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@@ -363,6 +363,39 @@ $LOAD_PATH << dir unless $LOAD_PATH.include?(dir)
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 #   #main {
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 #     content: string(Hello, "Hubert" Bean.) }
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 #
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+# === Optional Assignment
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+#
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+# You can assign Sass constants if they aren't already assigned
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+# using the ||= assignment operator.
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+# This means that if the constant has already been assigned to,
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+# it won't be re-assigned,
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+# but if it doesn't have a value yet,
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+# it will be given one.
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+# For example:
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+#
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+#   !content = "First content"
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+#   !content ||= "Second content?"
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+#
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+#   #main
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+#     content = content
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+#
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+# is compiled to:
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+#
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+#   #main {
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+#     content: First content; }
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+#
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+# However,
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+#
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+#   !content ||= "Second content?"
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+#
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+#   #main
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+#     content = content
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+#
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+# is compiled to:
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+#
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+#   #main {
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+#     content: Second content?; }
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+#
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 # === Default Concatenation
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 #
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 # All those plusses and quotes for concatenating strings

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@@ -31,7 +31,7 @@ module Sass
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     }
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     # The regular expression used to parse constants
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-    MATCH = /^#{Regexp.escape(CONSTANT_CHAR.chr)}([^\s#{(SYMBOLS.keys + [ ?= ]).map {|c| Regexp.escape("#{c.chr}") }.join}]+)\s*=\s*(.+)/
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+    MATCH = /^#{Regexp.escape(CONSTANT_CHAR.chr)}([^\s#{(SYMBOLS.keys + [ ?= ]).map {|c| Regexp.escape("#{c.chr}") }.join}]+)\s*((?:\|\|)?=)\s*(.+)/
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     # First-order operations
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     FIRST_ORDER = [:times, :div, :mod]

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@@ -270,11 +270,18 @@ module Sass
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     end
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     def parse_constant(line)
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-      name, value = line.scan(Sass::Constant::MATCH)[0]
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+      name, op, value = line.scan(Sass::Constant::MATCH)[0]
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       unless name && value
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         raise SyntaxError.new("Invalid constant: \"#{line}\"", @line)
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       end
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-      @constants[name] = Sass::Constant.parse(value, @constants, @line)
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+
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+      constant = Sass::Constant.parse(value, @constants, @line)
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+      if op == '||='
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+        @constants[name] ||= constant
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+      else
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+        @constants[name] = constant
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+      end
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+
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       :constant
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     end
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@@ -208,6 +208,11 @@ END
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   def test_cr_newline
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     assert_equal("foo {\n  a: b;\n  c: d;\n  e: f; }\n", render("foo\r  a: b\r\n  c: d\n\r  e: f"))
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   end
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+
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+  def test_or_eq
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+    assert_equal("foo {\n  a: b; }\n", render("!foo = b\n!foo ||= c\nfoo\n  a = !foo"))
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+    assert_equal("foo {\n  a: b; }\n", render("!foo ||= b\nfoo\n  a = !foo"))
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+  end
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   private
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