From: John Carter <john.carter@...>
Date: 2008-04-30T07:01:30+09:00
Subject: Small tweak to ruby lexing to create optimal aspects / DbC / 	debugtraces.

On Wed, 30 Apr 2008, Joel VanderWerf wrote:

> You can put debug code (invariant checks, and puts), flush with the left 
> margin (unindented). Then these lines can be grepped for with ^\w, more or 
> less. They also stand out when you scan the code visually.

Hokay, now that's an idea! But lets generalize it a little....

What if we added a switch to ruby...

ruby -A regexp -R replacementString filename.rb

Which would have the meaning that all occurences of #regexp in the
code get replaced by replacementString. Where the default
replacementString is empty.

So for example, if you had ruby code "myfile.rb" like so...

def myfunc(a)
     #PRECOND raise "Bad a" unless someexpression(a)

     do_stuff

     #DEBUG_LOG "a=#{a}, b=#{b}"

     do_otherstuff

     #POSTCOND raise "Didn't work" unless otherexpression
end

Then running it with an old version of ruby, or with the new version
the code would just work, the #PREBLAH would be treated as comments at
lex time and discarded.

def myfunc(a)
     do_stuff
     do_otherstuff
end

The code would run optimally fast.

Not run it with....

ruby -A PRECOND myfile.rb

The lexer would replace "#PRECOND" with "", and the parser would see
it and evaluated it, leaving the POSTCOND commented out.

def myfunc(a)
     raise "Bad a" unless someexpression(a)

     do_stuff

     do_otherstuff

end

It gets even better...

ruby -A "(PRE|POST)COND" -R "check_invariant;" myfile.rb

and the parser sees a full Design by Contract checking

def myfunc(a)
     check_invariant;raise "Bad a" unless someexpression(a)

     do_stuff

     do_otherstuff

     check_invariant; raise "Didn't work" unless otherexpression
end

Or if you just want a debug logging trace...

ruby -A DEBUG_LOG -R "puts"  myfile.rb
   or
ruby -A DEBUG_LOG -R "STDERR.puts"  myfile.rb
   or
ruby -A DEBUG_LOG -R "$log_file.puts" -e '$log_file=open("logfile.txt","w")' myfile.rb

Of course one can just create a wrapper on ruby that accepts any
options, but grabs the -A and -R options if present and any file
names, does a search and replace on the file "filename.rb", writing
the result to a temporary file "_aspect_filename.rb" and then invoking
ruby with the rest of the parameters on "_aspect_filename.rb".


The problem with that is the search and replace is just done on the
top level file, not on any files loaded or required.

Another problem is that a lot of care would have to be taken not to
get confused by # characters in all the many varieties of strings,
heredocs, regexps and character literals.

Hmm. Possibly one can search and replace loads and requires to do the
same. Hmm.

Anyway, any suggestions before I try a write the proof of concept
wrapper and then maybe make it an RCR?





John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand