yacc_notok.py revision 2632:1bb2f91485ea
1# ----------------------------------------------------------------------------- 2# yacc_notok.py 3# 4# A grammar, but we forgot to import the tokens list 5# ----------------------------------------------------------------------------- 6 7import sys 8sys.tracebacklimit = 0 9 10# Parsing rules 11precedence = ( 12 ('left','PLUS','MINUS'), 13 ('left','TIMES','DIVIDE'), 14 ('right','UMINUS'), 15 ) 16 17# dictionary of names 18names = { } 19 20def p_statement_assign(t): 21 'statement : NAME EQUALS expression' 22 names[t[1]] = t[3] 23 24def p_statement_expr(t): 25 'statement : expression' 26 print t[1] 27 28def p_expression_binop(t): 29 '''expression : expression PLUS expression 30 | expression MINUS expression 31 | expression TIMES expression 32 | expression DIVIDE expression''' 33 if t[2] == '+' : t[0] = t[1] + t[3] 34 elif t[2] == '-': t[0] = t[1] - t[3] 35 elif t[2] == '*': t[0] = t[1] * t[3] 36 elif t[3] == '/': t[0] = t[1] / t[3] 37 38def p_expression_uminus(t): 39 'expression : MINUS expression %prec UMINUS' 40 t[0] = -t[2] 41 42def p_expression_group(t): 43 'expression : LPAREN expression RPAREN' 44 t[0] = t[2] 45 46def p_expression_number(t): 47 'expression : NUMBER' 48 t[0] = t[1] 49 50def p_expression_name(t): 51 'expression : NAME' 52 try: 53 t[0] = names[t[1]] 54 except LookupError: 55 print "Undefined name '%s'" % t[1] 56 t[0] = 0 57 58def p_error(t): 59 print "Syntax error at '%s'" % t.value 60 61import yacc 62yacc.yacc() 63 64 65 66 67