PP(pp_grepwhile)
    ...
	if (gimme == G_SCALAR) { // Scalar context
	    dTARGET;
	    XPUSHi(items);       // Choose the scalar that gets returned.
	}
	else if (gimme == G_ARRAY)
	    SP += items;
	RETURN;
    }
...

##</code><code>##

c:\test>perl -MO=Concise -wle"print scalar( 1, 2, 3 );"
Useless use of a constant in void context at -e line 1.
8  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
7     <@> print vK ->8
3        <0> pushmark s ->4
-        <1> scalar sK/1 ->7
6           <@> list sK ->7             <<< And yet, there it is.
4              <0> pushmark v ->5
-              <0> ex-const v ->-
-              <0> ex-const v ->5
5              <$> const[IV 3] s ->6
-e syntax OK

##</code><code>##

c:\test>perl -wle"print for ( 'a','b','c' )"
a
b
c

##</code><code>##

c:\test>perl -wle"print for scalar(( 'a','b','c' ))"
Useless use of a constant in void context at -e line 1.
Useless use of a constant in void context at -e line 1.
c

##</code><code>##

c:\test>perl -wle"print for scalar 'a','b','c'"
a
b
c

c:\test>perl -wle"@a = (1,2,3); print for @a"
1
2
3

c:\test>perl -wle"@a = 1,2,3; print for @a"
Useless use of a constant in void context at -e line 1.
Useless use of a constant in void context at -e line 1.
1

##</code><code>##

PP(pp_aslice)
{
    dSP; dMARK; dORIGMARK;
    register AV* const av = (AV*)POPs;
    register const I32 lval = (PL_op->op_flags & OPf_MOD || LVRET);

    if (SvTYPE(av) == SVt_PVAV) {
        const I32 arybase = PL_curcop->cop_arybase;
        if (lval && PL_op->op_private & OPpLVAL_INTRO) {
            register SV **svp;
            I32 max = -1;
            for (svp = MARK + 1; svp <= SP; svp++) {
                const I32 elem = SvIVx(*svp);
                if (elem > max)
                    max = elem;
            }
            if (max > AvMAX(av))
                av_extend(av, max);
        }
        while (++MARK <= SP) {
            register SV **svp;
            I32 elem = SvIVx(*MARK);

            if (elem > 0)
                elem -= arybase;
            svp = av_fetch(av, elem, lval);
            if (lval) {
                if (!svp || *svp == &PL_sv_undef)
                    DIE(aTHX_ PL_no_aelem, elem);
                if (PL_op->op_private & OPpLVAL_INTRO)
                    save_aelem(av, elem, svp);
            }
            *MARK = svp ? *svp : &PL_sv_undef;
        }
    }
    if (GIMME != G_ARRAY) {
	MARK = ORIGMARK;
	*++MARK = SP > ORIGMARK ? *SP : &PL_sv_undef;
	SP = MARK;
    }
    RETURN;
}