@richiardiandrea: http://clojure.org/reference/reader

@codonnell: thanks!

no problem

mattly: fwiw I needed that once and never found a library, just ended up writing a function to generate query params manually

can someone help me with my regex issues? I’m trying to extract out everything within square brackets into capture groups:

"hello" -> (“hello”)
“hello there” -> (“hello there”)
“hello there [foo,bar]” -> (“hello there” “foo” “bar”)

java’s posessive quantifiers are not working like I expect them to

@jethroksy: what do you currently have?

#"(.*)\s+?(\[.*\])?”

right now I’m just concerning myself with separating the stuff in brackets from the stuff that aren't

this doesn’t work for the first case: ”hello” -> (“hello”)

yeah, \s+? means one or more whitespace

initially I wanted to make (\[.*\])?+ possessive

but I don’t think the X?+ syntax is allowed here

it sounds like you want everything before [

yup

([^\[]+)\[

though you might not have the [

right, but the square brackets are optional

May I ping you again later if I have any problems?

sure

Thanks!

hi

despite the documentation on lein-migratus, i don’t seem to be able to understand what it does

the only times i’ve gotten it to work is by deleting my old tables, then running $ lein migratus

but a migration should keep my data and just change the schema, right?

i don’t see any changes in my postgresql columns, so im confused

are you putting changes in a new file every time you run migratus?

I am trying to load a bunch of files in a folder while in a jar. I found this: http://stackoverflow.com/questions/11012819/how-can-i-get-a-resource-folder-from-inside-my-jar-file

They do this though:

final File jarFile = new File(getClass().getProtectionDomain().getCodeSource().getLocation().getPath());

How to I call getClass() from Clojure? I assume it implicitly hits a class but which one?

Basically i am missing a reference to “this” in Clojure, which is implicit in the above

that snippet is running inside some class

you just need to choose a class from the jar explicitly

(.getProtectionDomain MyClass)

Anyone here using aleph/manifold in production for web servers? any comments on performance compared to the usual compojure/jetty/ring stack one would get with (for example) Luminus?

@shanekilkelly: you may be interested in #C0702A7SB also

@nha, indeed, meant to mention yada in the post above i’ve been looking at yada/bidi/aleph/manifold recently and would be curious to hear from anyone who has deployed a similar stack in production.

I’m most interested in high-performance and massively concurrent clojure network servers, think the kind of thing Go or Node.js are commonly used for.

what's the fastest way to concatenate 2 vectors ?

What comes to mind for me is (reduce conj v1 v2)

blackblock: http://stackoverflow.com/a/2710597/1685746

@rm I meant the fastest way performance-wise

performance-wise you don't want to concat two vectors

@codonnell: (into x y) would use transients

Sorry, I meant @octo221

@rauh: nice, that is a better solution

Does anyone know of a ring middleware to handle a file upload, where the file is in the body of the request itself; i.e. it's not multipart form encoded? I need it to also buffer into a tempfile; or at least not load the body into memory, because it may be several GBs

@rm yes, that's why I'm asking!

@rauh: thanks, that's what I wanted to know

@rauh exactly what I needed to know

@octo221: you can use into

oh, you got it

nvm

What's the correct way to ask whether a var exists for a given symbol?

resolve for the current ns, or ns-resolve with the ns as argument

Ah, perfect, thanks

hey @rickmoynihan: by what means is your upload occurring- not through a file button on a web page? file uploads are included in request bodies; the multi-part form encoding is the format of the request body data.

@jonahbenton: it's for an API - not a web form... not actually tried it yet but yeah it looks like ring just puts an inputstream in the :body for you - which is fine

What is ^ symbol in Clojure? Example:

(defn get-elmt [activity elmt]
  (str (.getText ^TextView (find-view activity elmt))))

http://clojure.org/reference/reader#_metadata

@liathit and http://clojure.org/reference/java_interop#typehints

hiredman: crucialrhyme thx 😉

I'm using duct with a reloaded workflow. Everything was working great until I did a windows update and restarted my computer. Now when I attempt to start my system I get an exception

duct.component.handler.Handler cannot be cast to clojure.lang.IFn

http://xahlee.info/clojure/clojure_metadata.html

jjttjj: the full stacktrace will have more information about what line the error occurs on, but somewhere you have an instance of Handler that you are trying to invoke as a function

More of an opinion, but which do you feel is a better signature for an API that calls an underlying Java API with 3 different overloads, each with drastically different behavior (yes, the underlying api is badly designed). Bear in mind that this will be adapted to work on a protocol:

I personally feel the cond is a bit of an anti-pattern in a lot of cases, but there's a few libraries I've found doing similar things to support/prefer passing maps as args

I think it would depend on how drastically different the behavior is

are you talking the difference between a pure function and something with side effects?

