Re: Lua parser question re function calls in local statement

[Dibyendu Majumdar <mobile@...>]

On 17 January 2015 at 16:36, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> local i,j,k = f(), g()
>
> Initially the OP_CALL instruction has operand C set to 2 for both the
> calls, but later on the call to g() is patched so that C is set to 3
> for the call to g(). I was trying to generate special op codes to
> coerce types after each function call - but the problem is at the time
> of call to the function the parser does not know how many values to
> assign from the function call. As code for f() has already been
> generated by the time the call to g() is patched - I cannot go back
> and insert extra instructions, especially as some expressions go back
> and update specific instructions so all those anchors would be
> invalidated by any insertion of new instructions.
>
> The inefficient way seems to be to apply type coercion to i,j, and k
> after call to f() and then again to j,k after call to g() ;-(
>
> So back to the drawing board.

Looks like there is an easy solution to this:
Initially generate instructions for 1 return value for each function.
Then after the call to g() is patched, generate extra instructions for
the remaining values - as these are guaranteed to be at the end.

So for example:

local i:int, j:double = f()

Produces:

        1       [1]     GETTABUP        0 0 -1  ; _ENV "f"
        2       [1]     CALL            0 1 3
        3       [1]     TOINT   0 0 0
        4       [1]     TOFLT   1 0 0
        5       [1]     RETURN          0 1

And:

local i:int, j:double, k:int = f(), g()

Produces:

        1       [1]     GETTABUP        0 0 -1  ; _ENV "f"
        2       [1]     CALL            0 1 2
        3       [1]     TOINT   0 0 0
        4       [1]     GETTABUP        1 0 -2  ; _ENV "g"
        5       [1]     CALL            1 1 3
        6       [1]     TOFLT   1 0 0
        7       [1]     TOINT   2 0 0
        8       [1]     RETURN          0 1


Here TOFLT and TOINT are new instructions that perform tointeger and
tonumber on register value at A.