Answers to Part 4 Exercises

	Answers to Part 4 Exercises

	Solution to k37 Problem

	% substitute /$.$k37$.k37$/\1q53\2

	will do it. When there are two or more wild cards in a search
	pattern, the editor finds the longest match for the first one that
	allows any match for the subsequent ones, and so on.


	Solution to Capitalization Problem

	237 , 289 substitute :[^ ]*:\L\u&:g

	Since the "\u" and "\l" metacharacters have limited reach, they
	don't end the effect of a "\L" or "\U" metacharacter--they only
	make a one-character exception.

	Author's Note: Since I wrote this solution, I have learned that
	it will not work under many implementations of the editor. So,
	I've added below an alternate solution, more complex but more
	powerful, that should work everywhere.

	237 , 289 substitute :$[A-Za-z]$$[A-Za-z-]*$:\u\1\L\2:g

	Even in editing environments where my first solution would work,
	the second one has certain advantages:

	The second solution is not fooled by situations where
	a punctuation mark leads off a word.

	It's up to you whether the second solution does or does not
	capitalize any but the first word in hyphenated compounds such
	as Frankfurt-am-Main. If you want to capitalize those subsequent
	words, just remove the last of the three hyphens within the
	second character class in my alternate solution.


	Answer to No-Op Problem


	The editor thinks a substitution has been successfully made
	whenever the outgoing search pattern is matched and no error
	condition is encountered, even if it is only replacing nothing
	with nothing. So when the editor finishes up by reporting the
	number of substitutions it has made, it is giving me a count of
	the empty lines in my file, which tells me how many paragraphs
	plus headlines plus list items I have. Then I divide this number
	into the count of lines in the file, to see whether my
	paragraphs have gotten too long.


	Solution to HTML tags problem

	Where the substitution command to add a tag at the start of
	a paragraph presently removes and then replaces any first
	character on the line, now it should remove and replace anything
	except a "<" character in that position. If that first
	character is a "<" it is necessary that the substitution command
	fail so it will change nothing. To arrange this, replace that
	period in the search pattern with a negative character class --
	"[^<]" -- which matches any character except the one that begins
	every HTML tag.

	Similarly, replace the period in the other substitution pattern
	with the negative character class that matches any character
	except the one that always ends an HTML tag. Now the two
	commands will look like this:

	global /^$/ + substitute /^[^<]/<P>&/
	global /^$/ - substitute :[^>]$:&</P>:


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	Answers to Part 4 Exercises

	Solution to k37 Problem

	% substitute /\(.\)k37\(.k37\)/\1q53\2

	will do it. When there are two or more wild cards in a search
	pattern, the editor finds the longest match for the first one that
	allows any match for the subsequent ones, and so on.


	Solution to Capitalization Problem

	237 , 289 substitute :[^ ]*:\L\u&:g

	Since the "\u" and "\l" metacharacters have limited reach, they
	don't end the effect of a "\L" or "\U" metacharacter--they only
	make a one-character exception.

	Author's Note: Since I wrote this solution, I have learned that
	it will not work under many implementations of the editor. So,
	I've added below an alternate solution, more complex but more
	powerful, that should work everywhere.

	237 , 289 substitute :\([A-Za-z]\)\([A-Za-z-]*\):\u\1\L\2:g

	Even in editing environments where my first solution would work,
	the second one has certain advantages:

	The second solution is not fooled by situations where
	a punctuation mark leads off a word.

	It's up to you whether the second solution does or does not
	capitalize any but the first word in hyphenated compounds such
	as Frankfurt-am-Main. If you want to capitalize those subsequent
	words, just remove the last of the three hyphens within the
	second character class in my alternate solution.


	Answer to No-Op Problem


	The editor thinks a substitution has been successfully made
	whenever the outgoing search pattern is matched and no error
	condition is encountered, even if it is only replacing nothing
	with nothing. So when the editor finishes up by reporting the
	number of substitutions it has made, it is giving me a count of
	the empty lines in my file, which tells me how many paragraphs
	plus headlines plus list items I have. Then I divide this number
	into the count of lines in the file, to see whether my
	paragraphs have gotten too long.


	Solution to HTML tags problem

	Where the substitution command to add a tag at the start of
	a paragraph presently removes and then replaces any first
	character on the line, now it should remove and replace anything
	except a "<" character in that position. If that first
	character is a "<" it is necessary that the substitution command
	fail so it will change nothing. To arrange this, replace that
	period in the search pattern with a negative character class --
	"[^<]" -- which matches any character except the one that begins
	every HTML tag.

	Similarly, replace the period in the other substitution pattern
	with the negative character class that matches any character
	except the one that always ends an HTML tag. Now the two
	commands will look like this:

	global /^$/ + substitute /^[^<]/<P>&/
	global /^$/ - substitute :[^>]$:&</P>:


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