ruby ÒªÈçºÎ寫bnf

ÎÒÊÇÓÃnetbeans È¥寫bnf

a program will ONLY accept strings based on the following grammar:

            <compute> --> <value> = <expression>

            <value> --> X | Y | Z

            <expression> --> <value> + <expression>

                                                | <value> - <expression>

                                                | <value>

ÎÒÓÃÒÑ經ÓÃtreetop È¥寫rules


ÎÒ現ÔÚ×öµ½output and input




ÎÒ現ÔÚÒªÖªµÀÔõ麼check letter
ÏñÊÇËûÈç¹ûÊÇС寫µÄ話¾ÍÊÇ Lexical Error: Unrecognized character ¡®z¡¯
Èç¹ûÊÀx y z ÒÔÍâµÄ話 ¾ÍÊÇSyntax Error: Operation ¡®a b¡¯ is invalid


還ÓÐÔõ麼show bnf ÔÚÄã°´enter時  Ëû會°ÑËùÓеÄshow ³ö來

ÏòÊÇ X=X+Y-Z

<compute> --> <value> = <expression>