Joker is a small Clojure interpreter and linter written in Go.
On macOS, the easiest way to install Joker is via Homebrew:
brew install candid82/brew/joker
The same command can be used on Linux if you use Linuxbrew.
If you use Arch Linux, there is AUR package.
If you use Nix, then you can install Joker with
nix-env -i joker
On other platforms (or if you prefer manual installation), download a precompiled binary for your platform and put it on your PATH.
You can also build Joker from the source code.
joker
- launch REPL
joker <filename>
- execute a script. Joker uses .joke
filename extension. For example: joker foo.joke
. Normally exits after executing the script, unless --exit-to-repl
is specified before --file <filename>
in which case drops into the REPL after the script is (successfully) executed. (Note use of --file
in this case, to ensure <filename>
is not treated as a <socket>
specification for the repl.)
joker --eval <expression>
- execute an expression. For example: joker -e '(println "Hello, world!")'
. Normally exits after executing the script, unless --exit-to-repl
is specified before --eval
,
in which case drops into the REPL after the expression is (successfully) executed.
joker --lint <filename>
- lint a source file. See Linter mode for more details.
joker --lint --working-dir <dirname>
- recursively lint all Clojure files in a directory.
joker -
- execute a script on standard input (os.Stdin).
Organizing Libraries (Namespaces)
These are high level goals of the project that guide design and implementation decisions.
- Be suitable for scripting (lightweight, fast startup). This is something that Clojure is not good at and my personal itch I am trying to scratch.
- Be user friendly. Good error messages and stack traces are absolutely critical for programmer's happiness and productivity.
- Provide some tooling for Clojure and its dialects. Joker has linter mode which can be used for linting Joker, Clojure and ClojureScript code. It catches some basic errors. Joker can also be used for pretty printing EDN data structures (very basic algorithm at the moment). For example, the following command can be used to pretty print EDN data structure (read from stdin):
joker --hashmap-threshold -1 -e "(pprint (read))"
There is Sublime Text plugin that uses Joker for pretty printing EDN files. Here you can find the description of --hashmap-threshold
parameter, if curious. Tooling is one of the primary Joker use cases for me, so I intend to improve and expand it.
- Be as close (syntactically and semantically) to Clojure as possible. Joker should truly be a dialect of Clojure, not a language inspired by Clojure. That said, there is a lot of Clojure features that Joker doesn't and will never have. Being close to Clojure only applies to features that Joker does have.
- Performance. If you need it, use Clojure. Joker is a naive implementation of an interpreter that evaluates unoptimized AST directly. I may be interested in doing some basic optimizations but this is definitely not a priority.
- Have all Clojure features. Some features are impossible to implement due to a different host language (Go vs Java), others I don't find that important for the use cases I have in mind for Joker. But generally Clojure is a pretty large language at this point and it is simply unfeasible to reach feature parity with it, even with naive implementation.
- Primitive types are different due to a different host language and desire to simplify things. Scripting doesn't normally require all the integer and float types, for example. Here is a list of Joker's primitive types:
Joker type | Corresponding Go type |
---|---|
BigFloat | big.Float |
BigInt | big.Int |
Boolean | bool |
Char | rune |
Double | float64 |
Int | int |
Keyword | n/a |
Nil | n/a |
Ratio | big.Rat |
Regex | regexp.Regexp |
String | string |
Symbol | n/a |
Time | time.Time |
Note that Nil
is a type that has one value nil
.
- The set of persistent data structures is much smaller:
Joker type | Corresponding Clojure type |
---|---|
ArrayMap | PersistentArrayMap |
MapSet | PersistentHashSet (or hypothetical PersistentArraySet, depending on which kind of underlying map is used) |
HashMap | PersistentHashMap |
List | PersistentList |
Vector | PersistentVector |
- Joker doesn't have the same level of interoperability with the host language (Go) as Clojure does with Java or ClojureScript does with JavaScript. It doesn't have access to arbitrary Go types and functions. There is only a small fixed set of built-in types and interfaces. Dot notation for calling methods is not supported (as there are no methods). All Java/JVM specific functionality of Clojure is not implemented for obvious reasons.
- Joker is single-threaded with no support for parallelism. Therefore no refs, agents, futures, promises, locks, volatiles, transactions,
p*
functions that use multiple threads. Vars always have just one "root" binding. Joker does have core.async style support for concurrency. Seego
macro documentation for details. - The following features are not implemented: protocols, records, structmaps, chunked seqs, transients, tagged literals, unchecked arithmetics, primitive arrays, custom data readers, transducers, validators and watch functions for vars and atoms, hierarchies, sorted maps and sets.
- Unrelated to the features listed above, the following function from clojure.core namespace are not currently implemented but will probably be implemented in some form in the future:
subseq
,iterator-seq
,reduced?
