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parser.cpp
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791 lines (642 loc) · 14.6 KB
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/* Implementation of Recursive-Descent Parser
* for the SFort95 Language
* parser.cpp
*/
#include "parser.h"
map<string, bool> defVar;
map<string, Token> SymTable;
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;
}
}
static int error_count = 0;
int ErrCount()
{
return error_count;
}
void ParseError(int line, string msg)
{
++error_count;
cout << line << ": " << msg << endl;
}
bool IdentList(istream& in, int& line);
//Program is: Prog = PROGRAM IDENT {Decl} {Stmt} END PROGRAM IDENT
bool Prog(istream& in, int& line)
{
bool dl = false, sl = false;
LexItem tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == PROGRAM) {
tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == IDENT) {
dl = Decl(in, line);
if( !dl )
{
ParseError(line, "Incorrect Declaration in Program");
return false;
}
sl = Stmt(in, line);
if( !sl )
{
ParseError(line, "Incorrect Statement in program");
return false;
}
tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == END) {
tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == PROGRAM) {
tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == IDENT) {
cout << "(DONE)" << endl;
return true;
}
else
{
ParseError(line, "Missing Program Name");
return false;
}
}
else
{
ParseError(line, "Missing PROGRAM at the End");
return false;
}
}
else
{
ParseError(line, "Missing END of Program");
return false;
}
}
else
{
ParseError(line, "Missing Program name");
return false;
}
}
else if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
else
{
ParseError(line, "Missing Program keyword");
return false;
}
}
//Decl ::= Type :: VarList
//Type ::= INTEGER | REAL | CHARARACTER [(LEN = ICONST)]
bool Decl(istream& in, int& line) {
bool status = false;
LexItem tok;
string strLen;
LexItem t = Parser::GetNextToken(in, line);
if(t == INTEGER || t == REAL || t == CHARACTER ) {
tok = t;
tok = Parser::GetNextToken(in, line);
if (tok.GetToken() == DCOLON) {
status = VarList(in, line);
if (status)
{
status = Decl(in, line);
if(!status)
{
ParseError(line, "Declaration Syntactic Error.");
return false;
}
return status;
}
else
{
ParseError(line, "Missing Variables List.");
return false;
}
}
else if(t == CHARACTER && tok.GetToken() == LPAREN)
{
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == LEN)
{
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ASSOP)
{
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ICONST)
{
strLen = tok.GetLexeme();
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == RPAREN)
{
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == DCOLON)
{
status = VarList(in, line);
if (status)
{
cout << "Definition of Strings with length of " << strLen << " in declaration statement." << endl;
status = Decl(in, line);
if(!status)
{
ParseError(line, "Declaration Syntactic Error.");
return false;
}
return status;
}
else
{
ParseError(line, "Missing Variables List.");
return false;
}
}
}
else
{
ParseError(line, "Missing Right Parenthesis for String Length definition.");
return false;
}
}
else
{
ParseError(line, "Incorrect Initialization of a String Length");
return false;
}
}
}
}
else
{
ParseError(line, "Missing Double Colons");
return false;
}
}
Parser::PushBackToken(t);
return true;
}//End of Decl
//Stmt ::= AssigStmt | BlockIfStmt | PrintStmt | SimpleIfStmt
bool Stmt(istream& in, int& line) {
bool status;
LexItem t = Parser::GetNextToken(in, line);
switch( t.GetToken() ) {
case PRINT:
status = PrintStmt(in, line);
if(status)
status = Stmt(in, line);
break;
case IF:
status = BlockIfStmt(in, line);
if(status)
status = Stmt(in, line);
break;
case IDENT:
Parser::PushBackToken(t);
status = AssignStmt(in, line);
if(status)
status = Stmt(in, line);
break;
default:
Parser::PushBackToken(t);
return true;
}
return status;
}//End of Stmt
bool SimpleStmt(istream& in, int& line) {
