It's my understanding that the Apple //e Oregon Trail was written in 6502 assembly. In comparison, the predecessors to Oregon Trail were written in BASIC such as the earlier Apple //e game simply called Oregon as well as the even earlier mainframe versions.
I do know for a fact that Oregon Trail was shipped as binary code because I remember trying to edit it (and failing, though I was incompetent at assembly as a child). In comparison, I successfully modified the earlier game Oregon since it was written in BASIC. Also, when you compare the graphic perform of Oregon (poor and slow, but on par for Apple BASIC) vs Oregon Trail (fast and on par with other games), Oregon Trail was definitely not using the Apple BASIC interpreter. Maybe they wrote Oregon Trail in BASIC and utilized a compiler, but I don't recall compilers be used much for 8-bit computers back in the day which is why I suspect it was written in 6502 assembly instead.
The above page doesn't say directly but this quote indicates that the main game was still BASIC with graphics, animations, and maybe UI in assembly. [And they did have BASIC compilers for the Apple II back in 1984.]
"To write a program entirely in assembly language was very difficult and time consuming, compared to writing a program in BASIC. But Applesoft allowed you to mix the two languages, through a technique called & hooks. You could write most of the program in Applesoft, and then use an & hook to call an assembly language subroutine whenever you needed to display a paragraph of text or an image on the screen."
Still it doesn't tell us anything about this handheld version. The 1985 Apple II version is very similar to the 1990 DOS version and very different than previous versions that were done in a much more limited version of BASIC. The Intellivision version was likely ported from the older 1978/79 game as I don't think the BASIC source to the 1985 version is available. I'm assuming the 1985 version is still copyrighted and this handheld is licensed with access to the source code a possibility.
Edited by mr_me, Fri Mar 2, 2018 6:48 AM.