Hello,
Below code can be compiled but says an error "attempt to call a nil value"
```
print"hello"
(function() print"world" end)()
```
luac creates this instructions:
```
main <foo.lua:0,0> (7 instructions at 0x6a5a50)
0+ params, 2 slots, 1 upvalue, 0 locals, 2 constants, 1 function
1 [1] GETTABUP 0 0 -1 ; _ENV "print"
2 [1] LOADK 1 -2 ; "hello"
3 [1] CALL 0 2 2
4 [3] CLOSURE 1 0 ; 0x6a5d30
5 [1] CALL 0 2 2
6 [1] CALL 0 1 1
7 [3] RETURN 0 1
constants (2) for 0x6a5a50:
1 "print"
2 "hello"
locals (0) for 0x6a5a50:
upvalues (1) for 0x6a5a50:
0 _ENV 1 0
function <foo.lua:3,3> (4 instructions at 0x6a5d30)
0 params, 2 slots, 1 upvalue, 0 locals, 2 constants, 0 functions
1 [3] GETTABUP 0 0 -1 ; _ENV "print"
2 [3] LOADK 1 -2 ; "world"
3 [3] CALL 0 2 1
4 [3] RETURN 0 1
constants (2) for 0x6a5d30:
1 "print"
2 "world"
locals (0) for 0x6a5d30:
upvalues (1) for 0x6a5d30:
0 _ENV 0 0
```
Look at the 4th and 5th instructions of main chunk.
At 4th instruction, it registers the annonymous function to register 1, and 5th instruction calls a function from register 0, which is empty.
That is why the code says "attempt to call a nil value".
Generally speaking, the code makes a invalid instruction like this:
```
funcall()
(exp)
```
This code can't be compiled with lua5.1, but CAN be compiled with 5.2, 5.3
It is not a problem that `exp` is function definition or variables (, even if the type is not function), but it can write number, string, and so on.
I think it should not be compiled.
And invalid instruction insertion IS a bug.
--
Kawahara Satoru
College of Information Science
University of Tsukuba
