presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/getDateTimeFunctionType
class AstBuilder:    private static CurrentTime.Function getDateTimeFunctionType(Token token)
    {
        switch (token.getType()) {
            case SqlBaseLexer.CURRENT_DATE:
                return CurrentTime.Function.DATE;
            case SqlBaseLexer.CURRENT_TIME:
                return CurrentTime.Function.TIME;
            case SqlBaseLexer.CURRENT_TIMESTAMP:
                return CurrentTime.Function.TIMESTAMP;
            case SqlBaseLexer.LOCALTIME:
                return CurrentTime.Function.LOCALTIME;
            case SqlBaseLexer.LOCALTIMESTAMP:
                return CurrentTime.Function.LOCALTIMESTAMP;
        }

        throw new IllegalArgumentException("Unsupported special function: " + token.getText());
    }