bool status;
LexItem t = Parser::GetNextToken(in, line);
switch( t.GetToken() ) {
case PRINT:
status = PrintStmt(in, line);
if(!status)
{
ParseError(line, "Incorrect Print Statement");
return false;
}
cout << "Print statement in a Simple If statement." << endl;
break;
case IDENT:
Parser::PushBackToken(t);
status = AssignStmt(in, line);
if(!status)
{
ParseError(line, "Incorrect Assignent Statement");
return false;
}
cout << "Assignment statement in a Simple If statement." << endl;
break;
default:
Parser::PushBackToken(t);
return true;
}
return status;
}//End of SimpleStmt
//VarList ::= Var [= Expr] {, Var [= Expr]}
bool VarList(istream& in, int& line) {
bool status = false, exprstatus = false;
string identstr;
LexItem tok = Parser::GetNextToken(in, line);
if(tok == IDENT)
{
identstr = tok.GetLexeme();
if (!(defVar.find(identstr)->second))
{
defVar[identstr] = true;
}
else
{
ParseError(line, "Variable Redefinition");
return false;
}
}
else
{
ParseError(line, "Missing Variable Name");
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok == ASSOP)
{
exprstatus = Expr(in, line);
if(!exprstatus)
{
ParseError(line, "Incorrect initialization for a variable.");
return false;
}
cout<< "Initialization of the variable " << identstr <<" in the declaration statement." << endl;
tok = Parser::GetNextToken(in, line);
if (tok == COMMA) {
status = VarList(in, line);
}
else
{
Parser::PushBackToken(tok);
return true;
}
}
else if (tok == COMMA) {
status = VarList(in, line);
}
else if(tok == ERR)
{
ParseError(line, "Unrecognized Input Pattern");
return false;
}
else {
Parser::PushBackToken(tok);
return true;
}
return status;
}//End of VarList
//PrintStmt:= PRINT *, ExpreList
bool PrintStmt(istream& in, int& line) {
LexItem t;
t = Parser::GetNextToken(in, line);
if( t != DEF ) {
ParseError(line, "Print statement syntax error.");
return false;
}
t = Parser::GetNextToken(in, line);
if( t != COMMA ) {
ParseError(line, "Missing Comma.");
return false;
}
bool ex = ExprList(in, line);
if( !ex ) {
ParseError(line, "Missing expression after Print Statement");
return false;
}
return ex;
}//End of PrintStmt
//BlockIfStmt:= if (Expr) then {Stmt} [Else Stmt]
//SimpleIfStatement := if (Expr) Stmt
bool BlockIfStmt(istream& in, int& line) {
bool ex=false, status ;
static int nestlevel = 0;
int level;
LexItem t;
t = Parser::GetNextToken(in, line);
if( t != LPAREN ) {
ParseError(line, "Missing Left Parenthesis");
return false;
}
ex = RelExpr(in, line);
if( !ex ) {
ParseError(line, "Missing if statement condition");
return false;
}
t = Parser::GetNextToken(in, line);
if(t != RPAREN ) {
ParseError(line, "Missing Right Parenthesis");
return false;
}
t = Parser::GetNextToken(in, line);
if(t != THEN)
{
Parser::PushBackToken(t);
status = SimpleStmt(in, line);
if(status)
{
return true;
}
else
{
ParseError(line, "If-Stmt Syntax Error");
return false;
}
}
nestlevel++;
level = nestlevel;
status = Stmt(in, line);
if(!status)
{
ParseError(line, "Missing Statement for If-Stmt Then-Part");
return false;
}
t = Parser::GetNextToken(in, line);
if( t == ELSE ) {
status = Stmt(in, line);
if(!status)
{
ParseError(line, "Missing Statement for If-Stmt Else-Part");
return false;
}
else
t = Parser::GetNextToken(in, line);
}
if(t != END ) {
ParseError(line, "Missing END of IF");
return false;
}
t = Parser::GetNextToken(in, line);
if(t == IF ) {
cout << "End of Block If statement at nesting level " << level << endl;
return true;
}
Parser::PushBackToken(t);
ParseError(line, "Missing IF at End of IF statement");
return false;
}//End of IfStmt function
//Var:= ident
bool Var(istream& in, int& line)
{
string identstr;
LexItem tok = Parser::GetNextToken(in, line);
if (tok == IDENT){
identstr = tok.GetLexeme();
if (!(defVar.find(identstr)->second))
{
ParseError(line, "Undeclared Variable");
return false;
}
return true;
}
else if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
return false;
}//End of Var
//AssignStmt:= Var = Expr
bool AssignStmt(istream& in, int& line) {
