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<meta property="og:description" content="As I mentioned in an [earlier post]({% post_url 2017-08-16-tapl %}), I’ve been working through Types and Programming Languages in Rust. Chapters 5 to 7 of TAPL discuss untyped lambda calculus through an implementation of a simple expression-based language. Chapter 5 lays the foundations; chapter 6 focuses more on one of the concepts introduced in chapter 5; de Bruijn index and chapter 7 explores an ML implementation of the said language, but only how to evaluate the terms, and not how to parse them. The accompanying OCaml implementation’s parser is generated automatically from a Yacc grammar.
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<a href="http://localhost:1313/post/2017-08-24-untyped-lambda-calculus/">Untyped Lambda Calculus</a>
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<div class="post-meta"><time class="post-date">2017-08-24</time></div>
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#<a href="http://localhost:1313/tags/tapl/">tapl</a>
#<a href="http://localhost:1313/tags/rust/">rust</a>
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<p>As I mentioned in an [earlier post]({% post_url 2017-08-16-tapl %}), I’ve been working through <a href="https://www.cis.upenn.edu/~bcpierce/tapl/">Types and Programming Languages</a> in Rust. Chapters 5 to 7 of TAPL discuss untyped lambda calculus through an implementation of a simple expression-based language. Chapter 5 lays the foundations; chapter 6 focuses more on one of the concepts introduced in chapter 5; <a href="https://en.wikipedia.org/wiki/De_Bruijn_index">de Bruijn index</a> and chapter 7 explores an ML implementation of the said language, but only how to evaluate the terms, and not how to parse them. The accompanying OCaml <a href="https://www.cis.upenn.edu/~bcpierce/tapl/checkers/">implementation</a>’s parser is generated automatically from a Yacc grammar.</p>
<p>I’ve had good experiences writting parsers in Haskell using <a href="https://hackage.haskell.org/package/parsec">parsec</a> and <a href="https://hackage.haskell.org/package/attoparsec">attoparsec</a> before, so I started looking for parser-combinators in Rust. There seem to be three capable options:</p>
<ul>
<li><a href="https://github.com/Marwes/combine">combine</a></li>
<li><a href="https://github.com/m4rw3r/chomp">chomp</a></li>
<li><a href="https://github.com/Geal/nom">nom</a></li>
</ul>
<p>Combine even has the <a href="https://github.com/Marwes/combine-language">combine-language</a> extension which is very similar to Parsec’s <a href="http://hackage.haskell.org/package/parsec/docs/Text-Parsec-Token.html">Text.Parsec.Token</a> which would’ve simplified the task of parsing lexical elements but I couldn’t add it as a dependency to my project—due to compile errors which I’m sure has been because of my ignorance and lack of familiarity with Rust and Cargo. At the end I ended up choosing using layman’s metrics, number of GitHub stars and nom won by a huge margin.</p>
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