diff --git a/crocgrammar.txt b/crocgrammar.txt
index 5153310..2fb084f 100644
--- a/crocgrammar.txt
+++ b/crocgrammar.txt
@@ -249,7 +249,6 @@ ReturnTypes:
 
 Type:
 	BasicType
-	! null
 	not null
 	any
 	@ DottedName
@@ -425,7 +424,6 @@ EqualExpression:
 	ShiftExpression == ShiftExpression
 	ShiftExpression != ShiftExpression
 	ShiftExpression is ShiftExpression
-	ShiftExpression ! is ShiftExpression
 	ShiftExpression is not ShiftExpression
 
 RelExpression:
@@ -435,7 +433,6 @@ RelExpression:
 	ShiftExpression >= ShiftExpression
 	ShiftExpression <=> ShiftExpression
 	ShiftExpression in ShiftExpression
-	ShiftExpression ! in ShiftExpression
 	ShiftExpression not in ShiftExpression
 
 ShiftExpression:
diff --git a/samples/threadtest.croc b/samples/threadtest.croc
index 495ae82..2fafbb0 100644
--- a/samples/threadtest.croc
+++ b/samples/threadtest.croc
@@ -63,7 +63,7 @@ class Thread
 	{
 		if(:mNeedMessage)
 		{
-			assert(:mMessageHead !is null)
+			assert(:mMessageHead is not null)
 			:mNeedMessage = false
 			local ok, value = :receive()
 			assert(ok)
diff --git a/src/croc/compiler/parser.cpp b/src/croc/compiler/parser.cpp
index 003eb60..75959ec 100644
--- a/src/croc/compiler/parser.cpp
+++ b/src/croc/compiler/parser.cpp
@@ -688,7 +688,7 @@ namespace croc
 
 				ret = cast(uint32_t)TypeMask::Any;
 			}
-			else if(l.type() == Token::Not || l.type() == Token::NotKeyword)
+			else if(l.type() == Token::NotKeyword)
 			{
 				l.next();
 				l.expect(Token::Null);
@@ -1901,25 +1901,6 @@ namespace croc
 				exp1 = new(c) NotEqualExp(location, exp2->endLocation, exp1, exp2);
 				break;
 
-			case Token::Not:
-				if(l.peek().type == Token::Is)
-				{
-					l.next();
-					l.next();
-					exp2 = parseShiftExp();
-					exp1 = new(c) NotIsExp(location, exp2->endLocation, exp1, exp2);
-				}
-				else if(l.peek().type == Token::In)
-				{
-					l.next();
-					l.next();
-					exp2 = parseShiftExp();
-					exp1 = new(c) NotInExp(location, exp2->endLocation, exp1, exp2);
-				}
-				// no, there should not be an 'else' here
-
-				break;
-
 			case Token::NotKeyword:
 				if(l.peek().type == Token::In)
 				{
diff --git a/src/croc/stdlib/docs.croc b/src/croc/stdlib/docs.croc
index 3dd0b05..7c3f475 100644
--- a/src/croc/stdlib/docs.croc
+++ b/src/croc/stdlib/docs.croc
@@ -126,7 +126,7 @@ access their doc tables through their parents' \tt{children} doctable member. Th
 */
 function childDocs(obj: class|namespace, child: string)
 {
-	if(child !in obj)
+	if(child not in obj)
 		throw ValueError("Object has no child named '{}'".format(child))
 
 	local docs = docsOf(obj)
diff --git a/src/croc/stdlib/doctools_console.croc b/src/croc/stdlib/doctools_console.croc
index 00868b8..d9389bf 100644
--- a/src/croc/stdlib/doctools_console.croc
+++ b/src/croc/stdlib/doctools_console.croc
@@ -227,7 +227,7 @@ class BasicConsoleOutputter : DocOutputter
 	{
 		:beginParagraph()
 
-		if(name !is "docs")
+		if(name is not "docs")
 		{
 			:beginBold()
 
@@ -494,7 +494,7 @@ class BasicConsoleOutputter : DocOutputter
 
 				local first, second = splitAtWS(s, remaining)
 
