Streaming functions and recursion, part 4

Following up on the previous installment, here is the example that uses the bindings with tray:

###
# A streaming function that computes a Fibonacci number.

# Input:
#   $lbFibCompute: request to compute the number.
# Output (by FnReturn labels):
#   "result": the computed value.
# The opcode is preserved through the computation.

my @stackFib; # stack of the function states
my $stateFib; # The current state

my $frFib = Triceps::FnReturn->new(
    name => "Fib",
    unit => $uFib,
    labels => [
        result => $rtFibRes,
    ],
    onPush => sub { push @stackFib, $stateFib; $stateFib = { }; },
    onPop => sub { $stateFib = pop @stackFib; },
);

my $lbFibResult = $frFib->getLabel("result");

# Declare the label & binding variables in advance, to define them sequentially.
my ($lbFibCompute, $fbFibPrev1, $fbFibPrev2);
$lbFibCompute = $uFib->makeLabel($rtFibArg, "FibCompute", undef, sub {
    my $row = $_[1]->getRow();
    my $op = $_[1]->getOpcode();
    my $idx = $row->get("idx");

    if ($idx <= 1) {
        $uFib->makeHashCall($frFib->getLabel("result"), $op,
            idx => $idx,
            fib => $idx < 1 ? 0 : 1,
        );
    } else {
        $stateFib->{op} = $op;
        $stateFib->{idx} = $idx;

        {
            my $ab = Triceps::AutoFnBind->new(
                $frFib => $fbFibPrev1
            );
            $uFib->makeHashCall($lbFibCompute, $op,
                idx => $idx - 1,
            );
        }
        $fbFibPrev1->callTray();
    }
}) or confess "$!";
$fbFibPrev1 = Triceps::FnBinding->new(
    unit => $uFib,
    name => "FibPrev1",
    on => $frFib,
    withTray => 1,
    labels => [
        result => sub {
            $stateFib->{prev1} = $_[1]->getRow()->get("fib");

            # must prepare before pushing new state and with it new $stateFib
            my $rop = $lbFibCompute->makeRowopHash($stateFib->{op},
                idx => $stateFib->{idx} - 2,
            );

            {
                my $ab = Triceps::AutoFnBind->new(
                    $frFib => $fbFibPrev2
                );
                $uFib->call($rop);
            }
            $fbFibPrev2->callTray();
        },
    ],
);
$fbFibPrev2 = Triceps::FnBinding->new(
    unit => $uFib,
    on => $frFib,
    name => "FibPrev2",
    withTray => 1,
    labels => [
        result => sub {
            $stateFib->{prev2} = $_[1]->getRow()->get("fib");
            $uFib->makeHashCall($frFib->getLabel("result"), $stateFib->{op},
                idx => $stateFib->{idx},
                fib => $stateFib->{prev1} + $stateFib->{prev2},
            );
        },
    ],
);

# End of streaming function
###

The stack depth is now greatly reduced because the unit stack pops the frames before pushing more of them. For the 2nd Fibonacci number the trace is:

unit 'uFib' before label 'FibCompute' op OP_DELETE {
unit 'uFib' before label 'FibCompute' op OP_DELETE {
unit 'uFib' before label 'Fib.result' op OP_DELETE {
unit 'uFib' after label 'Fib.result' op OP_DELETE }
unit 'uFib' after label 'FibCompute' op OP_DELETE }
unit 'uFib' before label 'FibPrev1.result' op OP_DELETE {
unit 'uFib' before label 'FibCompute' op OP_DELETE {
unit 'uFib' before label 'Fib.result' op OP_DELETE {
unit 'uFib' after label 'Fib.result' op OP_DELETE }
unit 'uFib' after label 'FibCompute' op OP_DELETE }
unit 'uFib' before label 'FibPrev2.result' op OP_DELETE {
unit 'uFib' before label 'Fib.result' op OP_DELETE {
unit 'uFib' before label 'FibCall.result' (chain 'Fib.result') op OP_DELETE {
unit 'uFib' after label 'FibCall.result' (chain 'Fib.result') op OP_DELETE }
unit 'uFib' after label 'Fib.result' op OP_DELETE }
unit 'uFib' after label 'FibPrev2.result' op OP_DELETE }
unit 'uFib' after label 'FibPrev1.result' op OP_DELETE }
unit 'uFib' after label 'FibCompute' op OP_DELETE }

For the 6th number the maximal required stack depth now gets reduced to only 9 instead of 51.