Why does lua not allow local lambda functions recursively calling themself?-CodePudding

I am trying to implement a sort of decorator pattern in Lua, and along the way I have run into an issue regarding lambda functions calling themselves.

The following code runs fine:

local function foo()
    print("bar")
    foo()
end

foo()

However the following is not allowed:

local foo = function ()
    print("bar")
    foo()
end

foo()

The interpreter throws the following error:

Exception has occurred: main.lua:27: attempt to call a nil value (global 'foo')
stack traceback:
    main.lua:27: in local 'foo'
    main.lua:30: in main chunk
    [C]: in ?

The lua documentation states that "the usual way to write a function in Lua, like function foo (x) return 2*x end is just an instance of what we call syntactic sugar; in other words, it is just a pretty way to write foo = function (x) return 2*x end", so it seems to me these should be equivalent.

What am I missing?

CodePudding user response：

in other words, it is just a pretty way to write foo = function (x) return 2*x end

Yes, that's how function works. local function works slightly differently.

The problem is that the compiler doesn't know that the foo named in the function is a local variable, because the full declaration of the local variable foo has not yet been completed. And that only happens at the end of the entire local function statement; until then, foo would refer to a global variable.

To prevent this, local function X <stuff> is syntactic sugar for two statements: local X; X = function <stuff>. You can do the same thing if you like, but the declaration of the local variable has to be a statement separate from the function expression itself.