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\LARGE\bf Certified Parsing\\[-10mm]

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\section*{Background}

\noindent

Parsing is the act of transforming plain text into some

structure that can be analysed by computers for further processing.

One might think that parsing has been studied to death and after

\emph{yacc} and \emph{lex} no new results can be obtained in this area.

However recent results and novel approaches make it increasingly clear,

that this is not true anymore.

We propose to approach the subject of parsing from a certification point

of view. Parsers are increasingly part of certified compilers, like \mbox{\emph{CompCert}},

which are guaranteed to be correct and bug-free. Such certified compilers are

crucial in areas where software just cannot fail. However, so far the

parsers of these compilers have been left out of the certification.

This is because parsing algorithms are often adhoc and their semantics

is not clearly specified. Unfortunately, this means parsers can harbour

errors that potentially invalidate the whole certification and correctness

of the compiler. In this project, we like to change that.

Only in the last few years, theorem provers have become good enough

for establishing the correctness of some standard lexing and

parsing algorithms. For this, the algorithms need to be formulated

in way so that it is easy to reason about them. In earlier work

about lexing and regular languages, the authors showed that this

precludes well-known algorithms working over graphs. However regular

languages can be formulated and reasoned about entirely in terms

regular expressions, which can be easily represented in theorem

provers. This work uses the device of derivatives of regular

expressions. We like to extend this device to parsers and grammars.

The aim is to come up with elegant and useful parsing algorithms

whose correctness and the absence of bugs can be certified in a

theorem prover.

\section*{Proposed Work}

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%  \noindent {\bf Objectives:} The overall goals of the project are as follows:

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%  \item To solve the POPLmark challenge.

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%  \item To explore the strengths of this package by proving the

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%  \item To provide a basis for extracting programs from safety proofs.

%  \item To make the nominal datatype package usable for teaching

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