Don't install dependencies that are already installed

Library/Homebrew/brew.h.rb

@@ -155,7 +155,7 @@ def expand_deps fae
       f.deps.each do |name|
         f = Formula.factory name
         deps << expand_deps(f) if f.deps # hideous inefficient
-        deps << f
+        deps << f unless f.installed?
       end
     when Hash
       # TODO implement optional and recommended
@@ -166,6 +166,7 @@ def expand_deps fae
     end
     deps << f
   end
+
   # TODO much more efficient to use a set and not recurse stuff already done
   return deps.flatten.uniq
 end

bin/brew

@@ -91,12 +91,12 @@ begin
         end
       end
 
+      unless ARGV.force?
         unless system "which #{ENV['CC'] or 'cc'} &> /dev/null" and $?.success?
           raise "We cannot find a c compiler, have you installed the latest Xcode?"
         end
-
         fae = ARGV.formulae.reject do |f|
-        if f.installed? and not ARGV.force?
+          if f.installed?
             message = "Formula already installed: #{f.prefix}"
             if ARGV.formulae.count > 1
               opoo message
@@ -106,8 +106,13 @@ begin
             true
           end
         end
+        exit 0 if fae.empty?
+      else
+        fae=ARGV.formulae
+      end
 
-      fae=expand_deps ARGV.formulae
+      # the resulting order will be optimal for super-deps and deps
+      fae=expand_deps fae
 
       require 'beer_events'