Use of CFGs for Parsing OPEN

We can think of using CFGs to detect various language constructs in the token streams freed from simple
syntactic and semantic errors, as it is easier to describe the constructs with CFGs. But CFGs are hard to
apply practically. In this session we first exercise on simpler implementations of CFGs, and then
implement the FIRST and FOLLOW functions that facilitate efficient parsing algorithms for practical
problems.

Session 5 by Nafis Islam on Scribd

Detecting Simple Syntax Errors

Syntax errors are very common in source programs. Suppose, a given C source program has been scanned, filtered, lexically analyzed and tokenized as that were done in earlier sessions. In addition, line numbers have been assigned to the source code lines for generating proper error messages. As the first step to Syntax Analysis, we now perform detection of simple syntax errors like duplication of tokens except parentheses or braces, Unbalanced braces or parentheses problem, unmatched ‘else’ problem, etc

Session 4 by Nafis Islam on Scribd

Symbol Table Generation

A given C source program has been scanned, filtered and then lexically analyzed as it was done in Session 2. We have all the lexemes marked as different types of tokens like keywords, identifiers, operators, separators, parentheses, numbers, etc. We now get corrected the unknown lexemes first, and then generate a Symbol Table describing the features of the identifiers. Finally, we generate a modified token stream in accordance with the Symbol Table for processing by the next phase, that is, Syntactic Analysis

Session 3 by Nafis Islam on Scribd

Lexical Analysis

we have a C source program scanned and filtered as it was done in Session 1. We now take that modified file as input, and separate the lexemes first. We further recognize and mark the lexemes as different types of tokens like keywords, identifiers, operators, separators, parenthesis, numbers, etc.

Session 2 by Nafis Islam on Scribd

Scanning and Filtering a Source Program

You are given a C source program with single and multiple line comments. As the first step toward compilation you need to remove the comments and white space (extra spaces, tabs and newline characters). Develop a program that takes as input file the given source program and produces a filtered file as stated above. The program must also display both the files.

Session 1 by Nafis Islam on Scribd