That PDF doesn't look like the source for an operating system, but rather a 2 pass compiler. There are references to data types (including Complex) on p.6 and various hand written comments, such as "procedure" on p.2 and "return to pass 2" on p.19. The following page looks like a lexer table and might be the reserved words. Then on line 1658 (lost track of page #) "const expression, like (2^40-1) are evaluated at compile time". Based on how the later comments are written, I think they were added by someone trying to understand the compiler.
