Change ~ to !.

lib/sass/constant.rb

@@ -30,11 +30,10 @@ module Sass
       ?* => :times,
       ?/ => :div,
       ?% => :mod,
-      ?~ => :not,
       ?& => :single_and,
       ?| => :single_or,
       ?= => :single_equals,
-      CONSTANT_CHAR => :const,
+      CONSTANT_CHAR => :const_or_not,
       STRING_CHAR => :str,
       ESCAPE_CHAR => :esc
     }
@@ -126,7 +125,7 @@ module Sass
               symbol = SYMBOLS[byte]
 
               # Adjacent values without an operator should be concatenated
-              if (symbol.nil? || symbol == :open || symbol == :const) &&
+              if (symbol.nil? || symbol == :open || symbol == :const_or_not) &&
                   last && (!last.is_a?(Symbol) || last == :close)
                 to_return << :concat
               end
@@ -138,7 +137,7 @@ module Sass
               end
 
               # Time for a unary op!
-              if ![nil, :open, :close, :const, :single_and, :single_or, :single_equals].include?(symbol) && beginning_of_token
+              if ![nil, :open, :close, :const_or_not, :single_and, :single_or, :single_equals].include?(symbol) && beginning_of_token
                 beginning_of_token = true
                 to_return << :unary << symbol
                 next
@@ -149,8 +148,9 @@ module Sass
                 next
               end
 
-              if symbol == :single_equals && last == :not
+              if symbol == :single_equals && last == :const_or_not
                 to_return[-1] = :not_equals
+                to_return.slice!(-2) if to_return[-2] == :concat
                 next
               end
 
@@ -185,12 +185,10 @@ module Sass
             to_return << parenthesize(value)
           when :unary
             to_return << [value.shift, parenthesize(value, true)]
-          when :const
+          when :const_or_not
             raise Sass::SyntaxError.new("Unterminated constant.") if value.first.nil?
-            raise Sass::SyntaxError.new("Invalid constant.") unless value.first.is_a?(::String)
 
-            to_return << [:const, value.first]
-            value.shift
+            to_return << (value.first.is_a?(::String) ? [:const, value.shift] : [:not, parenthesize(value, true)])
           else
             to_return << token
           end

test/sass/engine_test.rb

@@ -46,7 +46,6 @@ class SassEngineTest < Test::Unit::TestCase
     "@import templates/basic\n  foo" => "Illegal nesting: Nothing may be nested beneath import directives.",
     "foo\n  @import templates/basic" => "Import directives may only be used at the root of a document.",
     "!foo = bar baz !" => "Unterminated constant.",
-    "!foo = !(foo)" => "Invalid constant.",
     "=foo\n  :color red\n.bar\n  +bang" => "Undefined mixin 'bang'.",
     ".bar\n  =foo\n    :color red\n" => ["Mixins may only be defined at the root of a document.", 2],
     "=foo\n  :color red\n.bar\n  +foo\n    :color red" => "Illegal nesting: Nothing may be nested beneath mixin directives.",
@@ -404,8 +403,8 @@ a {
 CSS
 !var = true
 a
-  b = ~~!var
-  c = ~!var
+  b = !!!var
+  c = !!var
 SASS
   end
 
@@ -429,7 +428,7 @@ SASS
 a
   @if !var
     b: 1
-  @if ~!var
+  @if !!var
     b: 2
 SASS
   end
@@ -447,10 +446,10 @@ CSS
 a
   t1 = "foo" == foo
   t2 = 1 == 1.0
-  t3 = false ~= true
+  t3 = false != true
   f1 = foo == bar
   f2 = 1em == 1px
-  f3 = 12 ~= 12
+  f3 = 12 != 12
 SASS
   end
 
@@ -509,7 +508,7 @@ a-1 {
   blooble: gloop; }
 CSS
 !a = 5
-@while !a ~= 0
+@while !a != 0
   a-\#{!a}
     blooble: gloop
   !a = !a - 1