+\begin{code}
+-- $type_classification
+-- #type_classification#
+--
+-- Types are one of:
+--
+-- [Unboxed] Iff its representation is other than a pointer
+-- Unboxed types are also unlifted.
+--
+-- [Lifted] Iff it has bottom as an element.
+-- Closures always have lifted types: i.e. any
+-- let-bound identifier in Core must have a lifted
+-- type. Operationally, a lifted object is one that
+-- can be entered.
+-- Only lifted types may be unified with a type variable.
+--
+-- [Algebraic] Iff it is a type with one or more constructors, whether
+-- declared with @data@ or @newtype@.
+-- An algebraic type is one that can be deconstructed
+-- with a case expression. This is /not/ the same as
+-- lifted types, because we also include unboxed
+-- tuples in this classification.
+--
+-- [Data] Iff it is a type declared with @data@, or a boxed tuple.
+--
+-- [Primitive] Iff it is a built-in type that can't be expressed in Haskell.
+--
+-- Currently, all primitive types are unlifted, but that's not necessarily
+-- the case: for example, @Int@ could be primitive.
+--
+-- Some primitive types are unboxed, such as @Int#@, whereas some are boxed
+-- but unlifted (such as @ByteArray#@). The only primitive types that we
+-- classify as algebraic are the unboxed tuples.
+--
+-- Some examples of type classifications that may make this a bit clearer are:
+--
+-- @
+-- Type primitive boxed lifted algebraic
+-- -----------------------------------------------------------------------------
+-- Int# Yes No No No
+-- ByteArray# Yes Yes No No
+-- (\# a, b \#) Yes No No Yes
+-- ( a, b ) No Yes Yes Yes
+-- [a] No Yes Yes Yes
+-- @
+
+-- $representation_types
+-- A /source type/ is a type that is a separate type as far as the type checker is
+-- concerned, but which has a more low-level representation as far as Core-to-Core
+-- passes and the rest of the back end is concerned. Notably, 'PredTy's are removed
+-- from the representation type while they do exist in the source types.
+--
+-- You don't normally have to worry about this, as the utility functions in
+-- this module will automatically convert a source into a representation type
+-- if they are spotted, to the best of it's abilities. If you don't want this
+-- to happen, use the equivalent functions from the "TcType" module.
+\end{code}