Janiva

Janiva programming language, inspired & bootstrapped by Simple Language

Build Project

Generate parser

./generate_parser.sh

Set JAVA_HOME

Set JAVA_HOME to a graalvm installation path (22.30, jdk17 is preferred)

Run unit tests

mvn clean test

Janiva is an extension of JSON. It enhances json by providing the capability of doing arithmetics, functional programming, and control flows

Terminologies

Data flow

Data flow is represented by << operator. Is is used for

• transfer output to stdout
• latent attribute binding

Primitive

Janiva primitives are

• number
• string
• boolean

a primitive itself is a Janiva program

Object

Object composes of attributes where keys are strings and values are

• primitives
• objects
• lists

List

List is a collections of values

Value

Value can be primitives, objects or lists

Attribute

Contents of objects are attributes for example, the root object has two attributes a and b

{
    "a": 1,
    "b": 2
}

Attribute binding

Attribute binding is an operation that binds a value to an attribute in current context

{
  "a": 1
}

Latent attribute binding

Attributes that are excluded from the final json output are called latent attributes. To define a latent attribute, simple use << operator

{
    "a": 1,
    // Here we bind b to 2
    b << 2,
    "e": {
      // b is bound in child scope
      b << 3,
      "c": 3
    }
}

Attribute reference

A attribute or latent attribute can be referred to and bound to another attribute. Attribute references are performed by $ operator, for example

{
    "a": 1,
    // Here we bind b to 2
    b << 2,

    // The attribute c is bound by referring to latent attribute b
    "c": $b,
    "d": {
        // looks up b in parent scope
        "c": $b,
    },
    "e": {
      // b is bound in child scope, thus "c" here is bound to 3
      b << 3,
      "c": $b
    }
}

Std out

To make Janiva usable, it is able to feed interpreted json to output, simple using << operator

@stdout << {
  "a": 1,
  "b": 2.5,
  "c": {
    "d": [1+1, "a" + 2]
  }
}

Internally, stdout performs like a built-in lambda that flush the object to std out and return a reference to original object.

lambda

lambdas are pure functions declared at the beginning of the script. Definitions of lambdas start with @ and end with #. @ is also used to refer to a lambda instance.

lambda can be applied by feeding data to it using << operator. Note that partial evaluation is not supported, therefore parameter list must match in length.

// Define two lambdas

// adding two numbers
@add :: (x, y) >> $x + $y #

// converting a tuple to object
@tuple_to_dict :: (x, y) >> {"first": $x, "second": $y} #

stdout << {
    // binding sum of two numbers to a
    "a": @add << 1 << 2,
    // binding a dict to latent attribute _tuple
    _tuple << @tuple_to_dict << 1 << 2,
    // refer to latent attribute
    "tuple": $_tuple,
}

Partial application

Janiva supports partial application of lambdas, which mean you don't have to provide all arguments once, instead, you can feed a part of arguments, and provide the rest later. For example

// Here we defined a lambda which takes 5 numbers as argument
@add5 :: (x1, x2, x3, x4, x5) >> $x1 + $x2 + $x3 + $x4 + $x5 #

@stdout << {
    // partial apply with two of them
    _x12 << @add5 << 1 << 1,
    // note that _x12 is a lambda that takes 3 numbers and add then to (1 + 1)
    "sum1": @_x12 << 1 << 1 << 1,
    // Everytime a partially applied lambda is called, a light copy was made to ensure immutability
    "sum2": @_x12 << 2 << 2 << 2,
}

Control flow

There's no control flow in Janiva, instead, it provides couple of built-in functions that do the similar job.

If

If takes three arguments

• condition that evaluates to a boolean
• then value when condition is true
• else value when condition is false

for example

stdout << {
    "a": @if << true << 1 << 2,
    "b": @if << false << 1 << 2,
}

Range

Range can take three types of arguments

• If a integer N is given, it returns a integer array [0, ... N-1]
• If a string is given, it simply split the string into chars, for example "hello" >> ["h", "e", "l", "l", "o"]
• If an array is given, it returns a reference to that array. Note that arrays are immutable, thus no copy is required

Import and Export

Imports and exports looks exactly like lambdas, which are denoted by @import and @export, however, not like @export, @import is a primitive instead of lambda. The reason why @import can't be a lambda is that it needs to eccess another code file and evaluate it. This cannot be done using lambda, because lambda is a run-time role, which only participates with guest language objects, and it is difficult to insert new nodes to ast during run-time. Therefore, @import is designed to take effect during static analysis.

Export

@export is a lambda that takes an object as argument, just like @stdout

@export << {
    "a": 1
}

It marks an object as exported.

Import

Import is not l lambda but it follows the same syntax. Imports are treated like pre-processors, which are executed at the very beginning of the program.

_value << @import << "ex.ut-export" #

@stdout << {
    "k": {"c": "d"},
    // Refer to imported value
    "value": $_value
}

Note that a value must be exported to be imported by other codes.