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diff --git a/lib/rake/doc/rational.rdoc b/lib/rake/doc/rational.rdoc new file mode 100644 index 0000000000..0e1c33873d --- /dev/null +++ b/lib/rake/doc/rational.rdoc @@ -0,0 +1,151 @@ += Why rake? + +Ok, let me state from the beginning that I never intended to write this +code. I'm not convinced it is useful, and I'm not convinced anyone +would even be interested in it. All I can say is that Why's onion truck +must by been passing through the Ohio valley. + +What am I talking about? ... A Ruby version of Make. + +See, I can sense you cringing already, and I agree. The world certainly +doesn't need yet another reworking of the "make" program. I mean, we +already have "ant". Isn't that enough? + +It started yesterday. I was helping a coworker fix a problem in one of +the Makefiles we use in our project. Not a particularly tough problem, +but during the course of the conversation I began lamenting some of the +shortcomings of make. In particular, in one of my makefiles I wanted to +determine the name of a file dynamically and had to resort to some +simple scripting (in Ruby) to make it work. "Wouldn't it be nice if you +could just use Ruby inside a Makefile" I said. + +My coworker (a recent convert to Ruby) agreed, but wondered what it +would look like. So I sketched the following on the whiteboard... + + "What if you could specify the make tasks in Ruby, like this ..." + + task "build" do + java_compile(...args, etc ...) + end + + "The task function would register "build" as a target to be made, + and the block would be the action executed whenever the build + system determined that it was time to do the build target." + +We agreed that would be cool, but writing make from scratch would be WAY +too much work. And that was the end of that! + +... Except I couldn't get the thought out of my head. What exactly +would be needed to make the about syntax work as a make file? Hmmm, you +would need to register the tasks, you need some way of specifying +dependencies between tasks, and some way of kicking off the process. +Hey! What if we did ... and fifteen minutes later I had a working +prototype of Ruby make, complete with dependencies and actions. + +I showed the code to my coworker and we had a good laugh. It was just +about a page worth of code that reproduced an amazing amount of the +functionality of make. We were both truly stunned with the power of +Ruby. + +But it didn't do everything make did. In particular, it didn't have +timestamp based file dependencies (where a file is rebuilt if any of its +prerequisite files have a later timestamp). Obviously THAT would be a +pain to add and so Ruby Make would remain an interesting experiment. + +... Except as I walked back to my desk, I started thinking about what +file based dependencies would really need. Rats! I was hooked again, +and by adding a new class and two new methods, file/timestamp +dependencies were implemented. + +Ok, now I was really hooked. Last night (during CSI!) I massaged the +code and cleaned it up a bit. The result is a bare-bones replacement +for make in exactly 100 lines of code. + +For the curious, you can see it at ... +* doc/proto_rake.rdoc + +Oh, about the name. When I wrote the example Ruby Make task on my +whiteboard, my coworker exclaimed "Oh! I have the perfect name: Rake ... +Get it? Ruby-Make. Rake!" He said he envisioned the tasks as leaves +and Rake would clean them up ... or something like that. Anyways, the +name stuck. + +Some quick examples ... + +A simple task to delete backup files ... + + task :clean do + Dir['*~'].each {|fn| rm fn rescue nil} + end + +Note that task names are symbols (they are slightly easier to type +than quoted strings ... but you may use quoted string if you would +rather). Rake makes the methods of the FileUtils module directly +available, so we take advantage of the <tt>rm</tt> command. Also note +the use of "rescue nil" to trap and ignore errors in the <tt>rm</tt> +command. + +To run it, just type "rake clean". Rake will automatically find a +Rakefile in the current directory (or above!) and will invoke the +targets named on the command line. If there are no targets explicitly +named, rake will invoke the task "default". + +Here's another task with dependencies ... + + task :clobber => [:clean] do + rm_r "tempdir" + end + +Task :clobber depends upon task :clean, so :clean will be run before +:clobber is executed. + +Files are specified by using the "file" command. It is similar to the +task command, except that the task name represents a file, and the task +will be run only if the file doesn't exist, or if its modification time +is earlier than any of its prerequisites. + +Here is a file based dependency that will compile "hello.cc" to +"hello.o". + + file "hello.cc" + file "hello.o" => ["hello.cc"] do |t| + srcfile = t.name.sub(/\.o$/, ".cc") + sh %{g++ #{srcfile} -c -o #{t.name}} + end + +I normally specify file tasks with string (rather than symbols). Some +file names can't be represented by symbols. Plus it makes the +distinction between them more clear to the casual reader. + +Currently writing a task for each and every file in the project would be +tedious at best. I envision a set of libraries to make this job +easier. For instance, perhaps something like this ... + + require 'rake/ctools' + Dir['*.c'].each do |fn| + c_source_file(fn) + end + +where "c_source_file" will create all the tasks need to compile all the +C source files in a directory. Any number of useful libraries could be +created for rake. + +That's it. There's no documentation (other than whats in this +message). Does this sound interesting to anyone? If so, I'll continue +to clean it up and write it up and publish it on RAA. Otherwise, I'll +leave it as an interesting exercise and a tribute to the power of Ruby. + +Why /might/ rake be interesting to Ruby programmers. I don't know, +perhaps ... + +* No weird make syntax (only weird Ruby syntax :-) +* No need to edit or read XML (a la ant) +* Platform independent build scripts. +* Will run anywhere Ruby exists, so no need to have "make" installed. + If you stay away from the "sys" command and use things like + 'ftools', you can have a perfectly platform independent + build script. Also rake is only 100 lines of code, so it can + easily be packaged along with the rest of your code. + +So ... Sorry for the long rambling message. Like I said, I never +intended to write this code at all. |