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

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

Global Values

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.