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parser.cpp
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parser.cpp
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#include "parser.h"
QList<Token *> scan(const QString &code) {
QList<Token *> tokenList;
for (auto it = code.cbegin(); it != code.cend(); ++it) {
if (it->isSpace()) { continue; }
if (!tokenList.isEmpty() && tokenList.back()->type == TOKEN_KEYWORD &&
((KeywordToken *)tokenList.back())->value == KEYWORD_REM) {
tokenList.append(new StringToken(code.mid(it - code.cbegin()).trimmed()));
return tokenList;
} else if (it->isLetter() || *it == '_') {
QString value{ *it };
while (it + 1 != code.cend() && ((it + 1)->isLetterOrNumber() || *(it + 1) == '_')) {
value.append(*(++it));
}
if (value == keywordString[KEYWORD_REM]) {
tokenList.append(new KeywordToken(KEYWORD_REM));
} else if (value == keywordString[KEYWORD_LET]) {
tokenList.append(new KeywordToken(KEYWORD_LET));
} else if (value == keywordString[KEYWORD_PRINT]) {
tokenList.append(new KeywordToken(KEYWORD_PRINT));
} else if (value == keywordString[KEYWORD_INPUT]) {
tokenList.append(new KeywordToken(KEYWORD_INPUT));
} else if (value == keywordString[KEYWORD_GOTO]) {
tokenList.append(new KeywordToken(KEYWORD_GOTO));
} else if (value == keywordString[KEYWORD_IF]) {
tokenList.append(new KeywordToken(KEYWORD_IF));
} else if (value == keywordString[KEYWORD_THEN]) {
tokenList.append(new KeywordToken(KEYWORD_THEN));
} else if (value == keywordString[KEYWORD_END]) {
tokenList.append(new KeywordToken(KEYWORD_END));
} else if (value == keywordString[KEYWORD_MOD]) {
tokenList.append(new OperatorToken(MOD));
} else { tokenList.append(new IdentifierToken(value)); }
} else if (it->isDigit()) {
qint64 value = it->digitValue();
while (it + 1 != code.cend() && (it + 1)->isDigit()) {
value = value * 10 + (++it)->digitValue();
}
tokenList.append(new ConstantToken(value));
} else if (*it == '+') {
if (!tokenList.isEmpty() && (
tokenList.back()->type == TOKEN_CONSTANT ||
tokenList.back()->type == TOKEN_IDENTIFIER ||(
tokenList.back()->type == TOKEN_OPERATOR &&
((OperatorToken *)tokenList.back())->value == RIGHT_PAREN))) {
tokenList.append(new OperatorToken(PLUS));
} else { tokenList.append(new OperatorToken(POSITIVE)); }
} else if (*it == '-') {
if (!tokenList.isEmpty() && (
tokenList.back()->type == TOKEN_CONSTANT ||
tokenList.back()->type == TOKEN_IDENTIFIER || (
tokenList.back()->type == TOKEN_OPERATOR &&
((OperatorToken *)tokenList.back())->value == RIGHT_PAREN))) {
tokenList.append(new OperatorToken(MINUS));
} else { tokenList.append(new OperatorToken(NEGATIVE)); }
} else if (*it == '*') {
if (it + 1 != code.cend() && *(it + 1) == '*') {
tokenList.append(new OperatorToken(POWER));
++it;
} else { tokenList.append(new OperatorToken(TIMES)); }
} else if (*it == '/') {
tokenList.append(new OperatorToken(OVER));
} else if (*it == '<') {
if (it + 1 != code.cend() && *(it + 1) == '=') {
tokenList.append(new OperatorToken(LESS_EQUAL));
++it;
} else if (it + 1 != code.cend() && *(it + 1) == '>') {
tokenList.append(new OperatorToken(NOT_EQUAL));
++it;
} else { tokenList.append(new OperatorToken(LESS)); }
} else if (*it == '>') {
if (it + 1 != code.cend() && *(it + 1) == '=') {
tokenList.append(new OperatorToken(GREATER_EQUAL));
++it;
} else { tokenList.append(new OperatorToken(GREATER)); }
} else if (*it == '=') {
tokenList.append(new OperatorToken(EQUAL));
} else if (*it == '(') {
tokenList.append(new OperatorToken(LEFT_PAREN));
} else if (*it == ')') {
tokenList.append(new OperatorToken(RIGHT_PAREN));
} else {
tokenList.append(new StringToken(code.mid(it - code.cbegin()).trimmed()));
throw QPair<QList<Token *>, ScanError>(tokenList, "illegal character.");
}
}
return tokenList;
}
Expression *parserExpression(const QList<Token *> &tokenList) {
QStack<OperatorType> operatorStack;
QStack<Expression *> expressionStack;
#define MAKE_EXPRESSION(op) \
while (!operatorStack.empty() && operatorStack.top() < op) { \
if (operatorStack.top() == POSITIVE || operatorStack.top() == NEGATIVE) { \
if (expressionStack.empty()) { \
throw ParserError("missing operand of operator \"" + operatorString[operatorStack.top()] + "\"."); \
} \
expressionStack.push(new UnaryOperatorExpression(operatorStack.pop(), expressionStack.pop())); \
} else { \