they return the same result type, but consume different parts of an iterator

so essentially they filter out results from an iterator

If it were up to me, I wouldn't do that at all, but it isn't my lib

we already have functions in clojure.core that are like a partial application when called with a lower arity

not sure if it’s anything like that

no, I guess not

nope , but looking to clojure.core is always where I start

you said they all have the same return type but do different things with the iterator

yup, that's right

can you think of a single function name that describes all three implementations accurately?

well a comment will suffice and keep it close to the original api if I just use a 3 arity definition on a protocol

if you’re never going to call it with apply or anything like that I would just use differently-named functions

also this may be getting called a few thousand/100k times a second

so I would think using apply would just slow you down considering this is for high performance

also the dispatch for 3-arity is a bit more efficient considering they each call a distinct java overload

just a bit of duplicated conversions in 2 of the arities I think

but 1 extra line of code shared between the 2, no big deal and probably the way to go for performance

the body probably dominates the invocation. don't forget to measure

yup, will do

on that subject, is there a significant overhead instantiating a collection of records vs maps, assuming the record is just a container, and probably the result set is immediately going to have 1-3 lookups on top-level keys?

assuming you'd be getting back say, anywhere between as little as a few, and as much as a few thousand per collection

Are toplevel do blocks special to the Clojure compiler? It seems to confuse cloverage, and I could see how the compiler just elides them...

I would expect a more compact memory footprint for the records, but maybe other penalties I haven't thought about

hugesandwich: you should measure if you really care. Small maps are the most efficient because of PersistentArrayMap

it's just a flat array

@ghadi Yeah, planned to for sure, I always try to measure, but thought I'd ask if it's stupid to even waste the time

maps are really complicated unfortunately, so many factors

kind of hard to know because it depends heavily on the data volume of api users

size of maps, lookup patterns, etc.

and I can mess with batch sizes to further complicate things

lvh: they are, the compiler treats each expression in a top level do as a top level form

well, that gives me somewhat of a hint why cloverage balks

OK, I think I found it: https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Compiler.java#L6001-L6003

That doesn’t really explain why cloverage is ok with (do 1)

(maybe it isn’t?)

I think I’ve asked this before, but can anyone remind me why (#()) evals to ()?

is cloveraged used a lot?

@chancerussell: (macroexpand '#()) -> (fn* [] ())

and (type ()) -> clojure.lang.PersistentList$EmptyList

looks like clojure doesn't eval the form if its empty

That would explain it Thanks @mtkp

is it bad programming to have a lazyseq perform side effects to construct itself as it's read?

i'm scanning rows on a remote db

java.jdbc does exactly that

but you have to do it in the context of an open ResultSet

well I was going to write code using clojure's lazyseq macro that does net IO

maybe lazyseq / ISeq isn't expressive enough as ResultSet for this sort of thing

have I got a dated write up you

http://ce2144dc-f7c9-4f54-8fb6-7321a4c318db.s3.amazonaws.com/reducers.html

hiredman: sorry just scanned the text, that looks ok if i want to materialize the whole result set in memory, or aggregate the whole result set, but there's no reduction in my work, I'm doing db in -> map -> db out

i want to transfer contents between databases in small batches

need logic for retries, or missing records

so i'll just write stupid for loop i guess

you should read it more carefully then, it is entirely about reducible collections being a better way to represent resources as collections that you don't want to be entirely in memory at once

k, taking a second look

db out -> map -> db out is reduce

(reduce  (fn [db row] (insert db (f row)))  db (query db)) 

the write up is dated, because 1.8 and 1.7 brought new useful reduce and transduce stuff, which you could use to improve in various ways what is in the write up, but what is in the write still works great, and is an improvement over representing resources as seqs

sweet, hmh, yah this is making more sense

half way through the article

hiredman: nice yah i'm going to start implementing this, i guess i lucked out you had a write-up to my exact question 😉

the only thing the abstraction doesn't necessarily handle gracefully, is the lifecycle of the db out

if i'm reducing db in, I can have coll-reduce easily manage the lifecycle of the db connection

you might want to look at the new clojure.lang.IReduce and IReduceInit interfaces (I think added in 1.8) instead of implementing the CollReduce protocol

for db out, i'll just reopen the connection each time, no big deal

will check that out

transduce lets you provide a reducing function with 3 arities, with which you can do something like

(fn ([] (open-db-connection)) ([conn] (close-db-connection conn)) ([conn value] ...))

but that isn't the same as a close in a finally, so it can be tricky

hmhm ok, i'll check that out too

hiredman: "When to use Use the reducer form of these operations when: Source data can be generated and held in memory Work to be performed is computation (not I/O or blocking) Number of data items or work to be done is "large""

http://clojure.org/reference/reducers

that is nonsense

that reads like the kind of restrictions you would put on the reducers concept of "fold" because of the way it does parallel computation

if you look at http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html (linked from the write up) under the heading "More Opportunity (i.e. Work)" rhickey explicitly called it out as a mechanism for solving "the lazily dangling open resource problem"