1 # ----------------------------------------------------------------------------- 2 # yacc_badprec.py 3 # 4 # Bad precedence specifier 5 # ----------------------------------------------------------------------------- 6 import sys 7 8 if ".." not in sys.path: sys.path.insert(0,"..") 9 import ply.yacc as yacc 10 11 from calclex import tokens 12 13 # Parsing rules 14 precedence = "blah" 15 16 # dictionary of names 17 names = { } 18 19 def p_statement_assign(t): 20 'statement : NAME EQUALS expression' 21 names[t[1]] = t[3] 22 23 def p_statement_expr(t): 24 'statement : expression' 25 print(t[1]) 26 27 def p_expression_binop(t): 28 '''expression : expression PLUS expression 29 | expression MINUS expression 30 | expression TIMES expression 31 | expression DIVIDE expression''' 32 if t[2] == '+' : t[0] = t[1] + t[3] 33 elif 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 37 def p_expression_uminus(t): 38 'expression : MINUS expression %prec UMINUS' 39 t[0] = -t[2] 40 41 def p_expression_group(t): 42 'expression : LPAREN expression RPAREN' 43 t[0] = t[2] 44 45 def p_expression_number(t): 46 'expression : NUMBER' 47 t[0] = t[1] 48 49 def p_expression_name(t): 50 'expression : NAME' 51 try: 52 t[0] = names[t[1]] 53 except LookupError: 54 print("Undefined name '%s'" % t[1]) 55 t[0] = 0 56 57 def p_error(t): 58 print("Syntax error at '%s'" % t.value) 59 60 yacc.yacc() 61 62 63 64 65
