yacc_badprec2.py (1496B)
1# ----------------------------------------------------------------------------- 2# yacc_badprec2.py 3# 4# Bad precedence 5# ----------------------------------------------------------------------------- 6import sys 7sys.tracebacklimit = 0 8 9sys.path.insert(0,"..") 10import ply.yacc as yacc 11 12from calclex import tokens 13 14# Parsing rules 15precedence = ( 16 42, 17 ('left','TIMES','DIVIDE'), 18 ('right','UMINUS'), 19 ) 20 21# dictionary of names 22names = { } 23 24def p_statement_assign(t): 25 'statement : NAME EQUALS expression' 26 names[t[1]] = t[3] 27 28def p_statement_expr(t): 29 'statement : expression' 30 print t[1] 31 32def p_expression_binop(t): 33 '''expression : expression PLUS expression 34 | expression MINUS expression 35 | expression TIMES expression 36 | expression DIVIDE 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[3] == '/': t[0] = t[1] / t[3] 41 42def p_expression_uminus(t): 43 'expression : MINUS expression %prec UMINUS' 44 t[0] = -t[2] 45 46def p_expression_group(t): 47 'expression : LPAREN expression RPAREN' 48 t[0] = t[2] 49 50def p_expression_number(t): 51 'expression : NUMBER' 52 t[0] = t[1] 53 54def 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 62def p_error(t): 63 print "Syntax error at '%s'" % t.value 64 65yacc.yacc() 66 67 68 69