Generate executable code for a target machine that is a faithful representation of the semantics of the source code Depends not only on the characteristics of the source language but also on detailed information about the target architecture, the structure of the runtime environment, and the operating system running on the target machine
Assuming two bytes for integers, four bytes for addresses, one byte for character and eight bytes for double-precision floating point, we would have the following offset values:
SLR(1), called simple LR(1) parsing, uses the DFA of sets of LR(0) items as constructed in the previous section SLR(1) increases the power of LR(0) parsing significant by using the next token in the input string – First, it consults the input token before a shift to make sure that an appropriate DFA transition exists
Main idea LL(1) Parsing uses an explicit stack rather than recursive calls to perform a parse An example: – a simple grammar for the strings of balanced parentheses: S→(S) S∣ε The following table shows the actions of a topdown parser given this grammar and the string ( )
The memory of a typical computer: A register area; Addressable Random access memory (RAM): A code area; A data area. The code area is fixed prior to execution, and can be visualized as follows:
Attributes – Any property of a programming language construct such as The data type of a variable The value of an expression The location of a variable in memory
Function of a Parser Takes the sequence of tokens produced by the scanner as its input and produces the syntax tree as its output. Parser Sequence of tokens Syntax-Tree
The Function of a Scanner Reading characters from the source code and form them into logical units called tokens Tokens are logical entities defined as an enumerated type – Typedef enum {IF, THEN, ELSE, PLUS, MINUS, NUM, ID,…} TokenType;
