static SV * fp = (SV*) NULL;

void call_funky() {
    dSP;

    if(fp == (SV*) NULL)
        return;

    PUSHMARK(SP);
    perl_call_sv(fp, G_DISCARD);
}

MODULE = sometin  PACKAGE = somethin

void
funky(f)
    SV *    f
    CODE:
    if (fp == (SV*)NULL)
        fp = newSVsv(f);
    else
        SvSetSV(fp, f);