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