,reduced
,mix-collection-hash
,definline
,re-groups
,hash-ordered-coll
,enumeration-seq
,compare-and-set!
,rationalize
,load-reader
,find-keyword
,comparator
,resultset-seq
,file-seq
,sorted?
,ensure-reduced
,rsubseq
,pr-on
,seque
,alter-var-root
,hash-unordered-coll
,re-matcher
,unreduced
. - Built-in namespaces have
joker
prefix. The core namespace is calledjoker.core
. Other built-in namespaces includejoker.string
,joker.json
,joker.os
,joker.base64
etc. See standard library reference for details. - Joker doesn't support AOT compilation and
(-main)
entry point as Clojure does. It simply reads s-expressions from the file and executes them sequentially. If you want some code to be executed only if the file it's in is passed asjoker
argument but not if it's loaded from other files, use(when (= *main-file* *file*) ...)
idiom. See candid82#277 for details. - Miscellaneous:
case
is just a syntactic sugar on top ofcondp
and doesn't require options to be constants. It scans all the options sequentially.slurp
only takes one argument - a filename (string). No options are supported.ifn?
is calledcallable?
- Map entry is represented as a two-element vector.
- resolving unbound var returns
nil
, not the valueUnbound
. You can still check if the var is bound withbound?
function.
To run Joker in linter mode pass --lint --dialect <dialect>
flag, where <dialect>
can be clj
, cljs
, joker
or edn
. If --dialect <dialect>
is omitted, it will be set based on file extension. For example, joker --lint foo.clj
will run linter for the file foo.clj
using Clojure (as opposed to ClojureScript or Joker) dialect. joker --lint --dialect cljs -
will run linter for standard input using ClojureScript dialect. Linter will read and parse all forms in the provided file (or read them from standard input) and output errors and warnings (if any) to standard output (for edn
dialect it will only run read phase and won't parse anything). Let's say you have file test.clj
with the following content:
(let [a 1])
Executing the following command joker --lint test.clj
will produce the following output:
test.clj:1:1: Parse warning: let form with empty body
The output format is as follows: <filename>:<line>:<column>: <issue type>: <message>
, where <issue type>
can be Read error
, Parse error
, Parse warning
or Exception
.
- Emacs: flycheck syntax checker
- Sublime Text: SublimeLinter plugin
- Atom: linter-joker
- Vim: syntastic-joker, ale
- VSCode: VSCode Linter Plugin (alpha)
- Kakoune: clj-kakoune-joker
Here are some examples of errors and warnings that the linter can output.
Joker lints the code in one file at a time and doesn't try to resolve symbols from external namespaces. Because of that and since it's missing some Clojure(Script) features it doesn't always provide accurate linting. In general it tries to be unobtrusive and error on the side of false negatives rather than false positives. One common scenario that can lead to false positives is resolving symbols inside a macro. Consider the example below:
(ns foo (:require [bar :refer [def-something]]))
(def-something baz ...)
Symbol baz
is introduced inside def-something
macro. The code is totally valid. However, the linter will output the following error: Parse error: Unable to resolve symbol: baz
. This is because by default the linter assumes external vars (bar/def-something
in this case) to hold functions, not macros. The good news is that you can tell Joker that bar/def-something
is a macro and thus suppress the error message. To do that you need to add bar/def-something
to the list of known macros in Joker configuration file. The configuration file is called .joker
and should be in the same directory as the target file, or in its parent directory, or in its parent's parent directory etc up to the root directory. When reading from stdin Joker will look for a .joker
file in the current working directory. The --working-dir <path/to/file>
flag can be used to override the working directory that Joker starts looking in. Joker will also look for a .joker
file in your home directory if it cannot find it in the above directories. The file should contain a single map with :known-macros
key:
{:known-macros [bar/def-something foo/another-macro ...]}
Please note that the symbols are namespace qualified and unquoted. Also, Joker knows about some commonly used macros (outside of clojure.core
namespace) like clojure.test/deftest
or clojure.core.async/go-loop
, so you won't have to add those to your config file.
Joker also allows you to specify symbols that are introduced by a macro:
{:known-macros [[riemann.streams/where [service event]]]}
So each element in :known-macros vector can be either a symbol (as in the previous example) or a vector with two elements: macro's name and a list of symbols introduced by this macro. This allows to avoid symbol resolution warnings in macros that intern specific symbols implicitly.
