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