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65 where the three dots stand for arbitrary characters, but not comment delimiters. |
65 where the three dots stand for arbitrary characters, but not comment delimiters. |
66 (Hint: You can assume you are already given a regular expression written \texttt{ALL}, |
66 (Hint: You can assume you are already given a regular expression written \texttt{ALL}, |
67 that can recognise any character, and a regular expression \texttt{NOT} that recognises |
67 that can recognise any character, and a regular expression \texttt{NOT} that recognises |
68 the complement of a regular expression.) |
68 the complement of a regular expression.) |
69 |
69 |
70 |
70 \item How many basic regular expressions are there to match the string |
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71 $abcd$? (ii) How many if they cannot include $\epsilon$ and |
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72 $\varnothing$? (iii) How many if they are also not allowed to |
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73 contain stars? (iv) How many if they are also not allowed to contain |
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74 $\_ + \_$? |
71 |
75 |
72 %\item (Optional) The tokenizer in \texttt{regexp3.scala} takes as |
76 %\item (Optional) The tokenizer in \texttt{regexp3.scala} takes as |
73 %argument a string and a list of rules. The result is a list of tokens. Improve this tokenizer so |
77 %argument a string and a list of rules. The result is a list of tokens. Improve this tokenizer so |
74 %that it filters out all comments and whitespace from the result. |
78 %that it filters out all comments and whitespace from the result. |
75 |
79 |