Structure First Consists Of
	Nothing;
EndStructure

Structure Second Consists Of
	Nothing;
EndStructure

Function main(Integer32 a, Integer32 b) Which Returns Nothing Does
	InstantiateStructure First firstStructure;
	InstantiateStructure Second secondStructure;
	InstantiateStructure Second thirdStructure := (a > b) ? firstStructure : secondStructure; // This line contains the error.
EndFunction

Running the tests...
All the tests passed in 4 milliseconds.
Reading the file "debug.aec"...
All characters read in 0 milliseconds.
Tokenizing the program...
Finished tokenizing the program in 0 milliseconds.
I have made a forum thread about how to speed up the tokenizer,
in case you are interested:
https://www.forum.hr/showthread.php?t=1243509
Parsing the program...
Finished parsing the program in 0 milliseconds.
Compiling the program...
Line 10, Column 29, Internal compiler error: Some part of the compiler attempted to compile an array with size less than 1, which doesn't make sense. Throwing an exception!
Internal compiler error: Uncaught exception in the compiler: St13runtime_error: Compiling an array of negative size!
If you have time, please report this to me on GitHub as an issue:
https://github.com/FlatAssembler/AECforWebAssembly/issues