ZVINT

ZVINT (ZLS Value Interpreter) is a simple code parser for simple string statements. This is intended for use with JSON properties where we can put meaning to value rather than raw type values.

value1 ?: value2

can be interpreted when given a context of

value1 = null
value2 = "hello"

to get return value of

hello

where value1 ?: value2 meaning 'if value1 is null then get value2 else get value1'.

This feature can be used to implement get meaningful JSON. for example.

  {
    "cakeWeight": "10",
    "isEnough": "$ cakeWeight == 10"
  }

Parsing the above property "isEnough" with context cakeWeight = 10 to get "isEnough" = true.

Known Issues

refer gitlab issue tracker

Syntax Available

String:

While evaluating as a string you should put ' & ' to indicate a string.

    'this is a string'
    'thisstring'

Variables:

Simple variables that represent the context name like

    myvar
    test.status
    array[10]

for the array to work the context must have a map with key array and its value as array of string values.

Boolean

Basic boolean values

    true
    false

Null

Only the string literal 'null' is interpreted as a null value

Operators & Conditionals

a handset of conditionals are acceptable

    a == b // a equals b
    v != a // v not equals a
    b ?: 'c' // if b is 'null' then return a string c

Complex (Brackets)

It is also possible to use brackets around simple statements that needs to be evaluated.

    (a == b)
    ((a != b) && (b != c))      // No tests have been written yet, but this should work

This is only in experimental state and recursive statements like the second one may not work.

Functions:

    'helloApi'(a, '10')

'helloApi' is interpreted literally. Which means that zvint will try to search for 'helloApi' inside the eval function. a and '10' are passed as arguments to the eval function.

If you want the function name to be evaluated before being called then you can do

    myVar(a, '10')

Here, myVar is first evaluated from either the Context's pool map or eval function and only then will zvint try to search for whatever value myVar will emit.

How it works

ZVINT unlike most compilers uses only Lexical, Syntax & Value processors. But the only process the user must understand is the 'context'. To make ZVINT return return a result a context value must be specified to Context and then passed to the interpreter.

Initialize by creating a context.

val globalContext = Context().apply {
    poolVariables["value1"] = "hello"
    poolVariables["value2"] = "1"
    poolVariables["value3"] = "true"
    poolVariables["value4"] = arrayListOf("a1", "a2", "a3")
}

So when ZVINT looks for variable with name "value2" it should be able to get "1". However, for now, only string and array of strings are supported for poolVariables.

One more thing is added for convenience which is called eval.

 val globalContext = Context().apply {
    eval = object: Evaluator {
        override fun eval(vararg variable: Any): Any? {
            return when {
                variable[0] == "value" -> {
                    object: InterpreterCallback {
                        override fun call(): Any? = "hello"
                    }
                }
            }
        }
    }
 }

if ZVINT cannot find value inside poolVariables then it will try to look inside eval function. The function then has to return either a string or InterpreterCallback. In some cases where you have to call a function poolVariables will not be called instead eval is called.

eval function is subject to change

After supplying a context you can simply do

val result = ZLSInterpreter(globalContext).interpret(code)

to get the desired result.