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