» CS 330 Lecture 7 – Regex: Replacement with Blocks

CS 330 Lecture 7 – Regex: Replacement with Blocks

February 8, 2016 by Chris Johnson. Filed under cs330, lectures, spring 2016.

Agenda

what ?s
program this
gsub examples
- src2html
- eval’ing embedded math
regex bingo

TODO

Right now:

You and a partner make a 4×4 grid of randomly generated strings. Include upper- and lowercase letters, numbers, whitespace, and punctuation. Keep the strings short. There’s no free space.

Before Wednesday:

Familiarize yourself with grammars and ANTLR. Read Grammar: The Language of Languages. On a 1/4 sheet, write a little grammar to match boolean expressions comprised of boolean literals, variable identifiers, binary operators || and &&, and unary operator !. Allow for parentheses to elevate the enclosed operation’s precedence: !(true || isTall).

Note

Let’s start with a Program This, excerpted from Advent of Code:

Santa needs help figuring out which strings in his text file are naughty or nice.

A nice string is one with all of the following properties:

It contains at least three vowels (aeiou only), like aei, xazegov, or aeiouaeiouaeiou.

It contains at least one letter that appears twice in a row, like xx, abcdde (dd), or aabbccdd (aa, bb, cc, or dd).

It does not contain the strings ab, cd, pq, or xy, even if they are part of one of the other requirements.

With a partner, write a write Ruby expression that evaluates true if a string is nice.

Today we close out our focus on regular expressions with a few more examples, hitting upon the ideas of greedy vs. lazy and replacing the matching text with the result of some code using a block.

Code

advent.rb

/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `'

eval_report.rb

/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `'