This propagation makes higher order values become applied (in
particular both of the alternatives of the case now have a
- representable type. Completely applied top level functions (like the
+ representable type). Completely applied top level functions (like the
first alternative) are now no longer invalid (they fall under
\in{item}[item:completeapp] above). (Completely) applied lambda
abstractions can be removed by β-abstraction. For our example,
\todo{Examples. Perhaps reference the previous sections}
-
\section{Unsolved problems}
The above system of transformations has been implemented in the prototype
and seems to work well to compile simple and more complex examples of
transformations will probably need updating to handle them in all
cases.
+ \subsection{Normalization of stateful descriptions}
+ Currently, the intended normal form definition\refdef{intended
+ normal form definition} offers enough freedom to describe all
+ valid stateful descriptions, but is not limiting enough. It is
+ possible to write descriptions which are in intended normal
+ form, but cannot be translated into \VHDL in a meaningful way
+ (\eg, a function that swaps two substates in its result, or a
+ function that changes a substate itself instead of passing it to
+ a subfunction).
+
+ It is now up to the programmer to not do anything funny with
+ these state values, whereas the normalization just tries not to
+ mess up the flow of state values. In practice, there are
+ situations where a Core program that \emph{could} be a valid
+ stateful description is not translateable by the prototype. This
+ most often happens when statefulness is mixed with pattern
+ matching, causing a state input to be unpacked multiple times or
+ be unpacked and repacked only in some of the code paths.
+
+ \todo{example?}
+
+ Without going into detail about the exact problems (of which
+ there are probably more than have shown up so far), it seems
+ unlikely that these problems can be solved entirely by just
+ improving the \VHDL state generation in the final stage. The
+ normalization stage seems the best place to apply the rewriting
+ needed to support more complex stateful descriptions. This does
+ of course mean that the intended normal form definition must be
+ extended as well to be more specific about how state handling
+ should look like in normal form.
+
\section[sec:normalization:properties]{Provable properties}
When looking at the system of transformations outlined above, there are a
number of questions that we can ask ourselves. The main question is of course:
projects / matthijs / master-project / report.git / blobdiff