C Program Construct Expression Tree
Lexical Analyzer recognizes the tokens from series of characters. A “C” program consists of tokens such as Identifiers, Integers, Floating Point Numbers, Punctuation symbols, relational and logical and arithmetic operators, keywords and comments (to be removed). To identify these tokens, lexical analyzer needs the specification of each of these symbols. The set of words belonging to a particular token type is a regular language. Hence each of these token types can be specified using regular expressions. For example, consider the token Identifier. In most of the programming languages, an identifier is a word which begins with an alphabet (capital or small) followed by zero or more letters or digits (0.9).
This can be defined by the regular expression. DFA is constructed directly from an augmented regular expression ( r )#. We begin by constructing a syntax tree T for ( r ) # and then we compute four functions Nullable, Firstpos, Lastpos and Followpos. The functions Nullable, Firstpos, Lastpos are defined on the nodes of a syntax tree and are used to compute Followpos which is defined on set of positions. We can short circuit the construction of NFA by building the DFA whose states correspond to the sets of positions in the tree. Positions, in particular, encode the information regarding when one position can follow another. Each symbol in an input string to a DFA can be matched by certain positions.
C Program Construct Expression Tree Program
An input symbol ‘c’ can only be matched by positions at which there is a ‘c’ but not every position with a ‘c’ can necessarily match a particular occurrences of ‘c’ in input stream.