 Whereas the Turing machine is and was a fundamental theoretical model delimiting what is possible and not on the general level, it did not have a real impact on the syntax and semantics of programming languages. In that context it were rather λ-calculus and Post production systems that had an effect (though also here one should be careful in overstating the influence of a formal model on a programming practice). In fact, Turing machines were often regarded as machine models rather than as a model for programming: