Readit NewsOr, in other words: if you "just" want a utility that can learn speech on the fly, you don't need a rigid grammar checker, just a good enough approximator. If you want to check if a document contains errors, you need to define what an error is, and then if you want to define it in a strict manner, at that point you need a rule engine of some sort instead of something probabilistic.
I find that clear-cut, rigid rules tend to be the least helpful ones in writing. Obviously this class of rule is also easy/easier to represent in software, so it also tends to be the source of false positives and frustration that lead me to disable such features altogether.
When writing for utility and communication, though, English grammar is simple and standard enough. Browsing Harper sources, https://github.com/Automattic/harper/blob/0c04291bfec25d0e93... seems to have a lot of the basics already nailed down. Natural language grammar can often be represented as "what is allowed to, should, or should not, appear where, when, and in which context" - IIUC, Harper seems to tackle the problem the same way.
(^^ alien language that was developed in less than a decade)
Also, it takes at most few developers to write those rules into a grammar checking system, compared to millions and more that need to learn a given piece of "evolved" language as it becomes impossible to avoid learning it. It's not only fast enough to do this manually, it also takes much less work-intensive and more scalable.
Languages are used to successfully communicate. To achieve this, all parties involved in the communication must know the language well enough to send and receive messages. This obviously includes messages that transmit changes in the language, for instance, if you tried to explain to your parents the meaning of the current short-lived meme and fad nouns/adjectives like "skibidi ohio gyatt rizz".
It takes time for a language feature to become widespread and de-facto standardized among a population. This is because people need to asynchronously learn it, start using it themselves, and gain critical mass so that even people who do not like using that feature need to start respecting its presence. This inertia is the main source of slowness that I mention, and also and a requirement for any kind of grammar-checking software. From the point of such software, a language feature that (almost) nobody understands is not a language feature, but an error.
> You also seem to be making an assumption that natural languages (English, I'm assuming) can be well defined by a simple set of rigid patterns/rules?
Yes, that set of patterns is called a language grammar. Even dialects and slangs have grammars of their own, even if they're different, less popular, have less formal materials describing them, and/or aren't taught in schools.
Blocks are parsed in the following way: when we get the beginning count of block opening characters, we move Y by one, loop right while whitespace, until we encounter ending count of block characters.
In transposed block, we just switch X and Y, it is easily done with pointers, and use the same code.
(fst-atom """ trd-atom frt-atom
""" 00001
asdf 00002 """ fth-atom)
qwer 00003 hahaha
zxcv """ hehehe
""" hohoho
"""
#lang 2d racket
(require 2d/match)
(define (subtype? a b)
#2dmatch
╔══════════╦══════════╦═══════╦══════════╗
║ a b ║ 'Integer ║ 'Real ║ 'Complex ║
╠══════════╬══════════╩═══════╩══════════╣
║ 'Integer ║ #t ║
╠══════════╬══════════╗ ║
║ 'Real ║ ║ ║
╠══════════╣ ╚═══════╗ ║
║ 'Complex ║ #f ║ ║
╚══════════╩══════════════════╩══════════╝)