It's kind of fun thinking of "bootstrapping" a trusted compiler from some old sources. Like some sort of master handing down their tools to the apprentice.
"Now, I bestow upon you my most trusted C compiler...artisanally compiled from ancient scrolls using only an 8088 chip"
The oldest thing I have is also the first C compiler I ever used, the ECO-C88 on 5.25" floppy.
p.s. Also I just looked up that Ken Thompson paper, and it credits "[4] Unknown Air Force Document" for the idea (!!)
@meejah Also, this: http://bootstrappable.org/projects.html
(The one I am interested the most is this one, which unfortunately is going to be hard - https://elephly.net/posts/2017-01-09-bootstrapping-haskell-part-1.html)
@meejah A better technical answer is here on the GHC situation: https://www.joachim-breitner.de/blog/748-Thoughts_on_bootstrapping_GHC
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@meejah :-) GHC is written in GHC itself. Early GHC was written in LazyML, I think. Some sources of LazyML are available, but I don't know if a version of GHC that can compile with LazyML is available. I haven't been able to dig out very old versions of GHC. Most of the ftp sites are dead. Internet Archive does not have anything from them.. so it is a dead end there.