1 # ----------------------------------------------------------------------------- 2 # yacc_rr.py 3 # 4 # A grammar with a reduce/reduce conflict 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 = ( 15 ('left','PLUS','MINUS'), 16 ('left','TIMES','DIVIDE'), 17 ('right','UMINUS'), 18 ) 19 20 # dictionary of names 21 names = { } 22 23 def p_statement_assign(t): 24 'statement : NAME EQUALS expression' 25 names[t[1]] = t[3] 26 27 def p_statement_assign_2(t): 28 'statement : NAME EQUALS NUMBER' 29 names[t[1]] = t[3] 30 31 def p_statement_expr(t): 32 'statement : expression' 33 print(t[1]) 34 35 def p_expression_binop(t): 36 '''expression : expression PLUS expression 37 | expression MINUS expression 38 | expression TIMES expression 39 | expression DIVIDE expression''' 40 if t[2] == '+' : t[0] = t[1] + t[3] 41 elif t[2] == '-': t[0] = t[1] - t[3] 42 elif t[2] == '*': t[0] = t[1] * t[3] 43 elif t[2] == '/': t[0] = t[1] / t[3] 44 45 def p_expression_uminus(t): 46 'expression : MINUS expression %prec UMINUS' 47 t[0] = -t[2] 48 49 def p_expression_group(t): 50 'expression : LPAREN expression RPAREN' 51 t[0] = t[2] 52 53 def p_expression_number(t): 54 'expression : NUMBER' 55 t[0] = t[1] 56 57 def p_expression_name(t): 58 'expression : NAME' 59 try: 60 t[0] = names[t[1]] 61 except LookupError: 62 print("Undefined name '%s'" % t[1]) 63 t[0] = 0 64 65 def p_error(t): 66 print("Syntax error at '%s'" % t.value) 67 68 yacc.yacc() 69 70 71 72 73
