We define type checkers to define which programs are well-typed and which are not. Throughout the book we write small interpreters for toy languages, and in Chapter8we write a principled compiler. Daniel P. Friedman is CONTENTSBibliographic notesData TypesTypes ming languages, including Python, Java, and C, are fundamentally imperative in nature: inspired by the Turing machine model of computation, programs in these languages are ICI Designed by Tim Long in, ICI is a general purpose interprete