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parser.cpp
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parser.cpp
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#include "parser.h"
#include "token.h"
#include "ast.h"
Parser::Parser(const std::string& file) : lex(file) {
}
Expression* Parser::Term() {
Expression *left = Factor(), *right;
TokenId op_id = lex.PeekToken().Id;
while (op_id == PLUS || op_id == MINUS) {
lex.NextToken();
right = Factor();
BinaryOperator *temp = new BinaryOperator(left, right, op_id);
left = temp;
op_id = lex.PeekToken().Id;
}
return left;
}
Expression* Parser::Factor() {
Expression *left = Primary(), *right;
TokenId op_id = lex.PeekToken().Id;
while (op_id == MULT || op_id == DIV) {
lex.NextToken();
right = Primary();
BinaryOperator *temp = new BinaryOperator(left, right, op_id);
left = temp;
op_id = lex.PeekToken().Id;
}
return left;
}
Expression* Parser::Primary() {
Expression *expr = NULL;
if (lex.PeekToken().Id == NUMBER) {
expr = new Constant(lex.NextToken());
} else if (lex.PeekToken().Id == MINUS) {
lex.NextToken();
expr = new UnaryOperator(Primary(), MINUS);
} else if (lex.PeekToken().Id == LPAREN) {
lex.NextToken();
expr = Term();
lex.NextToken();
}
return expr;
}