symbols

Bang dollar seems to refer to the last part of the last command line. E.g. $ ls -l .... something $ !$ -l bash: -l command not found I can find plenty on the dollar variables (e.g. $! ) but not on this. Any explanation? That's the last argument of the previous command. From the documentation : !!:$ designates the last argument of the preceding command. This may be shortened to !$ . Remark. If you want to play around with Bash's history, I suggest you turn on the shell option histverify like so: shopt -s histverify (you can also put it in your .bashrc to have it on permanently). When using

This question already has an answer here: What is the “equals greater than” operator => in Ruby? 1 answer While learning Ruby I've come across the "=>" operator on occasion. Usually I see it in the form of :symbol => value and it seems to be used frequently when passing values to functions. What exactly is that operator called? What does it do/mean? Is it built into Ruby or is it something that different frameworks like Rails and DataMapper add to the symbol class? Is it only used in conjunction with the symbol class? Thanks. => separates the keys from the values in a hashmap literal. It is

I'm new to Haskell and, in general, to functional programming, and I'm a bit uncomfortable with its syntax. In the following code what does the => denote? And also (Num a, Ord a) ? loop :: (Num a, Ord a) => a -> (t -> t) -> t -> t This is a typeclass constraint; (Num a, Ord a) => ... means that loop works with any type a that is an instance of the Num and Ord typeclasses, corresponding to numeric types and ordered types respectively. Basically, you can think of loop as having the type on the right hand side of the => , except that a is required to be an instance of Num and Ord . You can think

I'm trying to program a graph class using an adjacent list from an example in my C++ text book, and when I compile using this command: Code: g++ -o prog program.cpp ...I get the following error: Undefined symbols for architecture x86_64: "_main", referenced from: start in crt1.10.6.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status ... what in the world does this mean? It may turn out to be an issue with my code, but I feel like it may be deeper than that, because I've gotten this same seemingly inexplicable error for several different projects, many of which

I've read a few instances in reading mathematics and computer science that use the equivalence symbol ≡ , (basically an '=' with three lines) and it always makes sense to me to read this as if it were equality. What is the difference between these two concepts? Eugene Yokota Wikipedia: Equivalence relation : In mathematics, an equivalence relation is a binary relation between two elements of a set which groups them together as being "equivalent" in some way. Let a, b, and c be arbitrary elements of some set X. Then "a ~ b" or "a ≡ b" denotes that a is equivalent to b. An equivalence relation "

How should I encode special characters into web pages? For instance I need this symbol ℃, which I used just by copying and pasting the character as I can see it now. This worked for the desktop browsers I checked with and also on iPad and iPhone but nothing is displayed on a Blackberry I used for testing. Is there a standard best practice for this? http://www.fileformat.info/info/unicode/char/2103/browsertest.htm Nix Try to replace it with ° , and also to set the charset to utf-8, as Martin suggests. °C will get you something like this: If you really want to use the DEGREE CELSIUS character “℃

I like this literal expression for an array of strings: %w( i can easily create arrays of words ) I am wondering if there is a literal to get an array of symbols. I know I can do %w( it is less elegant to create arrays of symbols ).map( &:to_sym ) but it would be so wonderful just to use a literal. David Grayson Yes! This is possible now in Ruby 2.0.0. One way to write it is: %i{foo bar} # => [:foo, :bar] You can also use other delimiters, so you could also write %i(foo bar) or %i!foo bar! for example. This feature was originally announced here: http://www.ruby-lang.org/zh_TW/news/2012/11/02