Parser analyzes a code syntactically according to the rules of the language's grammar. The parsing phase determines if the input code can be used to form a string of tokens according to the defined grammar. A parse tree is constructed in this phase. Parser defines functions to organize language into a data structure called AST. The parser defined in this recipe uses a recursive decent parser technique which is a top-down parser, and uses mutually recursive functions to build the AST.
We must have the custom-defined language, that is the TOY language in this case, and also a stream of tokens generated by the lexer.
Define some basic value holders in our TOY parser as shown in the following:
Open the
toy.cppfile as follows:$ vi toy.cpp
Define a global static variable to hold the current token from the lexer as follows:
static int Current_token;
Define a function to get the next token from the input stream from the lexer as follows:
static void next_token...