Awesome
jl ![Build Status](https://travis-ci.org/chrisdone/jl.svg)
jl ("JSON lambda") is a tiny functional language for querying and manipulating JSON.
Example:
$ jl 'map $ \o -> { sha: o.sha, ps: map _.sha o.parents }' x.json
[{"sha":"7b81a836c31500e685d043729259affa8b670a87","ps":["c538237f4e4c381d35f1c15497c...
Installing
Binary releases for Linux and OS X are available here.
Builds on Windows (see AppVeyor status), haven't added Windows binaries to the releases yet.
Installing from source:
- Get stack
- Run
stack install
in the repository directory. - Add
~/.local/bin/
to yourPATH
.
Core syntax
Literals:
123, 4.5, -6, "hi", null, true, false
Lambdas:
\x -> y
Function application
get "f" o
Arithmetic:
x * (4 + 3)
Objects:
{foo: 123, bar: 34.3, "a:b": "hi"}
Arrays:
[1, 4 * 5, id 5]
Conditionals:
if x then y else z
Short-hand for fields:
o.f is sugar for get "f" o
_.f is sugar for (\o -> get "f" o)
For arrays:
_[0] is sugar for (\o -> get 0 o)
Or objects:
_[k] is sugar for (\o -> get k o)
_["foo"] is sugar for (\o -> get "foo" o)
Function composition:
a | b | c is sugar for `\x -> c (b (a x))`
Mini tutorial
You do everything with usual functional programming functions.
Returning the same thing, aka identity. That's normal in functional programming:
jl 'id'
A sequence of JSON strings will be read in and processed individually:
E.g.
$ cat x.json | jl id
{"a":1}
{"a":2}
{"a":3}
{"a":4}
If you want to read the input in as an array, use --array
:
$ cat x.json | jl --array 'map _.a'
[1,2,3,4]
After processing, sometimes you want to print each element of the
array out line by line, for that use --lines
:
$ cat x.json | jl --array --lines 'map _.a'
1
2
3
4
Taking the first element of something, using syntax that looks like
regular array access. The _
is a short-hand so that you don't need a
lambda:
jl '_[0]'
If you want to get what keys are available, you can run:
jl 'map keys | _[0]'
["sha","committer","url","comments_url","parents","author","html_url","commit"]
Taking the first element and then creating a record of some parts of it:
jl '_[0] | \o -> {msg: o.commit.message, n: o.commit.committer.name}'
Note the use of |
to compose functions. Just like in the shell.
Applying a function to all elements in an array:
jl 'map _.commit.committer.name'
Note how you can nest property access easily.
Applying something more detailed, by constructing a record of our own
jl 'map $ \o -> {msg: o.commit.message, n: o.commit.committer.name}'
You can use $
to avoid using parentheses on the right. That's a
trick from Haskell.
Applying functions to nested data structures:
jl '_[0] | \o -> {msg: o.commit.message, n: o.commit.committer.name, ps: map _.html_url o.parents }'
Notice the ps
property comes by taking the html_url
of all the parents.
Filtering is easy, simply write a function that returns true:
jl 'map (\o -> { sha: o.sha, ps: map _.sha o.parents }) | filter (\o -> length o.ps > 1)'
If you want to make an object with arbitrary keys that come at runtime, use set
:
$ echo '"hello"' | jl '\x -> set x 123 {}'
{"hello":123}
This sets the key x
in the empty object {}
to "hello"
with the value 123
.
You can use set
repeatedly to construct more keys.
If you want to construct an object from a list of key/values, you can use fold
:
$ echo '[{"k":"foo","v":123},{"k":"bar","v":456}]' | jl 'fold (\acc o -> set o.k o.v acc) {}'
{"foo":123,"bar":456}
Available functions
Record access
get :: JSON → JSON → JSON
Get the value at k from the object
set :: JSON → JSON → JSON → JSON
Set the value k to v in object
modify :: JSON → (JSON → JSON) → JSON → JSON
Modify the object at k with function f
keys :: JSON → JSON
Get all keys of the object
elems :: JSON → JSON
Get all elements of the object
Sequences
map :: (JSON → JSON) → JSON → JSON
Apply a function to every element in the sequence
filter :: (JSON → JSON) → JSON → JSON
Keep only items from the sequence for which p returns true
takeWhile :: (JSON → JSON) → JSON → JSON
Take elements from a sequence while given predicate is true
empty :: JSON → JSON
Is a sequence empty?
length :: JSON → JSON
Get the length of a sequence
reverse :: JSON → JSON
Reverse a sequence
drop :: JSON → JSON → JSON
Drop n items from the sequence
elem :: JSON → JSON → JSON
Is x an element of y?
concat :: JSON → JSON
Concatenate a list of sequences into one sequence
zipWith :: (JSON → JSON → JSON) → JSON → JSON → JSON
Zip two lists calling with each element to f x y
take :: JSON → JSON → JSON
Take n items from sequence
fold :: (JSON → JSON → JSON) → JSON → JSON → JSON
Fold over a structure with a state.
dropWhile :: (JSON → JSON) → JSON → JSON
Drop elements from a sequence while a predicate is true
any :: (JSON → JSON) → JSON → JSON
Does p return true for any of the elements?
all :: (JSON → JSON) → JSON → JSON
Does p return true for all of the elements?
nub :: JSON → JSON
Return the sequence with no duplicates; the nub of it
sort :: JSON → JSON
Return the sequence sorted
append :: JSON → JSON → JSON
Append the members of the second sequence to the first sequence
sum :: JSON → JSON
Get the sum of a sequence
product :: JSON → JSON
Get the product of a sequence
minimum :: JSON → JSON
Get the minimum of a sequence
maximum :: JSON → JSON
Get the maximum of a sequence
Strings
words :: JSON → JSON
Split the string into a list of words
unwords :: JSON → JSON
Join the list of strings into a string separated by spaces
lines :: JSON → JSON
Split the string into a list of lines
unlines :: JSON → JSON
Join the list of strings into a string separated by lines and terminated by a new line
Predicate operators
/= :: JSON → JSON → JSON
a /= b
= :: JSON → JSON → JSON
a = b
Boolean operators
&& :: JSON → JSON → JSON
a && b
|| :: JSON → JSON → JSON
a || b
not :: JSON → JSON
not b
Numeric operators
> :: JSON → JSON → JSON
a > b
< :: JSON → JSON → JSON
a < b
>= :: JSON → JSON → JSON
a >= b
<= :: JSON → JSON → JSON
a <= b
* :: JSON → JSON → JSON
a * b
+ :: JSON → JSON → JSON
a + b
- :: JSON → JSON → JSON
a - b
/ :: JSON → JSON → JSON
a / b
min :: JSON → JSON → JSON
a min b
max :: JSON → JSON → JSON
a max b
abs :: JSON → JSON
abs b
Function combinators
id :: JSON → JSON
Identity function, returns its input unchanged
compose :: (JSON → JSON) → (JSON → JSON) → JSON → JSON
Compose two functions
flip :: (JSON → JSON → JSON) → JSON → JSON → JSON
Flips the argument order of a function of two or more arguments