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0 pointsxscott4y ago0 comments

I'm assuming that uses back-references to handle the matching parens, but I don't like reading regexes (even my own). It's funny that paren matching used to be an example of why you needed to use a push down automata instead of a regular language.

I like your idea for making a prettier lisp quickly, but depending on the language/library, isn't this going to give the a user a bunch of nested `match` objects instead of nicely nested and printable lists?

No free lunch - I guess you trade one ugliness for another.

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6 comments · 2 top-level

kazinator4y ago· 2 in thread

> It's funny that paren matching used to be an example of why you needed to use a push down automata instead of a regular language.

Expressions with parentheses are not a regular language; expressions which can match them are not regular expressions, even if they extend regular expression syntax.

"Regular expression" became the name of a software feature, which retained its name as it was extended beyond regular sets.

Just like "web browser" became the name of a kind of program, and that name still sticks even though it's now a monstrous application platform, not just for browsing.

xscottOP4y ago

I honestly can't tell if you intentionally take stuff out of context so you can argue against it, or if your reading comprehension and logic skills are really just that bad.

I said, "instead of a regular language". You even quoted it. You don't even read the bits that you cut and paste to argue against.

> expressions which can match them are not regular expressions

And that's the damned point. Modern "regular expressions" aren't just "regular" any more. They've had back references and other extensions for a while now:

https://www.regular-expressions.info/balancing.html

https://www.regular-expressions.info/recurse.html

https://www.regular-expressions.info/backref.html

Please - don't reply to me until you take the time to read and understand what I've said.

kazinator4y ago

If "paren matching used to be an example of why you needed to use a push down automata instead of a regular language", isn't that intended to say that this is not the case today? If we change "language" to "expression", then I agree and don't have anything to add. The scope of "regular expression" has increased, in informal usage, but (I strongly suspect) "regular language" still means the same thing as before.

NoThisIsMe4y ago· 2 in thread

GP calls it a tokenizer (aka lexer) so presumably it doesn't match parens, it just returns a flat array of tokens.

xscottOP4y ago

That's disappointing. I don't have any stats, but I imagine 90% of beginners writing an interpreter (much less a compiler) start a lexer and parser and quit before getting to the good stuff.

Skipping the tedium until you've got "hello world" and "factorial working" makes sense to me. You can always go fix the syntax later.

morelisp4y ago

If you don't include the parser, "factorial working" is going to be the same evaluating just about any scripting language. You don't see half the value in Lisp's syntax until you're writing the parser.

j / k navigate · click thread line to collapse

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6 comments · 2 top-level

kazinator4y ago· 2 in thread

> It's funny that paren matching used to be an example of why you needed to use a push down automata instead of a regular language.

Expressions with parentheses are not a regular language; expressions which can match them are not regular expressions, even if they extend regular expression syntax.

"Regular expression" became the name of a software feature, which retained its name as it was extended beyond regular sets.

Just like "web browser" became the name of a kind of program, and that name still sticks even though it's now a monstrous application platform, not just for browsing.

xscottOP4y ago

I honestly can't tell if you intentionally take stuff out of context so you can argue against it, or if your reading comprehension and logic skills are really just that bad.

I said, "instead of a regular language". You even quoted it. You don't even read the bits that you cut and paste to argue against.

> expressions which can match them are not regular expressions

And that's the damned point. Modern "regular expressions" aren't just "regular" any more. They've had back references and other extensions for a while now:

https://www.regular-expressions.info/balancing.html

https://www.regular-expressions.info/recurse.html

https://www.regular-expressions.info/backref.html

Please - don't reply to me until you take the time to read and understand what I've said.

kazinator4y ago

NoThisIsMe4y ago· 2 in thread

GP calls it a tokenizer (aka lexer) so presumably it doesn't match parens, it just returns a flat array of tokens.

xscottOP4y ago

That's disappointing. I don't have any stats, but I imagine 90% of beginners writing an interpreter (much less a compiler) start a lexer and parser and quit before getting to the good stuff.

Skipping the tedium until you've got "hello world" and "factorial working" makes sense to me. You can always go fix the syntax later.

morelisp4y ago

j / k navigate · click thread line to collapse