-				if(first !is null)
+				if(first is not null)
 					:baseWrite(first)
 
 				:newline()
diff --git a/src/croc/stdlib/doctools_output.croc b/src/croc/stdlib/doctools_output.croc
index e7bca31..b491b99 100644
--- a/src/croc/stdlib/doctools_output.croc
+++ b/src/croc/stdlib/doctools_output.croc
@@ -64,7 +64,7 @@ class LinkResolver
 		// Might be some globals added by user code that aren't in docsOf(_G).children
 		foreach(name, val; _G)
 		{
-			if(name !is "_G" && name !in :_globals && name !in modules.loaded)
+			if(name is not "_G" && name not in :_globals && name not in modules.loaded)
 			{
 				if(local dt = docsOf(val))
 					:_globals[name] = :_makeMapRec(dt)
@@ -99,7 +99,7 @@ class LinkResolver
 	*/
 	function enterModule(name: string)
 	{
-		if(:_item !is null || :_module !is null)
+		if(:_item is not null || :_module is not null)
 			throw StateError("Attempting to enter a module from {} scope".format(:currentScope()))
 
 		if(local m = :_modules[name])
@@ -117,7 +117,7 @@ class LinkResolver
 	*/
 	function enterItem(name: string)
 	{
-		if(:_item !is null || :_module is null)
+		if(:_item is not null || :_module is null)
 			throw StateError("Attempting to enter an item from {} scope".format(:currentScope()))
 
 		if(local i = :_module.children[name])
@@ -133,9 +133,9 @@ class LinkResolver
 	*/
 	function leave()
 	{
-		if(:_item !is null)
+		if(:_item is not null)
 			:_item = null
-		else if(:_module !is null)
+		else if(:_module is not null)
 			:_module = null
 		else
 			throw StateError("Attempting to leave at global scope")
@@ -196,10 +196,10 @@ class LinkResolver
 	// Private
 
 	function _inItem(link: string) =
-		:_item !is null && link in :_item.children
+		:_item is not null && link in :_item.children
 
 	function _inCurModule(link: string) =
-		:_module !is null && :_inModule(:_module, link)
+		:_module is not null && :_inModule(:_module, link)
 
 	function _inModules(link: string)
 	{
@@ -262,7 +262,7 @@ class LinkResolver
 		local f = link[dot + 1 ..]
 		local i = :_globals[n]
 
-		return i !is null && i.children && f in i.children
+		return i is not null && i.children && f in i.children
 	}
 
 	function _inGlobals(link: string) =
@@ -376,7 +376,7 @@ class LinkTranslator
 
 /// Checks if a given name is a valid name for a doc section.
 function validSectionName(name: string) =
-	!(#name == 0 || (#name == 1 && name[0] == '_') || (name[0] != '_' && name !in stdSections))
+	!(#name == 0 || (#name == 1 && name[0] == '_') || (name[0] != '_' && name not in stdSections))
 
 /// Checks if a paragraph list is empty (has no actual text).
 function isPlistEmpty(plist: array) =
@@ -502,7 +502,7 @@ function toHeader(doctable: table, parentFQN: string, full: bool = true)
 
 			if(doctable.name == "constructor")
 			{
-				if(parentFQN !is "")
+				if(parentFQN is not "")
 					ret.append(parentFQN, ".")
 
 				ret.append("this")
@@ -512,7 +512,7 @@ function toHeader(doctable: table, parentFQN: string, full: bool = true)
 				if(full)
 					ret.append("function ")
 
-				if(parentFQN !is "")
+				if(parentFQN is not "")
 					ret.append(parentFQN, ".")
 
 				ret.append(doctable.name)
@@ -544,7 +544,7 @@ function toHeader(doctable: table, parentFQN: string, full: bool = true)
 			if(full)
 				ret.append(doctable.kind, " ")
 
-			if(parentFQN !is "")
+			if(parentFQN is not "")
 				ret.append(parentFQN, ".")
 
 			ret.append(doctable.name)
@@ -557,7 +557,7 @@ function toHeader(doctable: table, parentFQN: string, full: bool = true)
 			break
 
 		case "field":
-			if(parentFQN !is "")
+			if(parentFQN is not "")
 				ret.append(parentFQN, ".")
 
