Greenspun's Rule basically covers that. Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementa

Greenspun's Rule basically covers that. Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp. Although nowadays the art of programming is maturing enough that the inner platform sometimes is deliberately designed and well specified.