if (expressionStack.size() < 2) { \
throw ParserError("missing operand of operator \"" + operatorString[operatorStack.top()] + "\"."); \
} \
Expression *right = expressionStack.pop(); \
expressionStack.push(new BinaryOperatorExpression(operatorStack.pop(), expressionStack.pop(), right)); \
} \
}
for (auto it = tokenList.cbegin(); it != tokenList.cend(); ++it) {
switch ((*it)->type) {
case TOKEN_IDENTIFIER:
expressionStack.push(new VariableExpression(((IdentifierToken *)*it)->value));
break;
case TOKEN_CONSTANT:
expressionStack.push(new NumberExpression(((ConstantToken *)*it)->value));
break;
case TOKEN_OPERATOR:
switch (((OperatorToken *)*it)->value) {
case TIMES:
case OVER:
case MOD:
MAKE_EXPRESSION(PLUS);
break;
case PLUS:
case MINUS:
MAKE_EXPRESSION(LESS);
break;
case LESS:
case LESS_EQUAL:
case GREATER_EQUAL:
case GREATER:
MAKE_EXPRESSION(EQUAL);
break;
case EQUAL:
case NOT_EQUAL:
MAKE_EXPRESSION(LEFT_PAREN);
break;
case RIGHT_PAREN:
MAKE_EXPRESSION(LEFT_PAREN);
}
if (((OperatorToken *)*it)->value == RIGHT_PAREN) {
if (operatorStack.empty()) { throw ParserError("missing left paren."); }
operatorStack.pop();
} else { operatorStack.push(((OperatorToken *)*it)->value); }
break;
default:
throw ParserError("excess statement after expression.");
}
}
MAKE_EXPRESSION(LEFT_PAREN);
if (!operatorStack.empty()) { throw ParserError("missing right paren."); }
if (expressionStack.empty()) { throw ParserError("empty expression."); }
if (expressionStack.size() > 1) { throw ParserError("illegal expression."); }
return expressionStack.top();
#undef MAKE_EXPRESSION
}
Statement *parser(const QList<Token *> &tokenList) {
if (tokenList.isEmpty()) { return nullptr; }
auto it = tokenList.cbegin();
if ((*it)->type != TOKEN_KEYWORD) { throw ParserError("illegal statement."); }
switch (((KeywordToken *)*it)->value) {
case KEYWORD_REM:
return new RemStatement(++it == tokenList.cend() ? "" : ((StringToken *)*it)->value);
case KEYWORD_LET: {
if (++it == tokenList.cend()) { throw ParserError("missing variable name and assignment."); }
if ((*it)->type != TOKEN_IDENTIFIER) { throw ParserError("illegal variable name."); }
QString variable = ((IdentifierToken *)*it)->value;
if (++it == tokenList.cend() ||
(*it)->type != TOKEN_OPERATOR ||
((OperatorToken *)*it)->value != EQUAL) {
throw ParserError("missing assignment operator after variable name.");
}
Expression *expression;
try { expression = parserExpression(tokenList.mid(++it - tokenList.cbegin())); }
catch (ParserError error) { throw error; }
return new LetStatement(variable, expression);
}
case KEYWORD_PRINT: {
Expression *expression;
try { expression = parserExpression(tokenList.mid(++it - tokenList.cbegin())); }
catch (ParserError error) { throw error; }
return new PrintStatement(expression);
}
case KEYWORD_INPUT: {
if (++it == tokenList.cend()) { throw ParserError("missing variable name."); }
if ((*it)->type != TOKEN_IDENTIFIER) { throw ParserError("illegal variable name."); }
if (it + 1 != tokenList.cend()) { throw ParserError("excess statement after variable name."); }
return new InputStatement(((IdentifierToken *)*it)->value);
}
case KEYWORD_GOTO: {
if (++it == tokenList.cend()) { throw ParserError("missing destination."); }
if ((*it)->type != TOKEN_CONSTANT) { throw ParserError("destination must be constant."); };
if (it + 1 != tokenList.cend()) { throw ParserError("excess statement after destination."); }
return new GotoStatement(((ConstantToken *)*it)->value);
}
case KEYWORD_IF: {
decltype(it) it0 = ++it;
while (++it != tokenList.cend() && (
(*it)->type != TOKEN_KEYWORD ||
((KeywordToken *)*it)->value != KEYWORD_THEN));
if (it == tokenList.cend()) { throw ParserError("missing THEN in IF statement."); }
Expression *condition;
try { condition = parserExpression(tokenList.mid(it0 - tokenList.cbegin(), it - it0)); }
catch (ParserError error) { throw error; }
if (++it == tokenList.cend()) { throw ParserError("missing destination."); }
if ((*it)->type != TOKEN_CONSTANT) { throw ParserError("destination must be constant."); }
if (it + 1 != tokenList.cend()) { throw ParserError("excess statement after destination."); }
return new IfStatement(condition, ((ConstantToken *)*it)->value);
}
case KEYWORD_END:
if (it + 1 != tokenList.cend()) { throw ParserError("excess statement after END"); }
return new EndStatement();
}
}