A recursive descent parser that accepts a source code file as a required command-line argument and displays an appropriate error message if the argument is not provided or the file does not exist. If a user input file contains multiple syntax errors, the program will find and report the first syntax error
Author: Mostofa Adib Shakib
BNF Grammer Rule
P ::= S
S ::= V:=E | read(V) | write(V) | while C do S od | S;S
C ::= E < E | E > E | E = E | E <> E | E <= E | E >= E
E ::= T | E + T | E - T
T ::= F | T * F | T / F
F ::= (E) | N | V
V ::= a | b | … | y | z | aV | bV | … | yV | zV
N ::= 0 | 1 | … | 8 | 9 | 0N | 1N | … | 8N | 9N
Lexeme & Token Pair
| Lexeme | Token |
| --------------- | ------------- |
| := | ASSIGN_OP |
| + | ADD_OP |
| do | KEY_DO |
| < | LESSER_OP |
| - | SUB_OP |
| od | KEY_OD |
| > | GREATER_OP |
| * | MULT_OP |
| variable name | IDENT |
| = | EQUAL_OP |
| / | DIV_OP |
| integer | INT_LIT |
| <> | NEQUAL_OP |
| read | KEY_READ |
| ( | LEFT_PAREN |
| <= | LEQUAL_OP |
| write | KEY_WRITE |
| ) | RIGHT_PAREN |
| >= | GEQUAL_OP |
| while | KEY_WHILE |
| ; | SEMICOLON |