73 lines
1.6 KiB
Python
73 lines
1.6 KiB
Python
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# -----------------------------------------------------------------------------
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# yacc_unused_rule.py
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#
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# Grammar with an unused rule
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# -----------------------------------------------------------------------------
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import sys
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if ".." not in sys.path: sys.path.insert(0,"..")
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import ply.yacc as yacc
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from calclex import tokens
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# Parsing rules
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precedence = (
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('left','PLUS','MINUS'),
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('left','TIMES','DIVIDE'),
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('right','UMINUS'),
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)
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# dictionary of names
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names = { }
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def p_statement_assign(t):
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'statement : NAME EQUALS expression'
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names[t[1]] = t[3]
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def p_statement_expr(t):
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'statement : expression'
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print(t[1])
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def p_expression_binop(t):
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'''expression : expression PLUS expression
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| expression MINUS expression
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| expression TIMES expression
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| expression DIVIDE expression'''
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if t[2] == '+' : t[0] = t[1] + t[3]
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elif t[2] == '-': t[0] = t[1] - t[3]
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elif t[2] == '*': t[0] = t[1] * t[3]
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elif t[2] == '/': t[0] = t[1] / t[3]
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def p_expression_uminus(t):
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'expression : MINUS expression %prec UMINUS'
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t[0] = -t[2]
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def p_expression_group(t):
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'expression : LPAREN expression RPAREN'
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t[0] = t[2]
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def p_expression_number(t):
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'expression : NUMBER'
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t[0] = t[1]
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def p_expression_name(t):
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'expression : NAME'
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try:
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t[0] = names[t[1]]
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except LookupError:
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print("Undefined name '%s'" % t[1])
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t[0] = 0
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def p_integer(t):
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'integer : NUMBER'
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t[0] = t[1]
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def p_error(t):
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print("Syntax error at '%s'" % t.value)
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yacc.yacc()
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