JNTU B.Tech III COMPILER DESIGN Previous Question Paper (November/December - 2017 - R13)

A lexical analyser, or scanner, performs the following primary functions: it reads the input source code character by character to produce a stream of tokens, which are the meaningful units of the language such as keywords, identifiers, operators, and literals. It also removes white space, tabs, and newlines, and strips out comments from the source code. Additionally, it interacts with the symbol table to store information about identifiers and reports any lexical errors, such as illegal characters, to the compiler.

A leftmost derivation is a process where the leftmost non-terminal in the sentential form is replaced by the right-hand side of a production rule at each step. This process continues until the string consists entirely of terminals. It is often associated with top-down parsing strategies.

A rightmost derivation is a process where the rightmost non-terminal in the sentential form is replaced by the right-hand side of a production rule at each step. This process is the reverse of the leftmost derivation in terms of selection order and is typically associated with bottom-up parsing strategies, such as shift-reduce parsing.