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I have a fundamental question: What happened to the idea of specifying the syntax of a language using a "formal" grammar, however terribly flawed and imperfect

by kaby76 5y ago

I have a fundamental question: What happened to the idea of specifying the syntax of a language using a "formal" grammar, however terribly flawed and imperfect that has been--for decades--and still is? It seems that if you need a grammar, e.g., to write a programming language tool, it's considered "old school". If it's published, it's of secondary consideration because it's usually out-of-sync with the implementation (e.g., C#, soon to be version 10, the latest "spec"--draft at that--version 6). Some don't even bother publishing a grammar, e.g., Julia. Why would the authors of Julia not publish a "formal" grammar of any kind, instead just offer a link to the 2500+ lines of Scheme-like code? Are we to now write tools to machine-scrape the grammar from the hand-written code or derive the grammar from a ML model of the compiler?

saurik 5y ago
One big reason is because it is highly likely they not only don't have one, but one couldn't even exist in any meaningful way, as their primary implementation is some turing-complete monstrosity where the only "formal" spec is their code as there is nothing "formal" about it: the cost of not using parser generators is essentially the same as the cost of using dynamic typing... it not only means you probably have inconsistency bugs all over the place, even if it made it feel easier to code without having to actually prove your program was correct all the time, but it further tends to lead you to relying on the dynamic typing features in places that make the resulting program not something that fits any known formal type model anymore even if it works perfectly.
ChrisRackauckas 5y ago
Who is going to put the time in to maintain it if the language is given by the implementation of the language? In the past, people wrote huge specs because you wanted multiple companies to implement compilers for their various computers. Now there's enough centralization that a single implementation of a language can exist. Why spend the time supporting 6 compilers when 99.99% of users will use the big 1 that the core language developers are working on? Labor is a finite resource, and because this requirement is gone the extra work that came with that requirement is discarded as well. If someone was willing to write up a full spec and maintain it for 10 years then I am sure it would be accepted to any open source language, but nobody decides to do that with their free time for some reason.

by kaby76 5y ago

saurik 5y ago

One big reason is because it is highly likely they not only don't have one, but one couldn't even exist in any meaningful way, as their primary implementation is some turing-complete monstrosity where the only "formal" spec is their code as there is nothing "formal" about it: the cost of not using parser generators is essentially the same as the cost of using dynamic typing... it not only means you probably have inconsistency bugs all over the place, even if it made it feel easier to code without having to actually prove your program was correct all the time, but it further tends to lead you to relying on the dynamic typing features in places that make the resulting program not something that fits any known formal type model anymore even if it works perfectly.

ChrisRackauckas 5y ago

Who is going to put the time in to maintain it if the language is given by the implementation of the language? In the past, people wrote huge specs because you wanted multiple companies to implement compilers for their various computers. Now there's enough centralization that a single implementation of a language can exist. Why spend the time supporting 6 compilers when 99.99% of users will use the big 1 that the core language developers are working on? Labor is a finite resource, and because this requirement is gone the extra work that came with that requirement is discarded as well. If someone was willing to write up a full spec and maintain it for 10 years then I am sure it would be accepted to any open source language, but nobody decides to do that with their free time for some reason.