brew deps foo bar now gives the dependency intersection

Rationale: this is more useful than the union, and you can still easily get the union by running the command twice and concatenating the result.

Library/Homebrew/cmd/deps.rb

@@ -1,14 +1,24 @@
+require 'formula'
+
 module Homebrew extend self
   def deps
-    puts if ARGV.include?('--all')
-      require 'formula'
-      Formula.all.each do |f|
-        "#{f.name}:#{f.deps.join(' ')}"
+    if ARGV.include? '--all'
+      Formula.each do |f|
+        # TODO add a space after the colon??
+        puts "#{f.name}:#{f.deps*' '}"
       end
-    elsif ARGV.include?("-1") or ARGV.include?("--1")
-      *ARGV.formulae.map{ |f| f.deps or [] }.flatten.uniq.sort
     else
-      *ARGV.formulae.map{ |f| f.recursive_deps.map{ |f| f.name } }.flatten.uniq.sort
+      func = if ARGV.one? then :deps else :recursive_deps end
+      puts ARGV.formulae.map(&func).intersection.sort
     end
   end
 end
+
+class Array
+  def intersection
+    a = []
+    each{ |b| a |= b }
+    each{ |c| a &= c }
+    a
+  end
+end

Library/Homebrew/extend/ARGV.rb

@@ -54,6 +54,9 @@ module HomebrewArgvExtension
   def build_head?
     flag? '--HEAD'
   end
+  def one?
+    flag? "--1"
+  end
 
   def flag? flag
     options_only.each do |arg|