BooTsTraPPing (CompilEr)

All this may seem to be skirting around a really nasty issue - how might the first high-level
language have been implemented? In ASSEMBLER? But then how was the assembler for
ASSEMBLER produced?

A full assembler is itself a major piece of software, albeit rather simple when compared with a
compiler for a really high level language, as we shall see. It is, however, quite common to define
one language as a subset of another, so that subset 1 is contained in subset 2 which in turn is
contained in subset 3 and so on, that is:

 

 

One might first write an assembler for subset 1 of ASSEMBLER in machine code, perhaps on a
load-and-go basis (more likely one writes in ASSEMBLER, and then hand translates it into
machine code). This subset assembler program might, perhaps, do very little other than convert
mnemonic opcodes into binary form. One might then write an assembler for subset 2 of
ASSEMBLER in subset 1 of ASSEMBLER, and so on.

This process, by which a simple language is used to translate a more complicated program, which
in turn may handle an even more complicated program and so on, is known as bootstrapping, by
analogy with the idea that it might be possible to lift oneself off the ground by tugging at one’s boot-straps.