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#! perl -l

...
# f(x)
print $g->("x");
# g(x)

sub compose2 {
    my ($f, $g) = @_;
    sub { $f->( $g->(@_) ) }
}

my $h = compose2( $f, $g );
print $h->("x");
# f(g(x))

sub foldl {
    my $f = shift;
...
sub compose {
    foldl( \&compose2, @_ )
}

print compose( $f,$f,$f,$f,$f,$f,$g )->("x");
# f(f(f(f(f(f(g(x)))))))
...

print compose( ($add1) x 4 )->(0);
# 4