Need help with this!PA 2 Description 1 CS 280 Programming Language Concepts Spring 2023 Programming...

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Need help with this!PA 2 Description 1 CS 280 Programming Language Concepts Spring 2023 Programming Assignment 2 Building a Recursive-Descent Parser for SPL Language Programming Assignment 2 ◼ Objectives  building a recursive-descent parser for our simple language. ◼ Notes:  Read the assignment carefully to understand it.  Understand the functionality of each function, and the required error messages to be printed out. ◼ The syntax rules of the SPL programming language are given below using EBNF notations. 3 SPL Language Definition 1. Prog ::= StmtList 2. StmtList ::= Stmt ;{ Stmt; } 3. Stmt ::= AssignStme | WriteLnStmt | IfStmt 4. WriteLnStmt ::= writeln (ExprList) 5. IfStmt ::= if (Expr) ‘{‘ StmtList ‘}’ [ else ‘{‘ StmtList ‘}’ ] 6. AssignStmt ::= Var = Expr 7. Var ::= NIDENT | SIDENT 8. ExprList ::= Expr { , Expr } 9. Expr ::= RelExpr [(-eq|==) RelExpr ] 10. RelExpr ::= AddExpr [ ( -lt | -gt |  ) AddExpr ] 11. AddExpr :: MultExpr { ( + | - | .) MultExpr } 12. MultExpr ::= ExponExpr { ( * | / | **) ExponExpr } 13. ExponExpr ::= UnaryExpr { ^ UnaryExpr } 14. UnaryExpr ::= [( - | + )] PrimaryExpr 15. PrimaryExpr ::= IDENT | SIDENT | NIDENT | ICONST | RCONST | SCONST | (Expr) 4 Example Program of SPL Language #Clean program with nested if statement $r = 50; @flag = 'true'; if (@flag -lt 'true' ) { $y_1 = 5; if($y_1 > 4) { @flag = 'hello'; $y_1 = $y_1 + 1; } else { @flag = 'goodbye'; $y_1 = $y_1 -1; }; writeln ('Value = ', $r ,'$y_1 = ', @flag); } else { $y_1 = (7.5); @flag = 'goodbye'; }; $r = $r + @flag; 5 Description of the SPL Language ◼ The language has two types: Numeric, and String. ◼ The SPL language does not have explicit declaration statements. However, variables are implicitly declared as Numeric type by a variable name starting with “$”, or as String type by a variable name starting with “@”. ◼ All SPL variables must first be initialized by an assignment statement before being used. ◼ The precedence rules of operators in the language are as shown in the table of operators’ precedence levels. ◼ The PLUS, MINUS, MULT, DIV, CAT, and SREPEAT operators are left associative. 6 Table of Operators Precedence Levels 7 Precedence Operator Description Associativity 1 Unary +, - Unary plus, and minus, Right-to-Left 2 ^ Exponent Right-to-Left 3 *, /, ** Multiplication, Division,  and string repetition Left-to-Right 4 +, -, . (Dot) Addition, Subtraction, and String concatenation Left-to-Right 5  -gt, -lt • Numeric Relational  • String Relational  (no cascading) 6 == -eq • Numeric Equality  • String Equality (no cascading) Description of the SPL Language ◼ The binary operations of numeric operators as addition, subtraction, multiplication, and division are performed upon two numeric operands. While the binary string operator for concatenation is performed upon two string operands. If one of the operands does not match the type of the operator, that operand is automatically converted to the type of the operator. ◼ Similarly, numeric relational and equality operators (==, ) operate upon two numeric type operands. While, string relational and equality operators (-eq, -lt, -gt) operate upon two string type operands. The evaluation of a relational or equality expression, produces either a true or false value. If one of the operands does not match the type of the operator, that operand is automatically converted to the type of the operator. For all relational and equality operators, no cascading is allowed. 8 Description of the SPL Language ◼ The exponent operator is applied on a numeric type operand, and the exponent value must be a numeric type value. No automatic conversion to numeric type operand is applied in case of an expression with exponent operator. Note that, exponent operators follow right-to-left association. ◼ The binary operation for string repetition (**) operates upon a string operand as the first operand, where the second operand must be a numeric expression of integer value. ◼ The unary sign operators (+ or -) are applied upon unary numeric type operands only. 9 Description of the SPL Language ◼ An IfStmt evaluates a logical expression (Expr) as a condition. If the logical condition value is true, then the StmtList in the If-clause are executed, otherwise they are not. An else clause for an IfSmt is optional. Therefore, If an Else-clause is defined, the StmtList in the Else-clause are executed when the logical condition value is false. ◼ A WriteLnStmt evaluates the list of expressions (ExprList), and prints their values in order from left to right followed by a newline. 