Index: src/AST/Decl.cpp
===================================================================
--- src/AST/Decl.cpp	(revision 9131e5492fda2590328dd083e16ce74d99e1d810)
+++ src/AST/Decl.cpp	(revision 360b2e13b0a6890e0332ced51cb4d18245ed79ae)
@@ -14,12 +14,14 @@
 //
 
-#include <cassert>        // for assert, strict_dynamic_cast
+#include "Decl.hpp"
+
+#include <cassert>             // for assert, strict_dynamic_cast
+#include <string>
 #include <unordered_map>
 
-#include "Decl.hpp"
-
-#include "Fwd.hpp"        // for UniqueId
+#include "Fwd.hpp"             // for UniqueId
 #include "Init.hpp"
-#include "Node.hpp"       // for readonly
+#include "Node.hpp"            // for readonly
+#include "Parser/ParseNode.h"  // for DeclarationNode
 
 namespace ast {
@@ -41,4 +43,21 @@
 	if ( i != idMap.end() ) return i->second;
 	return {};
+}
+
+// --- TypeDecl
+
+std::string TypeDecl::typeString() const {
+	static const std::string kindNames[] = { "object type", "function type", "tuple type" };
+	assertf( sizeof(kindNames)/sizeof(kindNames[0]) == DeclarationNode::NoTypeClass-1, 
+		"typeString: kindNames is out of sync." );
+	assertf( kind < sizeof(kindNames)/sizeof(kindNames[0]), "TypeDecl's kind is out of bounds." );
+	return (sized ? "sized " : "") + kindNames[ kind ];
+}
+
+std::string TypeDecl::genTypeString() const {
+	static const std::string kindNames[] = { "dtype", "ftype", "ttype" };
+	assertf( sizeof(kindNames)/sizeof(kindNames[0]) == DeclarationNode::NoTypeClass-1, "genTypeString: kindNames is out of sync." );
+	assertf( kind < sizeof(kindNames)/sizeof(kindNames[0]), "TypeDecl's kind is out of bounds." );
+	return kindNames[ kind ];
 }
 
Index: src/AST/Decl.hpp
===================================================================
--- src/AST/Decl.hpp	(revision 9131e5492fda2590328dd083e16ce74d99e1d810)
+++ src/AST/Decl.hpp	(revision 360b2e13b0a6890e0332ced51cb4d18245ed79ae)
@@ -115,4 +115,74 @@
 };
 
+/// Base class for named type aliases
+class NamedTypeDecl : public Decl {
+public:
+	ptr<Type> base;
+	std::vector<ptr<TypeDecl>> parameters;
+	std::vector<ptr<DeclWithType>> assertions;
+
+	NamedTypeDecl( const CodeLocation& loc, const std::string& name, Storage::Classes storage, 
+		Type* b, Linkage::Spec spec = Linkage::Cforall )
+	: Decl( loc, name, storage, spec ), base( b ), parameters(), assertions() {}
+
+	/// Produces a name for the kind of alias
+	virtual std::string typeString() const = 0;
+
+private:
+	NamedTypeDecl* clone() const override = 0;
+};
+
+/// Cforall type variable: `dtype T`
+class TypeDecl final : public NamedTypeDecl {
+public:
+	/// type variable variants. otype is a specialized dtype
+	enum Kind { Dtype, Ftype, Ttype, NUMBER_OF_KINDS } kind;
+	bool sized;
+	ptr<Type> init;
+
+	/// Data extracted from a type decl
+	struct Data {
+		Kind kind;
+		bool isComplete;
+
+		Data() : kind( (Kind)-1 ), isComplete( false ) {}
+		Data( TypeDecl* d ) : kind( d->kind ), isComplete( d->sized ) {}
+		Data( Kind k, bool c ) : kind( k ), isComplete( c ) {}
+		Data( const Data& d1, const Data& d2 ) 
+		: kind( d1.kind ), isComplete( d1.isComplete || d2.isComplete ) {}
+
+		bool operator== ( const Data& o ) const {
+			return kind == o.kind && isComplete == o.isComplete;
+		}
+		bool operator!= ( const Data& o ) const { return !(*this == o); }
+	};
+
+	TypeDecl( const CodeLocation& loc, const std::string& name, Storage::Classes storage, Type* b, 
+		Kind k, bool s, Type* i = nullptr )
+	: NamedTypeDecl( loc, name, storage, b ), kind( k ), sized( k == Ttype || s ), init( i ) {}
+
+	std::string typeString() const override;
+	/// Produces a name for generated code
+	std::string genTypeString() const;
+
+	Decl* accept( Visitor& v ) override { return v.visit( this ); }
+private:
+	TypeDecl* clone() const override { return new TypeDecl{ *this }; }
+};
+
+/// C-style typedef `typedef Foo Bar`
+class TypedefDecl final : public NamedTypeDecl {
+public:
+	TypedefDecl( const CodeLocation& loc, const std::string& name, Storage::Classes storage, 
+		Type* b, Linkage::Spec spec = Linkage::Cforall )
+	: NamedTypeDecl( loc, name, storage, b, spec ) {}
+
+	std::string typeString() const override { return "typedef"; }
+
+	Decl* accept( Visitor& v ) override { return v.visit( this ); }
+private:
+	TypedefDecl* clone() const override { return new TypedefDecl{ *this }; }
+};
+
 /// Aggregate type declaration base class
 class AggregateDecl : public Decl {
Index: src/AST/porting.md
===================================================================
--- src/AST/porting.md	(revision 9131e5492fda2590328dd083e16ce74d99e1d810)
+++ src/AST/porting.md	(revision 360b2e13b0a6890e0332ced51cb4d18245ed79ae)
@@ -89,4 +89,7 @@
   * allows `newObject` as just default settings
 
+`TypeDecl`
+* stripped `isComplete()` accessor in favour of direct access to `sized`
+
 `EnumDecl`
 * **TODO** rebuild `eval` for new AST (re: `valueOf` implementation)