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Daniel Hillerström
2021-02-01 13:50:26 +00:00
parent eea76a0979
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thesis.tex
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@@ -4944,7 +4944,7 @@ The $\Absurd$ computation term is used to coerce the return type
$\ZeroType$ of $\Fail$ into $\alpha$. This coercion is safe, because
$\ZeroType$ is an uninhabited type.
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An interpretation of $\Fail$ amounts to implementing an exception
An interpretation of $\Exit$ amounts to implementing an exception
handler.
%
\[
@@ -6644,11 +6644,30 @@ We can now plug it all together.
\ea
\]
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Alice makes a hard copy of the file \texttt{ritchie.txt} as
\texttt{ritchie}, and subsequently removes the original file, which
effectively amounts to a roundabout way of renaming a file. Bob makes
a soft copy of the file \texttt{hamlet} as \texttt{act3}, meaning
both names share the same i-node with index $2$.
Alice copies the file \texttt{ritchie.txt} as \texttt{ritchie}, and
subsequently removes the original file, which effectively amounts to a
roundabout way of renaming a file. It is evident from the file system
state that the file is a hard copy as the contents of
\texttt{ritchie.txt} now reside in location $3$ rather than location
$1$ in the data region. Bob makes a soft copy of the file
\texttt{hamlet} as \texttt{act3}, which is evident by looking at the
directory where the two filenames point to the same i-node (with index
$2$), whose link counter has value $2$.
\paragraph{Summary} Starting from a simple file I/O model we seen how
the modularity of effect handlers enable us to develop a \UNIX{}-style
operating system in an incremental way by composing several handlers
to implement a basic file system, multi-user environments, and
multi-tasking support. Each incremental change to the system has been
backwards compatible with previous changes in the sense that we have
not modified any previously defined interfaces in order to support a
new feature. It serves as a testament to demonstrate the versatility
of effect handlers, and it suggests that handlers can be a viable
option to use with legacy code bases to retrofit functionality. The
operating system uses a total of 14 operations, which are being
handled by 12 handlers, some of which are used multiple times,
e.g. the $\environment$ and $\redirect$ handlers.
% \begin{figure}[t]
% \centering