Hi everyone!

I bumped recently into this difficulty and I am not sure if this is a bug or a feature: when I create a message with contents

;
pd-test.pd obj 10 10 expr $f1/$1;
pd-test.pd obj 110 10 expr $f1 / $1;

and I save and re-open this patch, the message reads

;
pd-test.pd obj 10 10 expr $f1/\$1;
pd-test.pd obj 110 10 expr $f1 / $1;

which is obviously interpreted differently because of the inserted backslash before the first $1. Apparently the space prevents Pd from inserting this backslash in the second line of the message. Is this the expected behavior? If so, is there a specification regarding escaped sequences and/or dollar signs appearing at the beginning or middle of symbols that explains it?

I would like to emphasize that my question refers exclusively to how PdFileFormat encodes and decodes Pd messages in general, and bears no relationship with the [expr] object or with dynamic patching (though the reference to them is obvious).

A follow-up difficulty has to do with the internal representation of the first message in the saved file, which is:

#X msg 10 135 ; pd-test.pd obj 10 10 expr $f1/\$1 ; pd-test.pd obj 110 10 expr $f1 / \$1 ;;

where Pd interprets the backslash in the symbol $f1/\$1 as an independent character. On the other hand, when I duplicate this message in Pd, the internal representation for the 2nd copy becomes

#X msg 10 135 ; pd-test.pd obj 10 10 expr $f1/\\\$1 ; pd-test.pd obj 110 10 expr $f1 / \$1 ;;

denoting that an independent backslash character would require to be backslash-escaped in the PdFileFormat. The fact that these two latter versions (with \$1 and \\\$1 in the file) appear and behave the same in the patch also struck me as unintuitive, so if anyone may shed some light into this I'd really appreciate.

Thanks in advance for your help!

@marcelo It is always hard to read posts about the backslash on the forum because they are dropped in the same manner that they used to be in Pd (illegal previously in a patch window...... we never saw them).
Keycode 92 could not be typed...... it was always dropped.

It does have to do with dynamic (unsupported) patching in that spaces are always used in Pd to determine the "next atom"..... so the formula for [expr] needs to have its elements separated by whitespace to denote new arguments, as atoms grouped together in a message will always be converted to a symbol.

Conjecture......
$f1/$1 would normally be joined as a string and interpreted from an incoming message to your message box (or give symbol $f1/0 when banged), but when the [expr] is dynamically created that cannot be the case as the dollar must be literal.
Somewhere in Pd or the tcl will be the code that fudges a solution.
Resistance to the use of escape codes has produced some quite contorted coding.
David.

Thanks David @whale-av for taking the time to help me, and also for pointing out that my message was almost unintelligible due to the dropped backslashes. What a nightmare... I edited it to make it look the same way I typed it, for future reference.

I presumed some contorted coding was involved in this difficulty, but if it also involves tcl then the situation is probably hopeless. Fortunately inserting all those whitespaces seems at least to provide a viable workaround.