Ohm: Parsing Made Easy
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Ohm: Parsing Made Easy
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Re: Ohm: Parsing Made Easy
#2I’ve used Ohm for a few small parsers. What’s great about the editor is that you can take it and share it with somebody else and they’re given insights into _how_ the parser works.
Re: Ohm: Parsing Made Easy
#3"Further reading" links at the bottom just link back to the same page.
Re: Ohm: Parsing Made Easy
#4"Further reading" links at the bottom just link back to the same page.
Thanks. Fixed!
Re: Ohm: Parsing Made Easy
#5[deleted]
Re: Ohm: Parsing Made Easy
#6Hi HN, I'm a researcher at HARC (https://harc.ycr.org/) and one of the authors of Ohm. We've used it to power several of our programming language investigations, such as Seymour (which was on HN yesterday: https://news.ycombinator.com/item?id=15471954) and Chorus (http://www.chorus-home.org/).
If you're interested, here's the grammar for the language used in the Seymour demo: https://github.com/harc/seymour/blob/6f55361ad3410f42f67f183...
Happy to answer any questions that you have!
Re: Ohm: Parsing Made Easy
#7> The Ohm language is based on parsing expression grammars (PEGs), which are a formal way of describing syntax, similar to regular expressions and context-free grammars
Uh-oh. I've voiced my concerns about PEGs (and LL parsers) before, but IMO any grammar "interpreter" that doesn't point out the ambiguities in grammar and instead relies on some vague, and ultimately arbitrary, notion of "precedence" (e.g. that rules declared first in the grammar file have priority), isn't a good foundation for a serious language (good for throwaway parsers and language experiments, though).
Re: Ohm: Parsing Made Easy
#8> The Ohm language is based on parsing expression grammars (PEGs), which are a formal way of describing syntax, similar to regular expressions and context-free grammars Uh-oh. I've voiced my concerns about PEGs (and LL parsers) before, but IMO any grammar "interpreter" that doesn't point out the ambiguities in grammar and instead relies on some vague, and ultimately arbitrary, notion of "precedence" (e.g. that rules…
Is this a limitation of the PEG syntax itself? IOW, is it possible to identify ambiguities in grammars defined as PEGs?
Re: Ohm: Parsing Made Easy
#9Hi HN, I'm a researcher at HARC ( https://harc.ycr.org/ ) and one of the authors of Ohm. We've used it to power several of our programming language investigations, such as Seymour (which was on HN yesterday: https://news.ycombinator.com/item?id=15471954 ) and Chorus ( http://www.chorus-home.org/ ). If you're interested, here's the grammar for the language used in the Seymour demo: https://github.com/harc/seymour/blob…
Nice project, thanks for sharing. One interesting application that comes to mind is creating a "safe" subset of Javascript, that could be run in an end-users browser without requiring a sandbox. One definition of safe might be: not allowing access to the DOM or global variables.
Is this a reasonable use case? Is Ohm's executing environment appropriate for this usecase?
Re: Ohm: Parsing Made Easy
#10> The Ohm language is based on parsing expression grammars (PEGs), which are a formal way of describing syntax, similar to regular expressions and context-free grammars Uh-oh. I've voiced my concerns about PEGs (and LL parsers) before, but IMO any grammar "interpreter" that doesn't point out the ambiguities in grammar and instead relies on some vague, and ultimately arbitrary, notion of "precedence" (e.g. that rules…
Is this a limitation of the PEG syntax itself? IOW, is it possible to identify ambiguities in grammars defined as PEGs?
Possible? Maybe.
But the problem is more that, (according to Wikipedia), the choice operator in PEGs (i.e. e1 | e2) is in fact defined as ordered choice, i.e. it prefers the first alternative.
They try to sell this as a "solution" to ambiguous grammars, as an advantage, but they're just ... wrong. It's as if Java, when resolving method overloading, arbitrarily prefered the method that's declared first in the source file, instead of refusing to compile ambiguous code, as it does now.