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Hi, I'm working on a define a new language with lex and yacc. However, lexer works fine but yacc doesn't. I'm not pretty sure if my grammar is completely right. I get "syntax error in input" from yacc.


My lexing.py:

# lexer.input(data). Reset the lexer and store a new input string.
# lexer.token(). Return the next token. Returns a special LexToken instance on success or None if the end of the input text has been reached.
# lexer = lex.lex()


import lex

# List of token names.   This is always required
tokens = (
    'NUMBER',
    'RED',
    'GREEN',
    'BLUE',
    'BLACK',
    'FORW',
    'RIGHT',
    'LOOP',
    'COLOR',
    'PEN',
    'LSQB',
    'RSQB',
    'EMPTY'
    
)
 
# Regular expression rules for simple tokens
t_FORW    = r'F'
t_RIGHT   = r'R'
t_LOOP   = r'L'
t_COLOR  = r'COLOR'
t_PEN  = r'PEN'
t_LSQB  = r'\['
t_RSQB  = r'\]'
t_RED  = r'K'
t_GREEN  = r'Y'
t_BLUE  = r'M'
t_BLACK  = r'S'
t_EMPTY = r'\ '


 
# A regular expression rule with some action code
def t_NUMBER(t):
    r'\d+'
    t.value = int(t.value)    
    return t
 
# Define a rule so we can track line numbers
def t_newline(t):
    r'\n+'
    t.lexer.lineno += len(t.value)
 
# A string containing ignored characters (spaces and tabs)
t_ignore  = ' \t'
 
# Error handling rule
def t_error(t):
    print("Illegal character '%s'" % t.value[0])
    t.lexer.skip(1)
 
# Build the lexer
lexer = lex.lex()

# Test it out
data = '''F 100 90'''
 
# Give the lexer some input
lexer.input(data)

# Tokenize 
for tok in lexer:
    print(tok)



########################################
#PARSER
'''
statement : forward | right | loop 
forward : option F num statement | option F num 
option : color | pen | empty
right : R num statement | R num
loop : L num [ statement ]
color : Color clrs
clrs : m | k | s | y
pen: Pen num
'''


What I have tried:

import yacc
from lexing import data, tokens


def p_root(p):
    """root : function NUMBER option
             | COLOR colors option
            | PEN NUMBER option """


def p_option(p):
    """option : root
               | LSQB root RSQB root
               | EMPTY """


def p_function(p):
    """function : FORW
                | RIGHT
                | LOOP """


def p_colors(p):
    """colors : RED
              | BLUE
              | GREEN
              | BLACK """


def p_error(p):
    print("Syntax error in input!")


# Build the parser
parser = yacc.yacc()
result = parser.parse(data)
# print (result)
Posted
Updated 19-May-22 23:54pm
v2

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