BTW sorry for the rubbish title :)
On Oct 11, 6:12 pm, matio <[email protected]> wrote:
> 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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