[PD] (breaking symbols) was Re: find a list of numbers in a text file

Mathieu Bouchard matju at artengine.ca
Sat Sep 10 21:23:02 CEST 2011

On Wed, 7 Sep 2011, Hans-Christoph Steiner wrote:

> Yeah, I agree, I have no problem if someone wants to make an externals 
> that interprets 4+2 or "four" as 4, but it doesn't seem like something 
> that should be in the core.

Well, there would be no conflict if such a feature existed, because it 
would only happen when atom_getfloat() is called on a A_SYMBOL atom, and 
it would only happen when that symbol does not parse as a float (strtof 
would return 4 and report to have stopped parsing at the + sign, meaning 
that the whole symbol is not just 4).

However, nearly all programming languages that have implicit conversions 
would just let arithmetic stay out of the core.

Pd's [expr] and Tcl's [expr] are two notable weird exceptions, in which 
you can pass a symbol instead of a float, where the intention of the user 
was to allow using a float in the expression, yet you can pass 4+2 or 
whatever :

banging [expr $1] with $1=4+2 gives 6

banging [expr $1*-1] with $1=4+2 gives 4+2*-1 = 4-2 = 2 (really)

banging [expr ($1)*-1] with $1=4+2 gives 4

making it so that the argument is float is longer : you need to use $f1 
with an additional [f $1] (and in cases with multiple inlets, you may have 
to [loadbang] too, etc)

I suggest to stick with the simple stuff, that is, if you get "4+2" as a 
A_SYMBOL and atom_getfloat is used, you'd get « error: 4+2 can't be cast 
to float », because strtof() stopped before the end of the string. That's 
why you have to avoid atof... otherwise you'd cast 4+2 to 4 and give no 
error, and that's weird.

perl -e 'print("4+2"+0,"\n")' gives 4. (I don't approve.)

tcl's «expr "4+2" + 0» gives 6.

tcl's «expr {"4+2" + 0}» gives :
   can't use non-numeric string as operand of "+"

> About hex 0x form, that could conceivably fall under the "anything that 
> looks like a number is a float", as least for programmers.  In most 
> programming languages, 0x10 is just a number like 16.

Yeah, but it's a new incompatibility, just like changing the meaning of 
doublequotes. I don't mean that we shouldn't do it, just that it is 
something to be careful about.

Martin is not alone to use the 0x syntax for making symbols that represent 
ints bigger than what float32 can hold (which is limited to int25). I also 
use that for window-id of X11 screenshots, as used in 
http://gridflow.ca/help and also the Patch-dans-Patch series.

| Mathieu Bouchard ---- tél: +1.514.383.3801 ---- Villeray, Montréal, QC

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