\blank[medium]
\startcitedquotation[deursen00]
- A domain-specific language (\small{DSL}) is a program-
- ming language or executable specification language
- that offers, through appropriate notations and ab-
- stractions, expressive power focused on, and usu-
- ally restricted to, a particular problem domain.
+ A domain-specific language (\small{DSL}) is a programming language
+ or executable specification language that offers, through
+ appropriate notations and abstractions, expressive power focused
+ on, and usually restricted to, a particular problem domain.
\stopcitedquotation
An embedded \small{DSL} is a \small{DSL} that is embedded in
polymorphism, higher-order values or type classes can be used in
the embedded language. \cite[hudak96]
- For an \small{EDSL}, the definitions of compiletime and runtime
+ For an \small{EDSL}, the definitions of compile-time and run-time
are typically fuzzy (and thus hard to define here), since the
\small{EDSL} \quote{compiler} is usually compiled by the same
Haskell compiler as the \small{EDSL} program itself.
this not been done before?}. Using a functional language for describing hardware
is not a new idea at all. In fact, there has been research into functional
hardware description even before the conventional hardware description
- languages were created. Examples of these are µFP \cite[sheeran83] and
+ languages were created. Examples of these are µFP \cite[sheeran83]\ and
Ruby \cite[jones90]. Functional languages were not nearly as advanced
as they are now, and functional hardware description never really got
off.
Recently, there have been some renewed efforts, especially using the
- Haskell functional language. Examples are Lava \cite[claessen00] (an
- \small{EDSL}) and ForSyde \cite[sander04] (an \small{EDSL} using
- Template Haskell). \cite[baaij09] has a more complete overview of the
+ Haskell functional language. Examples are Lava \cite[claessen00]\ (an
+ \small{EDSL}) and ForSyde \cite[sander04]\ (an \small{EDSL} using
+ Template Haskell). \cite[baaij09]\ has a more complete overview of the
current field.
We will now have a look at the existing hardware description languages,
define limitations on values, making it easier to find violations
and thus bugs.
\item Easy to process. Functional languages have nice properties like
- purity \refdef{purity} and single binding behaviour, which make it easy
+ purity \refdef{purity} and single binding behavior, which make it easy
to apply program transformations and optimizations and could potentially
simplify program verification.
\stopitemize
+ \section[sec:context:fhdls]{Existing functional hardware description languages}
+ As noted above, this path has been explored before. However, current
+ embedded functional hardware description languages (in particular
+ those using Haskell) are limited. Below a number of downsides are
+ sketched of the recent attempts using the Haskell language.
+ \cite[baaij09]\ has a more complete overview of these and other
+ languages.
+
+ This list uses Lava and ForSyDe as examples, but tries to generalize
+ the conclusions to the techniques of embedding a \small{DSL} and
+ using Template Haskell.
+
\placeintermezzo{}{
\defref{Template Haskell}
\startframedtext[width=8.5cm,background=box,frame=no]
\stopalignment
\blank[medium]
- Template Haskell is an extension to the \GHC compiler that allows
+ Template Haskell is an extension to the \GHC\ compiler that allows
a program to mark some parts to be evaluated \emph{at compile
time}. These \emph{templates} can then access the abstract syntax
tree (\small{AST}) of the program that is being compiled and
generate parts of this \small{AST}.
Template Haskell is a very powerful, but also complex mechanism.
- It was inteded to simplify the generation of some repetive pieces
+ It was intended to simplify the generation of some repetitive pieces
of code, but its introspection features have inspired all sorts of
applications, such as hardware description compilers.
\stopframedtext
}
- \section[sec:context:fhdls]{Existing functional hardware description languages}
- As noted above, this path has been explored before. However, current
- embedded functional hardware description languages (in particular
- those using Haskell) are limited. Below a number of downsides are
- sketched of the recent attempts using the Haskell language.
- \cite[baaij09] has a more complete overview of these and other
- languages.
-
- This list uses Lava and ForSyDe as examples, but tries to generalize
- the conclusions to the techniques of embedding a \small{DSL} and
- using Template Haskell.
-
\startitemize
\item Not all of Haskell's constructs can be captured by embedded domain
specific languages. For example, an \hs{if} or \hs{case}
expression is typically executed once when the Haskell description
is processed and only the result is reflected in the generated
- datastructure (and thus in the final program). In Lava, for
+ data-structure (and thus in the final program). In Lava, for
example, conditional assignment can only be described by using
explicit multiplexer components, not using any of Haskell's
compact mechanisms (such as \hs{case} expressions or pattern
with an \small{EDSL} approach, it can get confusing when to use
\small{TH} and when not to.
\item Function hierarchies cannot be observed in an \small{EDSL}.
- For example, Lava generates a single flat \VHDL architecture,
+ For example, Lava generates a single flat \VHDL\ architecture,
which has no structure whatsoever. Even though this is strictly
correct, it offers no support to the synthesis software about
which parts of the system can best be placed together and makes
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