I would like to step through Ruby code at runtime, but it seems difficult to find a decent Ruby IDE for OS X which allows you to do this. I would prefer one which uses the native look and feel of the OS (Cocoa).
Can anyone make a suggestion?
The main feature I am looking for is the ability to step through the code, not really much else. I have TextMate for editing.
Personally I use TextMate which is amazing however heard good things about RubyMine from JetBrains - www.jetbrains.com/ruby/index.html
Aptana RadRails is a free one, based on eclipse does regular ruby too. you wont get the osx ui, but it will work. It's not too bad either.
You might want to try Komodo Edit, which is more in line with TextMate than say a full blown IDE like Aptana RadRails. It lacks things like debugging or interactive shells, but you can run scripts from within the editor and it has all the code auto-completing features that you'd expect from an IDE. And it looks very pretty and it's FREE. =)
It seems many text editors for OSX play well with Ruby and in some instances, like TextMate, were built for Ruby.
But if you're shopping for an IDE, check out Netbeans. Its Ruby support is fantastic. Lot's of nice little features that'll make you appreciate it.
As for stepping through code:
Single-step or run through Ruby code and ERB files. Set breakpoints, look at local variables, navigate the call stack, switch threads. Hover the mouse over a variable in the Editor to evaluate the expressions and show it in a tooltip. The NetBeans IDE supports the Fast Ruby Debugger, which also works with JRuby. You can even attach the debugger to any remote process started from the command line, and get all the advantages of a user-friendly debugger fronten
I would recommend TextMate as above and also MacVim if possible. Sometimes the simplicity of a good text editor is better than an IDE.