github.com/coyove/nj@v0.0.0-20221110084952-c7f8db1065c3/README.md

NJ is a simple script engine written in golang with Lua-like syntax.

(If you are looking for a Lua 5.2 compatible engine, refer to tag `v0.2`)

## Differ from Lua

- There is no `table`, instead there are `array` and `object` respectively:
	- `a=[1, 2, 3]`.
	- `a={a=1, b=2}`.
	- Empty array and empty object are `true` when used as booleans.
- There are `typed` array and `untyped` array:
	- Untyped arrays are generic arrays created by `[...]`, it is the builtin array type.
	- Typed arrays are special arrays created by Go, say `[]byte`:
		- `a = bytes(16)` creates a 16-byte long `[]byte`.
		- `a.append(1)` appends 1 to it.
		- `a.append(true)` will panic.
		- `a.untype().append(true)` will `untype` the array into a (new) generic array.
- Functions are callable objects:
	- `function foo() end; assert(type(foo), "object")`
	- `function foo() end; assert(foo is callable)`
- Closures are created by capturing all symbols seen in the current scope and binding them to the returned function:
	- `function foo(a, b) return function(c) return self.a + self.b + c end end`
    - `assert(foo(1, 2)(3), 6)`
- Syntax of calling functions strictly requires no spaces between the callee and '(':
	- `print(1)` is the only right way of calling a function.
	- `print (1)` literally means two things: 1) get value of `print` and discard it, 2) evaluate `(1)`.
    - Also note that all required arguments must be provided to call a function properly:
        - `function foo(a, b) end; foo(1)` is invalid.
- Spacing rule also applies to unary operator `-`:
	- `a = 1-a <=> a = 1 - a` means assign the result of `1-a` to `a`.
	- `a = 1 -a` means assign `1` to `a` and negate `a`.
	- `a = 1 -a+1` means assign `1` to `a` and eval `-a+1`.
	- `a = -a` means negate `a` and assign the result to `a`.
	- `a = - a` is invalid.
- There are two ways to write `if`:
	- `if cond then true else false end` as a statement.
	- `local a = if(cond, true, false)` as an expression.
	- `if(cond) then ... end` is invalid, spaces after `if` statement is mandatory.
	- `if (cond, true, false)` is invalid, spaces after `if` expression is not allowed.
- To write variadic functions:
	- `function foo(a, b...) end; args = [1, 2, 3]; foo(args...)`.
    - Parameters after `...` are optional:
	    - `function foo(a ... b, c) end; foo(1); foo(1, 2); foo(1, 2, 3)`
- Returning multiple arguments will be translated into returning an array, e.g.:
	- `function foo() return 1, 2 end <=> function foo() return [1, 2] end`
	- `local a, b, c = d <=> local a, b, c = d[0], d[1], d[2]`
- Everything starts at ZERO. For-loops start inclusively and end exclusively, e.g.:
	- `a=[1, 2]; assert(a[0] == 1)`.
	- `for i=0,n do ... end` ranges `[0, n-1]`.
	- `for i=n-1,-1,-1 do ... end` ranges `[n-1, 0]`.
- For method function, it can access `this` which points to the receiver:
	- `a={}; function a.foo(x) this.x = x end; a.foo(1); assert(a.x, 1)`
- For any function, use `self` to get itself in the body:
    - `function foo(x) self.x = x end; foo(1); assert(foo.x, 1)`
- You can define up to 32000 variables (varies depending on the number of temporal variables generated by interpreter) in a function.
- Numbers are `int64 + float64` internally, interpreter may promote it to `float64` when needed and downgrade it to `int64` when possible.
- You can `return` anywhere inside functions, `continue` inside for-loops, `goto` any label within the same function.

## Run

```golang
program, err := nj.LoadString("return 1")
v, err := program.Run() // v == 1
```

### Global Values

```golang
bas.AddGlobal("G", bas.ValueOf(func() int { return 1 }))

program, _ := nj.LoadString("return G() + 1")
v, err := program.Run() // v == 2

program, _ = nj.LoadString("return G() + 2")
v, err = program.Run() // v == 3

program, _ = nj.LoadString("return G + 2", &CompileOptions{
	Globals: bas.NewObject(0).SetProp("G", 10).ToMap(), // override the global 'G'
})
v, err = program.Run() // v == 12
```

## Benchmarks

Refer to [here](https://github.com/coyove/nj/blob/master/tests/bench/perf.md).