid variable names

From: Sergei Steshenko
Subject: Re: Converting (more or less) arbitrary strings to valid variable names
Date: Tue, 20 Nov 2012 06:06:57 -0800 (PST)

----- Original Message -----
> From: Bård Skaflestad <address@hidden>
> To: Sergei Steshenko <address@hidden>; "address@hidden" <address@hidden>
> Cc: 
> Sent: Tuesday, November 20, 2012 3:22 PM
> Subject: RE: Converting (more or less) arbitrary strings to valid variable 
> names
> Sergei,
> I'm afraid I don't fully understand your joke.  Maybe you wish to point 
> out that imposing needless restrictions on your own (working) environment 
> leads 
> to greef that is better avoided altogether.  I think that's an astute 
> observation and I won't argue the point.
> Like I said, the 'genvarname' function is at best a partial solution.  
> It has the advantage of being built into Octave but, as you say, there is no 
> direct support for recovering the original string from the 'genvarname' 
> output.  If reversibility is important then I suppose uu{en,de}code might be 
> a 
> better solution.
> On the other hand, you *could* create som sort of "translation table" 
> to preserve reversibility when dynamically forming structure field names 
> through 
> 'genvarname'.  For instance, you could do something like this (pseudo 
> code, glossing over a lot of detail, for instance what to do with repeated 
> strings):
>     symtab = {};
>     S = struct([]);
>     while (get data)
>          str = some string that uniquely identifies 'data';
>          vname = getvarname(str, symtab(:,1));
>          S.(vname) = data;
>          symtab = [ symtab ; { vname, str } ];
>     endwhile
> Then, whenever you require the identification string of a field name, say, 
> '_foo', you can extract it from 'symtab' using a statement such 
> as
>      str = symtab{strcmp(symtab(:,1), '_foo'), 2}
> It is certainly not pretty, but it is a general approach that can be adopted 
> to 
> many interesting situations.
> Sincerely,
> -- 
> Bård Skaflestad
> SINTEF ICT, Applied Mathematics
> ________________________________________
> From: Sergei Steshenko address@hidden
> Sent: 20 November 2012 03:23
> To: Bård Skaflestad; address@hidden
> Subject: Re: Converting (more or less) arbitrary strings to valid variable 
> names
> ----- Original Message -----
>>  From: Bård Skaflestad <address@hidden>
>>  To: "address@hidden" <address@hidden>
>>  Cc:
>>  Sent: Monday, November 19, 2012 11:47 PM
>>  Subject: Converting (more or less) arbitrary strings to valid variable 
> names
>>  All,
>>  In the long-running thread on "C-equivalent" structure (array)
>>  initialisation, someone asked of a way of converting an arbitrary string 
> into a
>>  valid variable name.  Unfortunately, I deleted the e-mail too early so I 
> cannot
>>  give proper attribution here.
>>  Still, I may be able to provide at least a partial answer to the inquiry.  
> The
>>  built-in function 'genvarname', present since at least Octave 
> 3.2.3,
>>  does solve some of this problem.  Here's an example
>>      > genvarname ("0  _f00  ba'r")
>>      ans = _0___f00__ba_r
>>  Obviously, the normal restrictions on variable names apply (string 
> restricted to
>>  "namelengthmax" characters being the most severe).
>>  I hope this helps a little bit.
>>  Sincerely,
>>  --
>>  Bård Skaflestad
>>  SINTEF ICT, Applied Mathematics
>>  _______________________________________________
>>  Help-octave mailing list
>>  address@hidden
> There is an old Jewish joke.
> The joke is a story about a poor Jew who had quite a hard life.
> So he, as the tradition prescribes, decided to consult the local rabbi.
> The rabbi said: "Buy a goat".
> The poor Jew didn't quite understand the essence of the advice, but followed 
> it.
> ...
> Several months later the poor Jew visited the rabbi again, this time simply 
> lamenting and crying about how unbearable his life had become.
> The rabbi said: "Sell the goat !".
> The poor Jew next day after selling the goat couldn't find enough words of 
> gratitude to thank the rabbi. The Jew couldn't belief the relief he found 
> after selling the goat.
> ...
> The problem with your function is that there may already be underscores in 
> otherwise illegal name, e.g. 'foo_ _bar'. So, there will be no easy way 
> to get back the original name.
> A much better way has already been suggested: uuencode -> uudecode - like 
> solutions. I.e. reversibility is guaranteed.
> But why do we need the "goat" in the first place ?
> I went carefully through 
> and did _not_ find there "struct arrays". So, this Matlab artifact 
> should be implemented in the least obtrusive for end user manner - only to 
> make 
> sure Matlab code runs in Octave.
> A _consistent_ hash table implementation is fair enough.
> Regards,
>   Sergei.

Please bottom-post.

The essence of the joke is that if someone complains about something, make that 
someone's life first even harder (make the complainer buy the goat - with whom 
the complainer lives in the same house), and then suggest to get rid of this 
new artificial difficulty ("sell the goat").

The newly acquired relief masks the original complaint.

So, further along the "goat" lines.

The original complaint is that

foo = struct
setfield(foo, "foo bar", 1)

works, but

foo = struct
foo.("foo bar") = 1

doesn't work.

The "goat" is adding check of hash key to make sure it's a valid identifier.

"Selling the goat" is getting rid of the check.

Fixing the original problem (the poor Jew's original complaint regarding his 
hard life) is making

foo.("foo bar") = 

work, additionally dropping worshiping Matlab original idiocy (Matlab, IIUC, 
requires struct fields to be valid identifiers.



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