Strings do too many things

Any time you're turning a string of input into something else, what you are doing is parsing.

Even if the word "parser" never appears in your code, the act of interpreting a string as structured data is parsing, and the code that does parsing is a parser.

Programmers write parsers quite a lot, and many of the parsers they write are ad-hoc, ill-specified, bug-ridden, and can't tell you why your input didn't parse right.

Writing a parser without realizing you're writing a parser, usually leads to writing a bad parser. Bad parsers do things like accepting malformed input that causes security holes. When bad parsers do reject malformed input, they rarely emit useful error messages about why it's malformed. Bad parsers are often written using regex and duct tape.

Try not to write bad parsers. If you need to parse something, consider writing a grammar and using a parser library. (If you're very ambitious, try a parser combinator library.) But at least try to recall something about parsers you learned once way back in a CS class, before throwing regex at the problem and calling it a day.

(And now the word "parser" no longer makes sense, because of semantic satiation.)

By the way, please don't write regex to try to validate email addresses. Seriously. There are libraries for that; some of them are even good. When people write their own regex to match email addresses, they do things like forget that the hyphen is a valid character in domain names.

By the way, please don’t write regex to try to validate email addresses. Seriously.

Amen.

There are libraries for that; some of them are even good.

Spoiler alert: Few of them are good, and those few are so simple that you might as well not use a library.

The only way to correctly validate an email address is to send a message to it, and verify that it arrived.
- You can use a regex to do basic validation. That regex is .+@.+. Anything beyond that is a waste of time.
- The only way to correctly validate an email address is to send a message to it, and verify that it arrived.
  
  If you're accepting email addresses as user input (e.g. from a web form), it might be nice to check that what's to the right of the rightmost @ sign is a domain name with an MX or A record. That way, if a user enters a typo'd address, you have some chance of telling them that instead of handing an email to user#example.net or [email protected] to your MTA.
  
  But the validity of the local-part (left of the rightmost @) is up to the receiving server.
By the way, please don’t write regex to try to validate email addresses. Seriously.

Speaking of things you can't parse with regex...

