80 lines
1.5 KiB
Python
80 lines
1.5 KiB
Python
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#!/usr/bin/env python
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TS_A = 'a'
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TS_B = 'b'
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TS_PLUS = '+'
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TS_MULT = '*'
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SYM_END = object()
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NTS_E = 1
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NTS_T = 2
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NTS_F = 3
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# 1. E -> E + T
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# 2. E -> T
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# 3. T -> T * F
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# 4. T -> F
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# 5. F -> 'a'
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# 1. E -> T F
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# 2. F -> '+' T F
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# 3. F ->
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# 4. T -> 'b'
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# 5. T -> 'a'
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table = {
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NTS_E : {
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TS_A: 1,
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TS_B: 1,
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},
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NTS_F : {
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TS_PLUS: 2,
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SYM_END: 3
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},
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NTS_T : {
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TS_A: 4,
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TS_B: 5
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}
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}
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def tparse(text):
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stack = []
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stack.append(NTS_E);
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while len(stack) > 0:
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if len(text) == 0:
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c = SYM_END
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else:
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c = text[0]
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if c == stack[-1]:
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text = text[1:]
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stack.pop()
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else:
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try:
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rule = table[stack[-1]][c]
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except KeyError:
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print("Unexpected %s" % c)
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return
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if rule == 1:
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stack.pop()
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stack.append(NTS_F)
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stack.append(NTS_T)
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elif rule == 2:
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stack.pop()
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stack.append(NTS_F)
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stack.append(NTS_T)
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stack.append(TS_PLUS)
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elif rule == 3:
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stack.pop()
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elif rule == 4:
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stack.pop()
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stack.append(TS_A)
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elif rule == 5:
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stack.pop()
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stack.append(TS_B)
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else:
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print("Unexpected %s" % (text[0]))
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return
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print("Applied rule %d" % rule)
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if __name__ == '__main__':
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tparse("b+a+b+b+a")
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