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Some things I made to help my Clojure repl and you can too.


[com.gfredericks/repl-utils "0.2.22"]

The Good Parts


bg is a macro that is similar to future but with lots of repl-friendly features.

First a brief example:

user> (require '[ :refer [bg]])
user> (bg (Thread/sleep 2500) (inc 41))
Starting background task bg0
#<bg0 has been running for 0.003 seconds>
user> #<DONE: bg0 ran for 2.503 seconds>

user> bg0
user> (bg (/ 42 0))
Starting background task bg1
#<bg1 has been running for 0.000 seconds>#<ERROR(Divide by zero): bg1 ran for 0.000 seconds
user> >

user> bg1
#<java.lang.ArithmeticException@69b032 java.lang.ArithmeticException: Divide by zero>

The main idea is that bg is based on vars while future returns an IDeref. This means that instead of typing

user> (def f (future (inc 41)))
user> @f

you can type

user> (bg (inc 41))
Starting background task bg2
#<bg2 has been running for 0.001 seconds>#<DONE: bg2 ran for 0.001 seconds>
user> bg2

I.e., you get a name for free, and you don't have to use @/deref.

Minor Features

  • If an exception is thrown, the var will hold the exception instead of the result.
  • The var itself (i.e., the result of evaluating #'bg1) will print with state and timing info.
  • A message will be printed to *out* when the task finishes/errors.
  • You can access an actual future via (-> #'bg1 meta :future) in case you want to block on the result or whatever.
  • You can get the original form via (-> #'bg1 meta :form) in case you lose track of what you originally evaluated or something.
  • You can give the var a custom name via (bg some-name ...) if you find that useful.


A variant of clojure.walk/macroexpand-all that has fewer bugs and does not fully qualify symbols when possible (for the sake of better readability).

user> (require '[com.gfredericks.repl.mexpand :refer [mexpand-all]])
user> (mexpand-all '(fn [[x]] (identity x)))
   [vec__21034 p__21032 x (clojure.lang.RT/nth vec__21034 0 nil)]
   (identity x))))


Copyright © 2013 Gary Fredericks

Distributed under the Eclipse Public License, the same as Clojure.

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