Types and Static Semantic Analysis

What is a type? A restriction on the possible interpretations of a segment of memory or other program construct. Useful for two reasons: Runtime optimization: earlier binding leads to fewer runtime decisions. E.g., Addition in C efficient because type of operands known. Error avoidance: prevent programmer from putting round peg in square hole. E.g., In Java, can't open a complex number, only a file. No: many languages operate just fine without them. Assembly languages usually view memory as undifferentiated array of bytes. Operators are typed, registers may be, data is not. Basic idea of stored-program computer is that programs be indistinguishable from data. Everything's a string in Tcl including numbers, lists, etc. Base types match typical processor Typical sizes: 8 16 32 64 char short int long float double Pointers (addresses) int *i; /* i is a pointer to an int */ char **j; /* j is a pointer to a pointer to a char */ Arrays char c[10]; /* c[0] ... c[9] are chars */ double a[10][3][2]; /* array of 10 arrays of 3 arrays of 2 doubles */ Functions /* function of two arguments returning a char */ char foo(int, double); A record is an object with a collection of fields, each with a potentially different type. In C,