nrinaudo/kantan.regex

Regular expression library for Scala

Nicolas Rinaudo

@nrinaudo

On the other hand, you can use the decoding mechanism to yield two results, then manually conpose them into a tuple using flatmap

johannes karoff

@cornerman

@nrinaudo thanks for the response! how would i go about doing that? :)

Nicolas Rinaudo

@nrinaudo

sorry, missed your message.
So the principle is fairly straightforward - each evaluation yields an Either[Error, A], so you could write something like:

for {
  i <- str.evalRegex[Int](regex1)
  b <- str.evalRegex[Boolean](regex2)
} yield (i, b)

where regex1 and regex2 are the two regular expressions you with to compose and strthe string you wish to apply them to

@cornerman let me know if this isn't clear enough. If you were to give me a concrete use case, I could probably wip up some quick code to show you

johannes karoff

@cornerman

@nrinaudo ah got you. thats what you meant with decoding mechanism :)

my use-case is parsing a url-like structure. so I have a website, where i need to interpret the url (or more specifically the hash part of the url). so i have something similar to query parameters or key-value pairs like something=false&list=1,2,3&nothing=. so depending on the key, i need to interpret the rhs differently.

i was using fastparse previously to have a grammer for the options in the url. so i could write a parser for each option and then combine them in one grammar. that was nice. but is very slow on startup in scala.js.

johannes karoff

@cornerman

what i am doing now: i take the url and first match Map[String ->String] with a simple regex for k=v. and then i parse each entry in the map. so in the example, i would have then a regex for something, list and nothing.

so, it works now :)

johannes karoff

@cornerman

on another note: when i was using a star in my regex, e.g. (\w+)(:\d+)*. and then compiled a Regex[(String,String)] or Regex[(String,Seq[String])], I always got an error about an "empty group". I then went for (\w+)(:\d+)*? and used Regex[(String, Option[String])]. what can i do about this?

Nicolas Rinaudo

@nrinaudo

@cornerman Not sure about your use case for URI parsing, I would probably use a dedicated library for that as URI parameter parsing isn't as trivial as it might seem at first glance

johannes karoff

@cornerman

@nrinaudo in general i agree but it is not really a url. we have a SPA app running in the browser, which writes its current options to the hash-part of the url. the options are key-value pairs and similar to an url with regards to being a sequence of key-value pairs separated by & and =. so a dedicated uri parsing library would not really fit.

Nicolas Rinaudo

@nrinaudo

and as for your example, I'll need to see your code, because I don't think I understand what you're saying:

"abc:123".evalRegex[(String, String)](rx"(\w+)(:\d+)*").next
res1: kantan.regex.DecodeResult[(String, String)] = Right((abc,:123))

johannes karoff

@cornerman

yes, your example works, but if you have no match for (:\d+)*, it does not work:

"abc".evalRegex[(String, String)](rx"(\w+)(:\d+)*").next
res1: kantan.regex.DecodeResult[(String, String)] = Left(EmptyGroup: an empty group was found)

Nicolas Rinaudo

@nrinaudo

well yeah - the second group is not matched

so you get a match with a single group, which is what this is telling you

you have basically two choices there:

make the second group optional
make slightly more complicated groups (this would also allow you to ignore the :, which I'm assuming is desirable but I might be wrong)

johannes karoff

@cornerman

but semantically an empty string is a match for something* in a regex, isn't it?

Nicolas Rinaudo

@nrinaudo

you don't have an empty string. You have nothing

wait, what do you think the : means in your regex?

is that a separator, or did you think it means "non-capturing group"?

johannes karoff

@cornerman

no, just a separator

Nicolas Rinaudo

@nrinaudo

right

johannes karoff

@cornerman

i was under the impression, i could have a Regex[(String, Option[String])] from a *. just like from a ?. because both can yield an empty result

Nicolas Rinaudo

@nrinaudo

so then:

"abc:".evalRegex[(String, String)](rx"(\w+)(:\d*)").next

johannes karoff

@cornerman

but that is not what I want to match

Nicolas Rinaudo

@nrinaudo

but let's take it from the top. What are you precisely trying to do?

you can absolutely get an option from a * (I think), it's just that your regex requires : which your input doesn't contain

johannes karoff

@cornerman

oh, actually i really can!

sorry! it just works, i just made a mistake in my code :/

Nicolas Rinaudo

@nrinaudo

I understand what the first part of the regex is - you want a word as a key. The second part is more obscure. Do you require a :? If not but if it's present, can the \d sequence be empty?

oh, ok then

glad I could help, even if I'm not sure how!

johannes karoff

@cornerman

thank you for your time!

https://en.wikipedia.org/wiki/Rubber_duck_debugging :)

Stefan Endrullis

@xylo

In case that someone uses Intellij IDEA: I just added support for kantan.regex to my plugin called Custom Postfix Templates. It allows you to easily expand

"abc:".evalRegex

"abc:".evalRegex(rx"")

by automatically adding

import kantan.regex._
import kantan.regex.implicits._
import kantan.regex.generic._

to your imports.

Moreover,

"xyz".rx

is expanded to

rx"xyz"

also by adding the import.

Please let me know if I can improve these postfix templates.

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