Functinal Style Ruby

After playing with Ruby for weeks, I found Ruby is yet interesting. I try to write my code a bit in the likeness of Erlang, where symbol vs atom, array vs list. And the most important syntax that I like are:

• everything return a value
• may return multiple values
• begin-end clause is lambda that may be directly applied
• parallel assignment

Now, let's write some code before and after (functional):

Example1:

Before

   1. cond = {}  
   2. if par[:id]  
   3.   feed = Feed.find(par[:id])  
   4.   if feed  
   5.     cond[:feed] = feed.id  
   6.   end  
   7. end  
   8. if par[:m]
   9.   limit = par[:m].to_i  
  10. else  
  11.   limit = 20  
  12. end  
  13. if limit >= 4096  
  14.   limit = 4096  
  15. end  
  16. cond[:limit] = limit  
  17. if par[:d]  
  18.   days = par[:d].to_f  
  19.   if days <= 0 || days >= 365  
  20.     days = 365  
  21.   end  
  22.   cond[:time] = Time.now - days*86400  
  23. end  

After

   1. cond = {  
   2.   :feed   => if par[:id]  
   3.                feed = Feed.find(par[:id])  
   4.                feed ? feed.id : nil  
   5.              end,  
   6.   :limit  => begin  
   7.                 limit = par[:m] ? par[:m].to_i : 20  
   8.                 limit >= 4096 ? 4096 : limit  
   9.              end,  
  10.   :time   => if par[:d]  
  11.                days = par[:d].to_f  
  12.                days = days <= 0 || days >= 365 ? 365 : days  
  13.                Time.now - days * 86400  
  14.              end,  
  15. }.delete_if { |k, v| v.nil? } # delete all nil elements of cond  

Example2:

Before

   1.  if f[:mode] == "rss"  
   2.   rss = f[:feed]  
   3.   params[:feed][:channel] = rss.channel.title  
   4.   params[:feed][:description] = rss.channel.description  
   5.   params[:feed][:link] = rss.channel.link  
   6.   params[:feed][:copyright] = rss.channel.copyright  
   7. else  
   8.   atom = f[:feed]  
   9.   params[:feed][:channel] = atom.title  
  10.   params[:feed][:description] = atom.subtitle  
  11.   params[:feed][:link] = atom.links.join  
  12.   params[:feed][:copyright] = atom.rights  
  13. end  

After

   1. params[:feed][:channel],    
   2. params[:feed][:description],    
   3. params[:feed][:link],    
   4. params[:feed][:copyright] = if f[:mode] == "rss"    
   5.                               rss = f[:feed]   
   6.   
   7.                               [rss.channel.title,    
   8.                                rss.channel.description,    
   9.                                rss.channel.link,    
  10.                                rss.channel.copyright]  
  11.                             else    
  12.                               atom = f[:feed]  
  13.     
  14.                               [atom.title,    
  15.                                atom.subtitle,    
  16.                                atom.links.join,    
  17.                                atom.rights]    
  18.                             end    

Example3

   1. # grp_str: p -> public(0) , u -> user(1), f -> friends(2)   
   2. def privilege_cond(user, grp_str)  
   3.   grp_str ||= 'puf'  
   4.   cond = {:pre => "", :sub => []}  
   5.   cond = if loggedin?(user)  
   6.            frds = grp_str.include?('f') ? user.friends.find(:all) : []  
   7.            frd_ids = frds.collect { |frd| frd.friend_id.to_i }  
   8.              
   9.            cond = if grp_str.include?('u')  
  10.                     {:pre => cond[:pre] + (cond[:pre] == "" ? "" : "OR") +   
  11.                              " user_id  = ? ",  
  12.                      :sub => cond[:sub] + [user.id]}  
  13.                   else  
  14.                     cond  
  15.                   end  
  16.       
  17.            cond = if grp_str.include?('f') && !frd_ids.empty?  
  18.                     {:pre => cond[:pre] + (cond[:pre] == "" ? "" : "OR") +   
  19.                              " user_id in (?) AND privilege in (?) ",  
  20.                      :sub => cond[:sub] + [frd_ids, [0, 2]]}  
  21.                   else  
  22.                     cond  
  23.                   end  
  24.       
  25.            cond = if grp_str.include?('p')  
  26.                     {:pre => cond[:pre] + (cond[:pre] == "" ? "" : "OR") +   
  27.                              " user_id != ? AND privilege  = ? ",  
  28.                      :sub => cond[:sub] + [user.id, 0]}  
  29.                   else  
  30.                      cond  
  31.                   end  
  32.          else  
  33.            {:pre => "privilege = ?",  
  34.             :sub => [0]}  
  35.          end  
  36. end