coyove / nj

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, where any values can be stored inside.
  • Typed arrays are special arrays from 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; print(type(foo)) prints object.
  • function foo() end; print(foo is callable) prints true.
• Functions should be declared in the topmost scope:
  • do function foo() ... end end is invalid.
  • if true then function foo() function bar() ... end end is invalid.
  • function foo() function bar() ... end end is invalid.
• Use lambda to declare anonymous functions:
  • local foo = lambda(x) ... end.
  • Last return can be omitted: lambda (x) x=x+1; x end <=> lambda (x) x=x+1; return x end.
• Syntax of calling functions strictly requires no spaces between 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).
• Same rule 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 2 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...).
• Simple keyword arguments syntax sugar:
  • foo(a, b=2, c=3) will be converted to foo(a, {b=2, c=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].
• Every function has a this initially pointing to itself, if the function was loaded from an object, this will point to it instead:
  • function foo(x) this.x = x end; foo(1); assert(foo.x, 1)
  • a={foo=lambda(x) this.x = x end}; a.foo(1); assert(a.x, 1)
• Use debug.self() to always get the caller itself:
  • a={foo=lambda(x) debug.self().x = x end}; a.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.Globals.SetProp("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), // override the global 'G'
})
v, err = program.Run() // v == 12

Benchmarks

Refer to here.