10 Description of the SPL Language ◼ The ASSOP operator (=) in the AssignStmt assigns a value to a variable. It evaluates the Expr on the right-hand side and saves its value in a memory location associated with the left- hand side variable (Var). A left-hand side variable of a Numeric type must be assigned a numeric value. While a left- hand side variable of a String type must be assigned a string value. Type conversion must be automatically applied if the right-hand side value of the evaluated expression does not match the type of the left-hand side variable. ◼ It is an error to use a variable in an expression before it has been assigned. 11 Recursive-Descent Parser ◼ The parser includes one function per syntactic rule or nonterminal. ◼ Each function recognizes the right hand side of the rule.  If the function needs to read a token, it can read it using getNextToken().  If the function needs a nonterminal symbol, it calls the function for that nonterminal symbol. ◼ There is no explicit generation of a parse tree to be implemented. However the recursive-descent parser is tracing the parse tree implicitly for the input program.  Use printout statements to enable you to debug your implementation of the parser. Notice, this is not part of the assignment. 12 Given Files ◼ “lex.h” ◼ “lex.cpp” (you can use your implementation, or copy and use my lexical analyzer when I publish it). ◼ “parser.h” ◼ “prog2.cpp”: main function as a driver program for testing your parser implementation. ◼ “parser.cpp” file with definitions and the implementation of some functions of the parser. 13 parser.h ◼ All recursive-descent functions take a reference to an input stream, and a line number, and return a Boolean value.  The value returned is false if the call to the function has detected a syntax error. Otherwise, it is true.  PrimaryExpr function takes an extra parameter for the passed sign operator. Note, the function will make use of the sign in the evaluation of expressions when the interpreter will be built. 14 parser.h ◼ Functions’ prototypes in “parser.h” extern bool Prog(istream& in, int& line); extern bool StmtList(istream& in, int& line); extern bool Stmt(istream& in, int& line); extern bool SimpleStmt(istream& in, int& line); extern bool SimpleIfStmt(istream& in, int& line); extern bool WritelnStmt(istream& in, int& line); extern bool IfStmt(istream& in, int& line); extern bool AssignStmt(istream& in, int& line); extern bool Var(istream& in, int& line); extern bool ExprList(istream& in, int& line); extern bool Expr(istream& in, int& line); extern bool RelExpr(istream& in, int& line); extern bool AddExpr(istream& in, int& line); extern bool MultExpr(istream& in, int& line); extern bool ExponExpr(istream& in, int& line); extern bool UnaryExpr(istream& in, int& line); extern bool PrimaryExpr(istream& in, int& line, int sign); 15 parser.cpp ◼ Token Lookahead  Remember that we need to have one token for looking ahead.  A mechanism is provided through functions that call the existing getNextToken, and include the pushback functionality. This is called a “wrapper”.  Wrapper for lookahead is given in “parser.cpp”. 16 namespace Parser { bool pushed_back = false; LexItem pushed_token; static LexItem GetNextToken(istream& in, int& line){ if( pushed_back ) { pushed_back = false; return pushed_token; } return getNextToken(in, line); } static void PushBackToken(LexItem & t) { if( pushed_back ) { abort(); } pushed_back = true; pushed_token = t; } } 17 Wrapper for lookahead (given in “parser.cpp”) ◼ To get a token:  Parser::GetNextToken(in, line) ◼ To push back a token:  Parser::PushBackToken(t) ◼ NOTE: after push back, the next time you call Parser::GetNextToken(), you will retrieve the pushed-back token. ◼ NOTE: an exception is thrown if you push back more than once (using abort()). 18 parser.cpp ◼ A map container that keeps a record of the defined variables in the parsed program, defined as: map defVar;  The key of the defVar is a variable name, and the value is a Boolean that is set to true when the first time the variable has been declared in a declaration statement, otherwise it is false.  The use of a variable that has not been declared is an error.  It is an error to redefine a variable. 19 parser.cpp ◼ Static int variable for counting errors, called error_count and a function to return its value, called ErrCount(). static int error_count = 0; int ErrCount(){ return error_count; } ◼ A function definition for handling the display of error messages, called ParserError. void ParseError(int line, string msg){ ++error_count; cout

PA 2 Description1CS 280Programming Language ConceptsSpring 2023Programming Assignment 2Building a Recursive-Descent Parser for SPL LanguageProgramming Assignment 2◼ Objectives...

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