The Colossal Cave Adventure as a literate program by Don Knuth

Knuth says: "Many of the phrases in the following documentation have been lifted directly from comments in the FORTRAN code. Please regard me as merely a translator of the program, not as an author. I thank Don Woods for helping me check the validity of this translation."

And also:

"By the way, if you don’t like goto statements, don’t read this. (And don’t read any other programs that simulate multistate systems.)"

Even computer science marches on: Thanks to tail call elimination, we can write code that's clean and safe, and will compile to gotos.

This is the first example I always point to when they ask about Literate Programming.