1 # ----------------------------------------------------------------------------- 2 # yacc_literal.py 3 # 4 # Grammar with bad literal characters 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','+','-'), 16 ('left','*','/'), 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_expr(t): 28 'statement : expression' 29 print(t[1]) 30 31 def p_expression_binop(t): 32 '''expression : expression '+' expression 33 | expression '-' expression 34 | expression '*' expression 35 | expression '/' expression 36 | expression '**' expression ''' 37 if t[2] == '+' : t[0] = t[1] + t[3] 38 elif t[2] == '-': t[0] = t[1] - t[3] 39 elif t[2] == '*': t[0] = t[1] * t[3] 40 elif t[2] == '/': t[0] = t[1] / t[3] 41 42 def p_expression_uminus(t): 43 'expression : MINUS expression %prec UMINUS' 44 t[0] = -t[2] 45 46 def p_expression_group(t): 47 'expression : LPAREN expression RPAREN' 48 t[0] = t[2] 49 50 def p_expression_number(t): 51 'expression : NUMBER' 52 t[0] = t[1] 53 54 def p_expression_name(t): 55 'expression : NAME' 56 try: 57 t[0] = names[t[1]] 58 except LookupError: 59 print("Undefined name '%s'" % t[1]) 60 t[0] = 0 61 62 def p_error(t): 63 print("Syntax error at '%s'" % t.value) 64 65 yacc.yacc() 66 67 68 69 70
