Resurrection of whiteknight's eval_pmc branch

Patrick R. Michaud pmichaud at
Mon Feb 18 17:11:20 UTC 2013

On Mon, Feb 18, 2013 at 08:16:41AM -0500, Andrew Whitworth wrote:
> The way the Eval PMC worked was that it returned a list of Subs, and I
> think the one at index zero was the sub marked :main. 

No.  The Eval PMC contains subs in the order in which they appear in
the source, regardless of which sub is marked ":main".  

    pmichaud at kiwi:~/p6/parrot$ cat z.pir
    .sub 'main' :main
        .local pmc fh
        .local string ypir
        # read source to be compiled from y.pir
        fh = new ['FileHandle']
        ypir = fh."readall"()
        # display y.pir
        say "y.pir source:"
        say ypir
        # compile y.pir
        .local pmc pirc, ypbc
        pirc = compreg "PIR"
        ypbc = pirc(ypir)
        # display type of object returned
        print "typeof object returned from PIR compiler: "
        $S0 = typeof ypbc
        say $S0
        # display sub at position zero
        print "sub at position zero: "
        $P0 = ypbc[0]
        say $P0
    pmichaud at kiwi:~/p6/parrot$ ./parrot z.pir
    y.pir source:
    .sub 'zero'
        say 'zero'
    .sub 'one'
        say 'one'
    .sub 'two' :main
        say 'two :main'
    .sub 'three'
        say 'three'
    typeof object returned from PIR compiler: Eval
    sub at position zero: zero
    pmichaud at kiwi:~/p6/parrot$ 

In the above example, the first element of the Eval PMC (the one
at position zero) is "zero", while .main_sub() would seem to return
"two", which is not what NQP/Rakudo would be expecting or wanting.

> The PackfileView
> PMC has a method .main_sub(), which does the same thing more
> explicitly. At least, that's how I remember it. so it's the same Sub
> being executed, we just get access to it in a different way.

No, it's not the same sub (see above).  And in the case of NQP 
and Rakudo, we generally need access to the first sub in order 
to set its outer lexical context or other properties, not because 
it's the "main" sub or the one that is to be executed.


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