 			ret.append(doctable.name)
@@ -573,7 +573,7 @@ function toHeader(doctable: table, parentFQN: string, full: bool = true)
 			if(full)
 				ret.append(doctable.protection, " ")
 
-			if(parentFQN !is "")
+			if(parentFQN is not "")
 				ret.append(parentFQN, ".")
 
 			ret.append(doctable.name)
@@ -706,7 +706,7 @@ class SectionOrder
 
 		// Make sure all standard sections are accounted for
 		foreach(sec; stdSections)
-			if(sec !in order)
+			if(sec not in order)
 				throw ValueError("Standard section '{}' does not exist in the given order".format(sec))
 
 		// Make sure there are no duplicates
@@ -749,7 +749,7 @@ class SectionOrder
 			throw ValueError("Invalid section name '{}'".format(target))
 		else if(sec == target)
 			throw ValueError("Section names must be different")
-		else if(target !in ord)
+		else if(target not in ord)
 			throw ValueError("Section '{}' does not exist in the section order".format(target))
 
 		local ord = :_sectionOrder
diff --git a/src/croc/stdlib/doctools_trac.croc b/src/croc/stdlib/doctools_trac.croc
index 176b5bd..9263509 100644
--- a/src/croc/stdlib/doctools_trac.croc
+++ b/src/croc/stdlib/doctools_trac.croc
@@ -146,7 +146,7 @@ class TracWikiOutputter : DocOutputter
 
 	override function beginSection(name: string)
 	{
-		if(name !is "docs")
+		if(name is not "docs")
 		{
 			:beginParagraph()
 			:beginBold()
diff --git a/src/croc/stdlib/hash_weaktables.croc b/src/croc/stdlib/hash_weaktables.croc
index 7f0c306..08a3645 100644
--- a/src/croc/stdlib/hash_weaktables.croc
+++ b/src/croc/stdlib/hash_weaktables.croc
@@ -74,7 +74,7 @@ class WeakKeyTable : WeakTableBase
 			{
 				local v = :_data[keys[idx]]
 
-				if(v !is null)
+				if(v is not null)
 					return deref(keys[idx]), v
 			}
 		}
@@ -107,7 +107,7 @@ class WeakKeyTable : WeakTableBase
 	/**
 	Gets an array of the keys (dereferenced) of this table.
 	*/
-	function keys() = [deref(k) foreach k, _; :_data if deref(k) !is null]
+	function keys() = [deref(k) foreach k, _; :_data if deref(k) is not null]
 
 	/**
 	Gets an array of the values of this table.
@@ -171,7 +171,7 @@ class WeakValTable : WeakTableBase
 			{
 				local v = deref(:_data[keys[idx]])
 
-				if(v !is null)
+				if(v is not null)
 					return keys[idx], v
 			}
 		}
@@ -209,7 +209,7 @@ class WeakValTable : WeakTableBase
 	/**
 	Gets an array of the values (dereferenced) of this table.
 	*/
-	function values() = [deref(v) foreach _, v; :_data if deref(v) !is null]
+	function values() = [deref(v) foreach _, v; :_data if deref(v) is not null]
 
 	/**
 	Normalizes the table by removing any key-value pairs where the value has been collected. This is usually called
@@ -266,7 +266,7 @@ class WeakKeyValTable : WeakTableBase
 			{
 				local v = deref(:_data[keys[idx]])
 
-				if(v !is null)
+				if(v is not null)
 					return deref(keys[idx]), v
 			}
 		}
@@ -299,12 +299,12 @@ class WeakKeyValTable : WeakTableBase
 	/**
 	Gets an array of the keys (dereferenced) of this table.
 	*/
-	function keys() = [deref(k) foreach k, _; :_data if deref(k) !is null]
+	function keys() = [deref(k) foreach k, _; :_data if deref(k) is not null]
 
 	/**
 	Gets an array of the values (dereferenced) of this table.
 	*/
-	function values() = [deref(v) foreach _, v; :_data if deref(v) !is null]
+	function values() = [deref(v) foreach _, v; :_data if deref(v) is not null]
 
