See the Chicken and Egg section of the Wikipedia page:
If one needs a compiler for language X to obtain a compiler for language X (which is written in language X), how did the first compiler get written? Possible methods to solving this chicken or the egg problem include:
- Implementing an interpreter or compiler for language X in language Y. Niklaus Wirth reported that he wrote the first Pascal compiler in Fortran.
- Another interpreter or compiler for X has already been written in another language Y; this is how Scheme is often bootstrapped.
- Earlier versions of the compiler were written in a subset of X for which there existed some other compiler; this is how some supersets of Java, Haskell, and the initial Free Pascal compiler are bootstrapped.
- The compiler for X is cross compiled from another architecture where there exists a compiler for X; this is how compilers for C are usually ported to other platforms. Also this is the method used for Free Pascal after the initial bootstrap.
- Writing the compiler in X; then hand-compiling it from source (most likely in a non-optimized way) and running that on the code to get an optimized compiler. Donald Knuth used this for his WEB literate programming system.