You can't parse [X]HTML with regex. Because HTML can't be parsed by regex. Regex is not a tool that can be used to correctly parse HTML. As I have answered in HTML-and-regex questions here so many times before, the use of regex will not allow you to consume HTML. Regular expressions are a tool that is insufficiently sophisticated to understand the constructs employed by HTML. HTML is not a regular language and hence cannot be parsed by regular expressions. Regex queries are not equipped to break down HTML into its meaningful parts. so many times but it is not getting to me. Even enhanced irregular regular expressions as used by Perl are not up to the task of parsing HTML. You will never make me crack. HTML is a language of sufficient complexity that it cannot be parsed by regular expressions. Even Jon Skeet cannot parse HTML using regular expressions. Every time you attempt to parse HTML with regular expressions, the unholy child weeps the blood of virgins, and Russian hackers pwn your webapp. Parsing HTML with regex summons tainted souls into the realm of the living. HTML and regex go together like love, marriage, and ritual infanticide. The <center> cannot hold it is too late. The force of regex and HTML together in the same conceptual space will destroy your mind like so much watery putty. If you parse HTML with regex you are giving in to Them and their blasphemous ways which doom us all to inhuman toil for the One whose Name cannot be expressed in the Basic Multilingual Plane, he comes. HTML-plus-regexp will liquify the nerves of the sentient whilst you observe, your psyche withering in the onslaught of horror. Rege̿̔̉x-based HTML parsers are the cancer that is killing StackOverflow it is too late it is too late we cannot be saved the transgression of a chi͡ld ensures regex will consume all living tissue (except for HTML which it cannot, as previously prophesied) dear lord help us how can anyone survive this scourge using regex to parse HTML has doomed humanity to an eternity of dread torture and security holes using regex as a tool to process HTML establishes a breach between this world and the dread realm of c͒ͪo͛ͫrrupt entities (like SGML entities, but more corrupt) a mere glimpse of the world of regex parsers for HTML will instantly transport a programmer's consciousness into a world of ceaseless screaming, he comes, the pestilent slithy regex-infection will devour your HTML parser, application and existence for all time like Visual Basic only worse he comes he comes do not fight he com̡e̶s, ̕h̵is un̨ho͞ly radiańcé destro҉ying all enli̍̈́̂̈́ghtenment, HTML tags lea͠ki̧n͘g fr̶ǫm ̡yo͟ur eye͢s̸ ̛l̕ik͏e liquid pain, the song of re̸gular expression parsing will extinguish the voices of mortal man from the sphere I can see it can you see ̲͚̖͔̙î̩́t̲͎̩̱͔́̋̀ it is beautiful the final snuffing of the lies of Man ALL IS LOŚ͖̩͇̗̪̏̈́T ALL IS LOST the pon̷y he comes he c̶̮omes he comes the ichor permeates all MY FACE MY FACE ᵒh god no NO NOO̼OO NΘ stop the an*̶͑̾̾̅ͫ͏̙̤g͇̫͛͆̾ͫ̑͆l͖͉̗̩̳̟̍ͫͥͨe̠̅s ͎a̧͈͖r̽̾̈́͒͑e not rè̑ͧ̌aͨl̘̝̙̃ͤ͂̾̆ ZA̡͊͠͝LGΌ ISͮ̂҉̯͈͕̹̘̱ TO͇̹̺ͅƝ̴ȳ̳ TH̘Ë͖́̉ ͠P̯͍̭O̚N̐Y̡ H̸̡̪̯ͨ͊̽̅̾̎Ȩ̬̩̾͛ͪ̈́̀́͘ ̶̧̨̱̹̭̯ͧ̾ͬC̷̙̲̝͖ͭ̏ͥͮ͟Oͮ͏̮̪̝͍M̲̖͊̒ͪͩͬ̚̚͜Ȇ̴̟̟͙̞ͩ͌͝S̨̥̫͎̭ͯ̿̔̀ͅ

Have you tried using an XML parser instead?
- The best validation for a valid email address is always sending a verification mail. I've rejected countless MRs that contained ad-hoc regex email validation copied from the internet. I'd allow a check for it to contain an @.
Programmers write parsers quite a lot

Speak for yourself. I've done it exactly once. It didn't work, and never shipped. Learned my lesson and always use a parser that someone else wrote. Usually a big team of at least thousands of people (how many people have worked on JSON? Millions? What about UTF8? Those are the main two I use).
- So you have never iterated over command line arguments and tried to identify options? Or taken a string input field?

As a physicist, I agree ;)

Strings became ubiquitously used for a reason, they map really clearly to the way we think as humans. Most importantly, when you’re debugging, seeing string data is much friendlier than whatever data your symbols map to (usually integers, from enum structures)

No, obviously it’s not the most efficient thing in the world, but it hardly matters, and you’re not getting anyone to stop because you’re “technically right”.

Symbols display with friendly string-y names in a number of languages. Clojure, for example, has a symbol type.

And a number of languages display friendly strings for enumy things - Scala, Haskell, and Rust spring to mind.

The problem with strings over enums with a nice debugging display is that the string type is too wide. Strings don't tell you what values are valid, strings don't catch typos at compile time, and they're murder when refactoring.

Clojure symbols are good at differentiation between symbolly things and strings, though they don't catch typos.

The other problem the article mentions is strings over a proper struct/adt/class hierarchy is that strings don't really have any structure to them. Concatenating strings is brittle compared to building up an AST then rendering it at the end.

Edit: autocorrect messed a few things up I didn't catch.

Despite all my rage I'm still just some bytes in a page

Man, stop overthinking stuff.

Unless you're using assembly, strings do everything, since the code files are also strings.

…and that’s why it is wise to use monadic parsers at the input boundary.

Is that your theory?