I have run into the symbol
multiple times. What is this symbol, and what is it designed to indicate? All I could find is that FE indicates the front-end, but it's unfortunately a very Ungoogleable term. I believe that it's not something I should ever "see" on the front, but I'm guessing it represents some sort of display element. Perhaps "this object is un-representable to the front end" or something like?
To be clear, I'm not asking for aid in fixing my program so as to not produce this output. This is a question about the definition of the symbol, out of purely intellectual curiosity.
Edit: After a long while debugging the application, I've managed to reduce the problematic code that caused this happen. See, it was doing some fuzzy logic computations, and various computations were being represented using
If statements. For instance
If[True,a,b] evaluates to
a always, then
If[var,a,b] could be used to represent a fuzzy mixture of
b. (This was not my design decision.) Then the computations were implemented as different overloads of
If. Naturally, this meant
If as well.
Through a chain of some slightly-off
:=, there was some code that ended up running under certain circumstances to evaluate to:
Unprotect[If]; Unprotect[If]; If[True,a_,b_] := If[RandomReal > 0.5,a,b];
I think it's pretty obvious how this could could lead to some weird problems down the line. As a minimal case, run the above, followed by
If[True,1,2]. I tested on a few different versions of Mathematica on different machines, it seems to consistently produce
2, with a "Full output could not be displayed" warning. Pressing "Show full output" 3 times then waiting 15 minutes caused the output to re-render as "FE`None".