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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:36.0pt">
We all love strong guarantees offered by type checking, but somehow most people shy away from "syntactic type checking" offered by parser generators. Parser combinators are the Python of parsing: Easy to use initially, but a maintenance hell in the long run
for larger projects...<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt">I’d never thought of it that way before – interesting.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs <ghc-devs-bounces@haskell.org>
<b>On Behalf Of </b>Sven Panne<br>
<b>Sent:</b> 09 October 2018 08:23<br>
<b>To:</b> vlad.z.4096@gmail.com<br>
<b>Cc:</b> GHC developers <ghc-devs@haskell.org><br>
<b>Subject:</b> Re: Parser.y rewrite with parser combinators<o:p></o:p></span></p>
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Am Di., 9. Okt. 2018 um 00:25 Uhr schrieb Vladislav Zavialov <<a href="mailto:vlad.z.4096@gmail.com">vlad.z.4096@gmail.com</a>>:<o:p></o:p></p>
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[...] That's true regardless of implementation technique, parsers are rather<br>
delicate.<o:p></o:p></p>
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I think it's not the parsers themselves which are delicate, it is the language that they should recognize.<o:p></o:p></p>
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A LALR-based parser generator does provide more information<br>
when it detects shift/reduce and reduce/reduce conflicts, but I never<br>
found this information useful. It was always quite the opposite of<br>
being helpful - an indication that a LALR parser could not handle my<br>
change and I had to look for workarounds. [...]<o:p></o:p></p>
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Not that this would help at this point, but: The conflicts reported by parser generators like Happy are *extremely* valuable, they hint at tricky/ambiguous points in the grammar, which in turn is a strong hint that the language you're trying to parse has dark
corners. IMHO every language designer and e.g. everybody proposing a syntactic extension to GHC should try to fit this into a grammar for Happy *before* proposing that extension. If you get conflicts, it is a very strong hint that the language is hard to parse
by *humans*, too, which is the most important thing to consider. Haskell already has tons of syntactic warts which can only be parsed by infinite lookahead, which is only a minor technical problem, but a major usablity problem. "Programs are meant to be read
by humans and only incidentally for computers to execute." (D.E.K.) </rant> ;-)<o:p></o:p></p>
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The situation is a bit strange: We all love strong guarantees offered by type checking, but somehow most people shy away from "syntactic type checking" offered by parser generators. Parser combinators are the Python of parsing: Easy to use initially, but a
maintenance hell in the long run for larger projects...<o:p></o:p></p>
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Cheers,<o:p></o:p></p>
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S.<o:p></o:p></p>
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