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| function parseProgram() {
program = newProgramASTNode()
advanceTokens()
for (currentToken() != EOF_TOKEN) {
statement = null
if (currentToken() == LET_TOKEN) {
statement = parseLetStatement()
} else if (currentToken() == RETURN_TOKEN) {
statement = parseReturnStatement()
} else if (currentToken() == IF_TOKEN) {
statement = parseIfStatement()
}
if (statement != null) {
program.Statements.push(statement)
}
advanceTokens()
}
return program
}
function parseLetStatement() {
advanceTokens()
identifier = parseIdentifier()
advanceTokens()
if currentToken() != EQUAL_TOKEN {
parseError("no equal sign!")
return null
}
advanceTokens()
value = parseExpression()
variableStatement = newVariableStatementASTNode()
variableStatement.identifier = identifier
variableStatement.value = value
return variableStatement
}
function parseIdentifier() {
identifier = newIdentifierASTNode()
identifier.token = currentToken()
return identifier
}
function parseExpression() {
if (currentToken() == INTEGER_TOKEN) {
if (nextToken() == PLUS_TOKEN) {
return parseOperatorExpression()
} else if (nextToken() == SEMICOLON_TOKEN) {
return parseIntegerLiteral()
}
} else if (currentToken() == LEFT_PAREN) {
return parseGroupedExpression()
}
}
function parseOperatorExpression() {
operatorExpression = newOperatorExpression()
operatorExpression.left = parseIntegerLiteral()
operatorExpression.operator = currentToken()
operatorExpression.right = parseExpression()
return operatorExpression()
}
|