 	/**
 	Normalizes the table by removing any key-value pairs where the key or value have been collected. This is usually
diff --git a/src/croc/stdlib/serialization.croc b/src/croc/stdlib/serialization.croc
index 4742f98..36438d3 100644
--- a/src/croc/stdlib/serialization.croc
+++ b/src/croc/stdlib/serialization.croc
@@ -128,7 +128,7 @@ local class Serializer
 		}
 
 		local method = SerializeMethods[typeof(val)]
-		assert(method !is null, "t: " ~ typeof(val))
+		assert(method is not null, "t: " ~ typeof(val))
 		return :(method)(val)
 	}
 
@@ -508,7 +508,7 @@ local class Deserializer
 				throw ValueError("Malformed data (expected object of type '{}' but found '{}' instead)".format(r))
 		}
 
-		if(typeof(val) !is w)
+		if(typeof(val) is not w)
 		{
 			throw ValueError("Malformed data (expected type '{}' but found a backref to type '{}' instead)".format(
 				w, niceTypeof(val)))
diff --git a/src/croc/stdlib/stream.croc b/src/croc/stdlib/stream.croc
index a96c833..5e35037 100644
--- a/src/croc/stdlib/stream.croc
+++ b/src/croc/stdlib/stream.croc
@@ -1047,7 +1047,7 @@ class TextReader
 
 		#:_chunks = 0
 
-		while outer(:_string !is "")
+		while outer(:_string is not "")
 		{
 			foreach(pos, c; :_string)
 			{
@@ -1294,7 +1294,7 @@ class NativeStream : Stream
 	*/
 	override this(stream: nativeobj, caps: string)
 	{
-		if(hidden(with this, "handle") !is null)
+		if(hidden(with this, "handle") is not null)
 			throw StateError("Attempting to call constructor on an already-initialized stream")
 
 		nativeStreamCtor(this, stream, caps)
diff --git a/tools/depgrapher.croc b/tools/depgrapher.croc
index f35f1b8..5f3b30d 100644
--- a/tools/depgrapher.croc
+++ b/tools/depgrapher.croc
@@ -6,7 +6,7 @@ import string: StringBuffer
 
 function as_(c: class) =
 	\i: instance ->
-		(i as c) !is null
+		(i as c) is not null
 
 local cats =
 {
@@ -269,7 +269,7 @@ digraph d
 
 		function cycleColor(c)
 		{
-			if(c !in cycleColors)
+			if(c not in cycleColors)
 			{
 // 				local r, g, b =
 				cycleColors[c] = "\"#{:x2}{:x2}{:x2}\"".format(math.rand(128) + 127, math.rand(128) + 127, math.rand(128) + 127)
@@ -282,7 +282,7 @@ digraph d
 		{
 			if(cat is :ignore)
 				continue
-			else if(cat !is :uncat)
+			else if(cat is not :uncat)
 			{
 				ret.append(@'
 	subgraph cluster_' ~ cat.name ~ @'
@@ -299,7 +299,7 @@ digraph d
 			foreach(mod; cat.modules)
 				ret.formatln("\t\"{}\" [style = filled, fillcolor = {}]", mod.name, mod.cycle ? cycleColor(mod.cycle) : "grey")
 
-			if(cat !is :uncat)
+			if(cat is not :uncat)
 				ret.formatln("\t}")
 
 			foreach(mod; cat.modules)
@@ -355,7 +355,7 @@ digraph d
 
 			foreach(w, _; v.deps)
 			{
-				if(w !in index)
+				if(w not in index)
 				{
 					tarjan(w)
 					lowlink[v] = min(lowlink[v], lowlink[w])
@@ -372,7 +372,7 @@ digraph d
 				{
 					local n = S.pop()
 					cycle.append(n)
-				} while(n !is v)
+				} while(n is not v)
 
 				if(#cycle > 1)
 					foreach(mod; cycle)
@@ -381,7 +381,7 @@ digraph d
 		}
 
 		foreach(mod; :allModules)
-			if(mod !in index)
+			if(mod not in index)
 				tarjan(mod)
 
 		hash.clear(index)