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1 # This file contains definitions of expression grammar
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2
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3 def p_expression_binop(t):
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4 '''expression : expression PLUS expression
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5 | expression MINUS expression
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6 | expression TIMES expression
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7 | expression DIVIDE expression'''
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8 if t[2] == '+' : t[0] = t[1] + t[3]
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9 elif t[2] == '-': t[0] = t[1] - t[3]
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10 elif t[2] == '*': t[0] = t[1] * t[3]
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11 elif t[2] == '/': t[0] = t[1] / t[3]
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12
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13 def p_expression_uminus(t):
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14 'expression : MINUS expression %prec UMINUS'
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15 t[0] = -t[2]
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16
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17 def p_expression_group(t):
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18 'expression : LPAREN expression RPAREN'
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19 t[0] = t[2]
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20
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21 def p_expression_number(t):
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22 'expression : NUMBER'
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23 t[0] = t[1]
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24
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25 def p_expression_name(t):
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26 'expression : NAME'
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27 try:
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28 t[0] = names[t[1]]
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29 except LookupError:
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30 print("Undefined name '%s'" % t[1])
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31 t[0] = 0
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