bool varstatus = false, status = false;
LexItem t;
varstatus = Var( in, line);
if (varstatus){
t = Parser::GetNextToken(in, line);
if (t == ASSOP){
status = Expr(in, line);
if(!status) {
ParseError(line, "Missing Expression in Assignment Statment");
return status;
}
}
else if(t.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << t.GetLexeme() << ")" << endl;
return false;
}
else {
ParseError(line, "Missing Assignment Operator");
return false;
}
}
else {
ParseError(line, "Missing Left-Hand Side Variable in Assignment statement");
return false;
}
return status;
}//End of AssignStmt
//ExprList:= Expr {,Expr}
bool ExprList(istream& in, int& line) {
bool status = false;
status = Expr(in, line);
if(!status){
ParseError(line, "Missing Expression");
return false;
}
LexItem tok = Parser::GetNextToken(in, line);
if (tok == COMMA) {
status = ExprList(in, line);
}
else if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
else{
Parser::PushBackToken(tok);
return true;
}
return status;
}//End of ExprList
//RelExpr ::= Expr [ ( == | < | > ) Expr ]
bool RelExpr(istream& in, int& line) {
bool t1 = Expr(in, line);
LexItem tok;
if( !t1 ) {
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
if ( tok == EQ || tok == LTHAN || tok == GTHAN)
{
t1 = Expr(in, line);
if( !t1 )
{
ParseError(line, "Missing operand after operator");
return false;
}
}
return true;
}//End of RelExpr
//Expr ::= MultExpr { ( + | - | // ) MultExpr }
bool Expr(istream& in, int& line) {
bool t1 = MultExpr(in, line);
LexItem tok;
if( !t1 ) {
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
while ( tok == PLUS || tok == MINUS || tok == CAT)
{
t1 = MultExpr(in, line);
if( !t1 )
{
ParseError(line, "Missing operand after operator");
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
}
Parser::PushBackToken(tok);
return true;
}//End of Expr
//MultExpr ::= TermExpr { ( * | / ) TermExpr }
bool MultExpr(istream& in, int& line) {
bool t1 = TermExpr(in, line);
LexItem tok;
if( !t1 ) {
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
while ( tok == MULT || tok == DIV )
{
t1 = TermExpr(in, line);
if( !t1 ) {
ParseError(line, "Missing operand after operator");
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
}
Parser::PushBackToken(tok);
return true;
}//End of MultExpr
//TermExpr ::= SFactor { ** SFactor }
bool TermExpr(istream& in, int& line) {
bool t1 = SFactor(in, line);
LexItem tok;
if( !t1 ) {
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
while ( tok == POW )
{
t1 = SFactor(in, line);
if( !t1 ) {
ParseError(line, "Missing exponent operand");
return false;
}
tok = Parser::GetNextToken(in, line);
if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
}
Parser::PushBackToken(tok);
return true;
}//End of TermExpr
//SFactor = Sign Factor | Factor
bool SFactor(istream& in, int& line)
{
LexItem t = Parser::GetNextToken(in, line);
bool status;
int sign = 0;
if(t == MINUS )
{
sign = -1;
}
else if(t == PLUS)
{
sign = 1;
}
else
Parser::PushBackToken(t);
status = Factor(in, line, sign);
return status;
}//End of SFactor
//Factor := ident | iconst | rconst | sconst | (Expr)
bool Factor(istream& in, int& line, int sign) {
LexItem tok = Parser::GetNextToken(in, line);
//cout << tok.GetLexeme() << endl;
if( tok == IDENT ) {
string lexeme = tok.GetLexeme();
if (!(defVar.find(lexeme)->second))
{
ParseError(line, "Using Undefined Variable");
return false;
}
return true;
}
else if( tok == ICONST ) {
return true;
}
else if( tok == SCONST ) {
return true;
}
else if( tok == RCONST ) {
return true;
}
else if( tok == LPAREN ) {
bool ex = Expr(in, line);
if( !ex ) {
ParseError(line, "Missing expression after (");
return false;
}
if( Parser::GetNextToken(in, line) == RPAREN )
return ex;
else
{
Parser::PushBackToken(tok);
ParseError(line, "Missing ) after expression");
return false;
}
}
else if(tok.GetToken() == ERR){
ParseError(line, "Unrecognized Input Pattern");
cout << "(" << tok.GetLexeme() << ")" << endl;
return false;
}
return false;
}