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1 # -----------------------------------------------------------------------------
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2 # yacc_uprec2.py
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3 #
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4 # A grammar with a bad %prec specifier
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5 # -----------------------------------------------------------------------------
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6 import sys
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7
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8 if ".." not in sys.path: sys.path.insert(0,"..")
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9 import ply.yacc as yacc
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10
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11 from calclex import tokens
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12
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13 # Parsing rules
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14
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15 # dictionary of names
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16 names = { }
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17
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18 def p_statement_assign(t):
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19 'statement : NAME EQUALS expression'
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20 names[t[1]] = t[3]
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21
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22 def p_statement_expr(t):
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23 'statement : expression'
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24 print(t[1])
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25
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26 def p_expression_binop(t):
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27 '''expression : expression PLUS expression
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28 | expression MINUS expression
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29 | expression TIMES expression
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30 | expression DIVIDE expression'''
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31 if t[2] == '+' : t[0] = t[1] + t[3]
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32 elif t[2] == '-': t[0] = t[1] - t[3]
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33 elif t[2] == '*': t[0] = t[1] * t[3]
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34 elif t[2] == '/': t[0] = t[1] / t[3]
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35
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36 def p_expression_uminus(t):
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37 'expression : MINUS expression %prec'
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38 t[0] = -t[2]
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39
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40 def p_expression_group(t):
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41 'expression : LPAREN expression RPAREN'
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42 t[0] = t[2]
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43
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44 def p_expression_number(t):
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45 'expression : NUMBER'
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46 t[0] = t[1]
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47
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48 def p_expression_name(t):
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49 'expression : NAME'
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50 try:
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51 t[0] = names[t[1]]
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52 except LookupError:
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53 print("Undefined name '%s'" % t[1])
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54 t[0] = 0
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55
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56 def p_error(t):
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57 print("Syntax error at '%s'" % t.value)
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58
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59 yacc.yacc()
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60
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61
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62
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63
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