Additionally, if you want Joker to ignore some unused namespaces (for example, if they are required for their side effects) you can add the :ignored-unused-namespaces
key to your .joker
file:
{:ignored-unused-namespaces [foo.bar.baz]}
Sometimes your code may refer to a namespace that is not explicitly required in the same file. This is rarely needed, but if you face such situation you can add that namespace to :known-namespaces
list to avoid "No namespace found" or "Unable to resolve symbol" warnings:
{:known-namespaces [clojure.spec.gen.test]}
If your code uses tagged literals that Joker doesn't know about, add them to :known-tags
list:
{:known-tags [db/fn]}
If you use :refer :all
Joker won't be able to properly resolve symbols because it doesn't know what vars are declared in the required namespace (i.e. clojure.test
). There are generally three options here:
- Refer specific symbols. For example:
[clojure.test :refer [deftest testing is are]]
. This is usually not too tedious, and you only need to do it once per file. - Use alias and qualified symbols:
(:require [clojure.test :as t])
(t/deftest ...)
-
"Teach" Joker declarations from referred namespace. Joker executes the following files (if they exist) before linting your file:
.jokerd/linter.cljc
(for both Clojure and ClojureScript),.jokerd/linter.clj
(Clojure only),.jokerd/linter.cljs
(ClojureScript only). The rules for locating.jokerd
directory are the same as for locating.joker
file.โ ๏ธ Joker can be made aware of any additional declarations (likedeftest
andis
) by providing them in.jokerd/linter.clj[s|c]
files. However, this means Joker cannot check that the symbols really are declared in your namespace, so this feature should be used sparingly.- If you really want some symbols to be considered declared in any namespace no matter what, you can add
(in-ns 'joker.core)
to yourlinter.clj[s|c]
and then declare those symbols. (see issues 52 and 50 for discussion).
I generally prefer first option for clojure.test
namespace.
To recursively lint all files in a directory pass --working-dir <dirname>
parameter. Please note that if you also pass file argument (or --file
parameter) Joker will lint that single file and will only use --working-dir
to locate .joker
config file. That is,
joker --lint --working-dir my-project
lints all Clojure files in my-project
directory, whereas
joker --lint --working-dir my-project foo.clj
lints single file foo.clj
but uses .joker
config file from my-project
directory.
When linting directories Joker lints all files with the extension corresponding to the selected dialect (*.clj
, *.cljs
, *.joke
, or *.edn
). To exclude certain files specify regex patterns in :ignored-file-regexes
vector in .joker
file, e.g. :ignored-file-regexes [#".*user\.clj" #".*/dev/profiling\.clj"]
.
When linting directories Joker can report globally unused namespaces and public vars. This is turned off by default but can be enabled with --report-globally-unused
flag, e.g. joker --lint --working-dir my-project --report-globally-unused
. This is useful for finding "dead" code. Some namespaces or vars are intended to be used by external systems (e.g. public API of a library or main function of a program). To exclude such namespaces and vars from being reported as globally unused list them in :entry-points
vector in .joker
file, which may contain the names of namespaces or fully qualified names of vars. For example:
:entry-points [my-project.public-api
my-project.core/-main]
Joker supports a few configurable linting rules. To turn them on or off set their values to true
or false
in :rules
map in .joker
file. For example:
:rules {:if-without-else true
:no-forms-threading false}
Below is the list of all configurable rules.
Rule | Description | Default value |
---|---|---|
if-without-else |
warn on if without the else branch |
false |
no-forms-threading |
warn on threading macros with no forms, i.e. (-> a) |
true |
unused-as |
warn on unused :as binding |
true |
unused-keys |
warn on unused :keys , :strs , and :syms bindings |
true |
unused-fn-parameters |
warn on unused fn parameters | false |
fn-with-empty-body |
warn on fn form with empty body | true |
Note that unused binding
and unused parameter
warnings are suppressed for names starting with underscore.
Joker requires Go v1.13 or later. Below commands should get you up and running.
go get -d github.com/candid82/joker
cd $GOPATH/src/github.com/candid82/joker
./run.sh --version && go install
After building the native version (to autogenerate appropriate files, "vet" the source code, etc.), set the appropriate environment variables and invoke go build
. E.g.:
$ GOOS=linux GOARCH=arm GOARM=6 go build
(The run.sh
script does not support cross-platform building.)
- Dashes (
-
) in namespaces are not converted to underscores (_
) by Joker, so (unlike with Clojure) there's no need to name.joke
files accordingly. - Avoid
:refer :all
and theuse
function, as that reduces the effectiveness of linting.
See DEVELOPER.md
for information on Joker internals, such as adding new namespaces to the Joker executable.
(Generated by Hall-Of-Fame)
Copyright (c) Roman Bataev. All rights reserved.
The use and distribution terms for this software are covered by the
Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
which can be found in the LICENSE file.
Joker contains parts of Clojure source code (from clojure.core
namespace). Clojure is licensed as follows:
Copyright (c) Rich Hickey. All rights reserved.
The use and distribution terms for this software are covered by the
Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
which can be found in the file epl-v10.html at the root of this distribution.
By using this software in any fashion, you are agreeing to be bound by
the terms of this license.
You must not remove this notice, or any other, from this software.