% against the constructors in the \hs{case} expressions.
We can see two versions of a contrived example below, the first
using a \hs{case} construct and the other using a \hs{if-then-else}
- constructs, in the code below. The example sums two values when they are
- equal or non-equal (depending on the predicate given) and returns 0
- otherwise. Both versions of the example roughly correspond to the same
- netlist, which is depicted in \Cref{img:choice}.
+ constructs, in the code below.
\begin{code}
sumif pred a b = case pred of
\caption{Choice - sumif}
\label{img:choice}
\end{figure}
+
+ The example sums two values when they are equal or non-equal (depending on
+ the predicate given) and returns 0 otherwise. Both versions of the example
+ roughly correspond to the same netlist, which is depicted in
+ \Cref{img:choice}.
A slightly more complex (but very powerful) form of choice is pattern
matching. A function can be defined in multiple clauses, where each clause
% value.
\item[\bf{Multiple constructors with fields}]
Algebraic datatypes with multiple constructors, where at least
- one of these constructors has one or more fields are not
- currently supported.
+ one of these constructors has one or more fields are currently not
+ supported.
\end{xlist}
\subsection{Polymorphism}
\section{\CLaSH\ prototype}
-foo\par bar
+The \CLaSH\ language as presented above can be translated to \VHDL\ using
+the prototype \CLaSH\ compiler. This compiler allows experimentation with
+the \CLaSH\ language and allows for running \CLaSH\ designs on actual FPGA
+hardware.
+
+\begin{figure}
+\centerline{\includegraphics{compilerpipeline.svg}}
+\caption{\CLaSH\ compiler pipeline}
+\label{img:compilerpipeline}
+\end{figure}
+
+The prototype heavily uses \GHC, the Glasgow Haskell Compiler.
+\Cref{img:compilerpipeline} shows the \CLaSH\ compiler pipeline. As you can
+see, the front-end is completely reused from \GHC, which allows the \CLaSH\
+prototype to support most of the Haskell Language. The \GHC\ front-end
+produces the program in the \emph{Core} format, which is a very small,
+functional, typed language which is relatively easy to process.
+
+The second step in the compilation process is \emph{normalization}. This
+step runs a number of \emph{meaning preserving} transformations on the
+Core program, to bring it into a \emph{normal form}. This normal form
+has a number of restrictions that make the program similar to hardware.
+In particular, a program in normal form no longer has any polymorphism
+or higher order functions.
+
+The final step is a simple translation to \VHDL.
\section{Use cases}
As an example of a common hardware design where the use of higher-order
interfaces a designer can simulate electronic systems which have both analog
as digital parts. ForSyDe has several simulation and synthesis backends,
though synthesis is restricted to the synchronous subset of the ForSyDe
-language. Unlike \CLaSH\ there is no support for the automated synthesis of description that contain polymorphism or higher-order functions.
+language. Unlike \CLaSH\ there is no support for the automated synthesis of descriptions that contain polymorphism or higher-order functions.
Lava~\cite{Lava} is a hardware description language that focuses on the
structural representation of hardware. Besides support for simulation and
generators when viewed from a synthesis viewpoint, in that the language
elements of Haskell, such as choice, can be used to guide the circuit
generation. If a developer wants to insert a choice element inside an actual
-circuit he will have to specify this explicitly as a component.
+circuit he will have to explicitly instantiate a multiplexer-like component.
In this respect \CLaSH\ differs from Lava, in that all the choice elements,
such as case-statements and pattern matching, are synthesized to choice
The merits of polymorphic typing, combined with higher-order functions, are
now also recognized in the `main-stream' hardware description languages,
-exemplified by the new \VHDL-2008 standard~\cite{VHDL2008}. \VHDL-2008 has
-support to specify types as generics, thus allowing a developer to describe
+exemplified by the new \VHDL-2008 standard~\cite{VHDL2008}. \VHDL-2008 support for generics has been extended to types, allowing a developer to describe
polymorphic components. Note that those types still require an explicit
-generic map, whereas type-inference and type-specialization are implicit in
-\CLaSH.
+generic map, whereas types can be automatically inferred in \CLaSH.
% Wired~\cite{Wired},, T-Ruby~\cite{T-Ruby}, Hydra~\cite{Hydra}.
%
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