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0 pointsroenxi7y ago0 comments

The great irony is that elisp, as with most of the languages of its venerable era, is not very good at processing text.

One of my emacs experiences is playing "escaping the regex" about once annually, where I need to use backslashes in a regex, but first have to escape an emacs string.

I'm not very good at elisp, so this is what a basic begineer regex looks like to escape a ' in a shell (so, I want the bash command to go from ' to \'). The regex in emacs I came up with was: (replace-regexp-in-string "'" "'\\\\''" $)

Now maybe there is some sort of shortcut for passing a string straight to a regex that will make me look silly, but for a text editor with emacs' power and flexibility to make a regex look that hard bought a smile to my face.

0 comments

triska7y ago

Emacs has dedicated functions that let you handle such cases more conveniently. For example, in your case, the function regexp-quote may be useful:

    (regexp-quote "\\") ⇒ "\\\\"

In addition, structured data are often better represented as trees. In Emacs, you can use the function "rx" to translate Lisp forms from a dedicated tree-based mini language into regexp strings. The primary advantage is that you can more readily reflect the logic of the intended regular expression in this way.

For example:

    (rx (or "a" "b")) ⇒ "[ab]"

and:

    (rx (and (or "a" "b" "test") "c")) ⇒ "\\(?:test\\|[ab]\\)c"

justinhj7y ago

It never ceases to amaze me how much there is to emacs and emacs-lisp. After 15 years of daily use I still discover gems like this

roenxiOP7y ago

Thankyou

taeric7y ago

I'd be curious what you think are good languages at processing text. A sibling post points out that you are probably just not using some functions that would help. To that end, look into them. I suspect the problem is that you are wanting tools from your current toolbox to look a lot more familiar, though. Hence why I am asking what languages you think are good at processing text.

Elisp is odd to me, because you need to get used to thinking in terms of buffers of text. Most commands require a trip through a buffer. Which is not at all bad, but is very foreign to my expected view.

That said, once you get used to basically programming how you interact with a buffer, it does get very fast very quickly. And can often read rather nicely.

roenxiOP7y ago

Well, I suppose there are two ways to be 'good at processing text'. The first way is to quickly and efficiently let the user do what they want, which is how Python approaches the problem, eg, str[0:len(str)-1] + "'\''". I've only learned python in the last 12 months, and I need access to a lot less documentation than I need in elisp to write that.

The second way is to have a model that is so strong that it is worth the user learning that model (this is a rarer approach, but is more common in the lisp families - Clojure, for example, does this with variables). If elisp has this, it would be a good idea for someone to mention that in the documentation, because I don't recall ever seeing anyone say "Wow! This elisp model of processing text is amazing! I've been doing it wrong my whole life!". I have seen variants of "which is not at all bad, but is very foreign".

I don't know of a best language, but manipulating text strings is the foundation of most web serving. So I'd say that the popular languages for that (python, perl, php, etc) are quite a bit better than elisp at processing text.

taeric7y ago

This actually takes it in a direction I disagree with.

Once you get used to manipulating buffers, elisp actually is easier than most other languages. What it is bad at is processing strings. Because it is good at processing text buffers.

I am on my phone, but if this thread is still going this evening, I'll show roughly what that snippet would look like. Will be, roughly, (forward-word) (move -1) (insert "/"). Obviously, some differences if you were moving words or paragraphs. But basic idea is the same.

That is, don't try and manipulate strings. Manipulate the entire buffer. If needed, build a new buffer with what all you want.

The irony is that elisp has a decent dsl for manipulating text. But you have to embrace the mutable nature of it. Which is unexpected for many working with a lisp.

kazinator7y ago

TXR Lisp is a dialect that has decent features for munging text. It's part of a two-language combination called TXR; the other language is the TXR Pattern Language: a notation for matching small and large scale structures in text documents and streams.

TXR Lisp allows various classic Lisp operations to also be used on vectors and strings (think car, cdr, mapcar* and numerous others). It has array referencing that support Python's negative index convention. Sequence subranges are assignable places, so if s holds "firetruck" then (set [s 1..-1] "lic") changes s to "flick".

TXR Lisp is loaded with useful features, all packed into a small executable accompanied by a small library of Lisp files.

j / k navigate · click thread line to collapse

0 comments

triska7y ago

Emacs has dedicated functions that let you handle such cases more conveniently. For example, in your case, the function regexp-quote may be useful:

    (regexp-quote "\\") ⇒ "\\\\"

For example:

    (rx (or "a" "b")) ⇒ "[ab]"

and:

    (rx (and (or "a" "b" "test") "c")) ⇒ "\\(?:test\\|[ab]\\)c"

justinhj7y ago

It never ceases to amaze me how much there is to emacs and emacs-lisp. After 15 years of daily use I still discover gems like this

roenxiOP7y ago

Thankyou

taeric7y ago

That said, once you get used to basically programming how you interact with a buffer, it does get very fast very quickly. And can often read rather nicely.

roenxiOP7y ago

taeric7y ago

This actually takes it in a direction I disagree with.

Once you get used to manipulating buffers, elisp actually is easier than most other languages. What it is bad at is processing strings. Because it is good at processing text buffers.

That is, don't try and manipulate strings. Manipulate the entire buffer. If needed, build a new buffer with what all you want.

The irony is that elisp has a decent dsl for manipulating text. But you have to embrace the mutable nature of it. Which is unexpected for many working with a lisp.

kazinator7y ago

TXR Lisp is loaded with useful features, all packed into a small executable accompanied by a small library of Lisp files.

j / k navigate · click thread line to collapse