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https://github.com/chrisdone/jl

Functional sed for JSON
https://github.com/chrisdone/jl

command-line command-line-tool haskell json

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Functional sed for JSON

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# jl [![Build Status](https://travis-ci.org/chrisdone/jl.svg)](https://travis-ci.org/chrisdone/jl)

jl ("JSON lambda") is a tiny functional language for querying and

manipulating JSON.



Example:



``` haskell

$ 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](https://github.com/chrisdone/jl/releases).



Builds on Windows (see [AppVeyor status](https://ci.appveyor.com/project/chrisdone/jl)), haven't added Windows

binaries to the releases yet.



Installing from source:



1. Get [stack](https://haskell-lang.org/get-started)

2. Run `stack install` in the repository directory.

3. Add `~/.local/bin/` to your `PATH`.



## 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:



``` haskell

jl 'id'

```



A sequence of JSON strings will be read in and processed individually:



E.g.



``` haskell

$ 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`:



``` haskell

$ 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`:



``` haskell

$ 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:



``` haskell

jl '_[0]'

```



If you want to get what keys are available, you can run:



``` haskell

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:



``` haskell

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:



``` haskell

jl 'map _.commit.committer.name'

```



Note how you can nest property access easily.



Applying something more detailed, by constructing a record of our own



``` haskell

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:



``` haskell

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:



``` haskell

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`:



``` haskell

$ 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`:



```haskell

$ 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



```haskell

get :: JSON → JSON → JSON

```



Get the value at k from the object



```haskell

set :: JSON → JSON → JSON → JSON

```



Set the value k to v in object



```haskell

modify :: JSON → (JSON → JSON) → JSON → JSON

```



Modify the object at k with function f



```haskell

keys :: JSON → JSON

```



Get all keys of the object



```haskell

elems :: JSON → JSON

```



Get all elements of the object



## Sequences



```haskell

map :: (JSON → JSON) → JSON → JSON

```



Apply a function to every element in the sequence



```haskell

filter :: (JSON → JSON) → JSON → JSON

```



Keep only items from the sequence for which p returns true



```haskell

takeWhile :: (JSON → JSON) → JSON → JSON

```



Take elements from a sequence while given predicate is true



```haskell

empty :: JSON → JSON

```



Is a sequence empty?



```haskell

length :: JSON → JSON

```



Get the length of a sequence



```haskell

reverse :: JSON → JSON

```



Reverse a sequence



```haskell

drop :: JSON → JSON → JSON

```



Drop n items from the sequence



```haskell

elem :: JSON → JSON → JSON

```



Is x an element of y?



```haskell

concat :: JSON → JSON

```



Concatenate a list of sequences into one sequence



```haskell

zipWith :: (JSON → JSON → JSON) → JSON → JSON → JSON

```



Zip two lists calling with each element to f x y



```haskell

take :: JSON → JSON → JSON

```



Take n items from sequence



```haskell

fold :: (JSON → JSON → JSON) → JSON → JSON → JSON

```



Fold over a structure with a state.



```haskell

dropWhile :: (JSON → JSON) → JSON → JSON

```



Drop elements from a sequence while a predicate is true



```haskell

any :: (JSON → JSON) → JSON → JSON

```



Does p return true for any of the elements?



```haskell

all :: (JSON → JSON) → JSON → JSON

```



Does p return true for all of the elements?



```haskell

nub :: JSON → JSON

```



Return the sequence with no duplicates; the nub of it



```haskell

sort :: JSON → JSON

```



Return the sequence sorted



```haskell

append :: JSON → JSON → JSON

```



Append the members of the second sequence to the first sequence



```haskell

sum :: JSON → JSON

```



Get the sum of a sequence



```haskell

product :: JSON → JSON

```



Get the product of a sequence



```haskell

minimum :: JSON → JSON

```



Get the minimum of a sequence



```haskell

maximum :: JSON → JSON

```



Get the maximum of a sequence



## Strings



```haskell

words :: JSON → JSON

```



Split the string into a list of words



```haskell

unwords :: JSON → JSON

```



Join the list of strings into a string separated by spaces



```haskell

lines :: JSON → JSON

```



Split the string into a list of lines



```haskell

unlines :: JSON → JSON

```



Join the list of strings into a string separated by lines and terminated by a new line



## Predicate operators



```haskell

/= :: JSON → JSON → JSON

```



a /= b



```haskell

= :: JSON → JSON → JSON

```



a = b



## Boolean operators



```haskell

&& :: JSON → JSON → JSON

```



a && b



```haskell

|| :: JSON → JSON → JSON

```



a || b



```haskell

not :: JSON → JSON

```



not b



## Numeric operators



```haskell

> :: JSON → JSON → JSON

```



a > b



```haskell

< :: JSON → JSON → JSON

```



a < b



```haskell

>= :: JSON → JSON → JSON

```



a >= b



```haskell

<= :: JSON → JSON → JSON

```



a <= b



```haskell

* :: JSON → JSON → JSON

```



a * b



```haskell

+ :: JSON → JSON → JSON

```



a + b



```haskell

- :: JSON → JSON → JSON

```



a - b



```haskell

/ :: JSON → JSON → JSON

```



a / b



```haskell

min :: JSON → JSON → JSON

```



a min b



```haskell

max :: JSON → JSON → JSON

```



a max b



```haskell

abs :: JSON → JSON

```



abs b



## Function combinators



```haskell

id :: JSON → JSON

```



Identity function, returns its input unchanged



```haskell

compose :: (JSON → JSON) → (JSON → JSON) → JSON → JSON

```



Compose two functions



```haskell

flip :: (JSON → JSON → JSON) → JSON → JSON → JSON

```



Flips the argument order of a function of two or more arguments