Corona SDK error on lines 172 and 218, no filename, only question marks - error-handling

Question

Corona SDK simulator, version 2013.1137 (2013.6.7) is displaying the following error:
Corona Simulator Runtime error
File: ?
Attempt to perform arithmetic on field '?' (a function value)
stack traceback:
[C]: ?
?: in function <?:172>
?: in function <?:218>
The error is caused by the following code (main.lua):
local d1 = display.newCircle(0, 40, 10)
local gNonEmpty1 = display.newGroup()
gNonEmpty1:insert(display.newCircle(0, 70, 10))
local gEmpty1 = display.newGroup()
transition.to(d1, { time = 1000, x = 100 })
transition.to(gNonEmpty1, { time = 1000, x = 100 })
transition.to(gEmpty1, { time = 1000, x = 100 })
local d2 = display.newCircle(0, 150, 10)
local gNonEmpty2 = display.newGroup()
gNonEmpty2:insert(display.newCircle(0, 180, 10))
local gEmpty2 = display.newGroup()
transition.to(d2, { time = 1000, x = 100, transition = easing.outExpo })
transition.to(gNonEmpty2, { time = 1000, x = 100, transition = easing.outExpo })
transition.to(gEmpty2, { time = 1000, x = 100, transition = easing.outExpo })
local d3 = display.newCircle(0, 260, 10)
local gNonEmpty3 = display.newGroup()
gNonEmpty3:insert(display.newCircle(0, 290, 10))
local gEmpty3 = display.newGroup()
transition.to(d3, { time = 1000, x = 100, easing.outExpo })
transition.to(gNonEmpty3, { time = 1000, x = 100, easing.outExpo })
transition.to(gEmpty3, { time = 1000, x = 100, easing.outExpo })
The actual line causing the error is the second to last one:
transition.to(gNonEmpty3, { time = 1000, x = 100, easing.outExpo })
You can check it out by commenting it.
Corona documentation states that:
You should have at least one DisplayObject inserted into a
Display Group before you change or read any of the properties
of the group (e.g., x, y, setReferencePoint(), etc.).
Hence, it would be legit to expect some weird behavior when using transition.to
on gEmpty1, gEmpty2 or gEmpty3. As expected, the first two blocks of transition.to, for a total of six calls, behave the same, except for the easing
which is the default, easing.linear, for the first three calls, and easing.outExpo for the other three calls.
If you make a mistake in writing the transition.to calls, and you write something similar to the last three transition.to calls, where the transition = part is missing in the specification of the easing function, the surprising thing is that only the one that targets the non-empty group, gNonEmpty3 is responsible for the incomprehensible error message.
Questions
What should you do in Corona SDK when you get an error with no line numbers and no file names, but only question marks?
Why Corona SDK is not able to provide meaningful reporting beside two line numbers, 172 and 218?
Why this error is occurring? My theory is that the transition.to doesn't perform much error checking; if you target an empty group the error in specifying the easing function will go unnoticed; probably this is related with the fact empty groups properties should not be used, so maybe transition.to or its internal update callback finds out that the group is empty and simply returns without doing anything. Instead, for the non-empty group, the missing transition = causes some code to be triggered not necessarily the easing code, and in that code the actual error occurs.
config.lua
application = {
content = {
width = 320,
height = 480,
scale = "letterBox",
fps = 30
}
}
Original Post (obsolete)
I'm having a hard time at tracking down an error in Corona SDK.
The error causes the simulator to show the following message:
Corona Simulator Runtime error
File: ?
Attempt to perform arithmetic on field '?' (a function value)
stack traceback:
[C]: ?
?: in function <?:172>
?: in function <?:218>
How shall I interpret such message? I have no source files with
that many lines, by the way.
I have a file named Button.lua and line 41 seems to be involved
in raising an exception, although it is not raised from that
line. The line is:
button:insert(b1)
I wrapped that line between two prints:
print("Before", button, b1)
button:insert(b1)
print("After")
The following messages are printed in the simulator console:
Corona Simulator[9801:f03] Before table: 0x11daf4aa0 table: 0x1152363a0
Corona Simulator[9801:f03] After

Answer 1

Instead of your line:
transition.to(gNonEmpty3, { time = 1000, x = 100, easing.outExpo })
use :
transition.to(gNonEmpty3, { time = 1000, x = 100, transition = easing.outExpo })
In corona, such error message will occur when you have some wrong syntax or wrong logic. So, check for those issues first. Inserting print between the lines (that you used) is the best solution to find such error lines.
Keep Coding............. :)