Thanks, when this:
# calc.py
#
# A simple calculator with variables. This is from O'Reilly's
# "Lex and Yacc", p. 63.
#
import sys
sys.path.insert(0,"../..")
if sys.version_info[0] >= 3:
raw_input = input
reserved = {
'string':'STRDEF'
}
tokens = [
'NUMBER','STRING', 'NAME'
] + list(reserved.values())
literals = ['=','+','-','*','%','/', '(',')']
# Tokens
t_STRING = r'"[a-zA-Z0-9]*"'
#t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
def t_NUMBER(t):
r'\d+'
t.value = int(t.value)
return t
def t_NAME(t):
r'[a-zA-Z_][a-zA-Z0-9_]*'
t.value = reserved.get(t.value, 'NAME')
return t
t_ignore = " \t"
def t_newline(t):
r'\n+'
t.lexer.lineno += t.value.count("\n")
def t_error(t):
print("Illegal character '%s'" % t.value[0])
t.lexer.skip(1)
# Build the lexer
import ply.lex as lex
lex.lex()
# Parsing rules
precedence = (
('left','+','-'),
('left','*','/'),
('right','UMINUS'),
)
# dictionary of names
names = { }
def p_statement_assign(p):
'''statement : STRDEF NAME "=" STRING
| NAME "=" expression'''
if p[2] == "=": names[p[1]] = p[3]
if p[3] == "=": names[p[2]] = p[4]
def p_statement_expr(p):
'statement : expression'
print(p[1])
def p_expression_binop(p):
'''expression : expression '+' expression
| expression '-' expression
| expression '*' expression
| expression '/' expression
| expression '%' expression'''
if p[2] == '+' : p[0] = p[1] + p[3]
elif p[2] == '-': p[0] = p[1] - p[3]
elif p[2] == '*': p[0] = p[1] * p[3]
elif p[2] == '/': p[0] = p[1] / p[3]
elif p[2] == '%': p[0] = p[1] % p[3]
def p_expression_uminus(p):
"expression : '-' expression %prec UMINUS"
p[0] = -p[2]
def p_expression_group(p):
"expression : '(' expression ')'"
p[0] = p[2]
def p_expression_number(p):
"expression : NUMBER"
p[0] = p[1]
def p_expression_name(p):
"expression : NAME"
try:
p[0] = names[p[1]]
except LookupError:
print("Undefined name '%s'" % p[1])
p[0] = 0
def p_error(p):
if p:
print("Syntax error at '%s'" % p.value)
else:
print("Syntax error at EOF")
import ply.yacc as yacc
yacc.yacc()
while 1:
try:
s = raw_input('calc > ')
except EOFError:
break
if not s: continue
yacc.parse(s)
is run it says:
Syntax error at 'NAME'
On Oct 11, 6:09 pm, David Beazley <[email protected]> wrote:
> ID is the default token type to use if get() can't find the name in
> the dictionary. In your case, it would be 'NAME'.
>
> -Dave
>
> On Oct 11, 2009, at 12:02 PM, matio wrote:
>
>
>
> > "t.type = reserved.get(t.value,'ID')"
> > what is the 'ID' bit?
> > Thanks for the help
>
> > On Oct 11, 2:11 pm, David Beazley <[email protected]> wrote:
> >> On Oct 11, 2009, at 7:55 AM, Bruce Frederiksen wrote:
>
> >>> I'm going to go with specifying t_STRING after t_NAME, so that the
> >>> word "string" is taken as a NAME. Try putting t_STRING before
> >>> t_NAME...
>
> >> [snip]
>
> >>> # Tokens
>
> >>> t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
> >>> t_STRING = r'"[a-zA-Z0-9]*"'
> >>> t_STRDEF = 'string'
>
> >> I'm going to agree with this. The t_STRDEF token is being matched by
> >> the t_NAME rule above it which is almost certainly causing this
> >> problem. The original poster should look
> >> athttp://www.dabeaz.com/ply/ply.html#ply_nn6
> >> and note the part about "reserved words."
>
> >> This problem comes up so often, I'm almost wondering if I should add
> >> an extra validation check to PLY. It occurs to me that I could
> >> modify lex to look for regexes that are made up of nothing but simple
> >> characters (e.g., 'string' above) and then test them for matches
> >> against the other regular expressions (e.g., t_NAME). If a match is
> >> found, some kind of stern warning message could be issued about it.
>
> >> As the documentation states, it's really a bad idea to make separate
> >> token rules for reserved words like 'string', 'if', 'else', etc.
>
> >> Cheers,
> >> Dave
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