bottom-up implementation: n. Hackish opposite of the techspeak
term `top-down design'. It has been received wisdom in most
programming cultures that it is best to design from higher levels of
abstraction down to lower, specifying sequences of action in
increasing detail until you get to actual code. Hackers often find
(especially in exploratory designs that cannot be closely specified
in advance) that it works best to _build_ things in the opposite
order, by writing and testing a clean set of primitive operations
and then knitting them together. Naively applied, this leads to
hacked-together bottom-up implementations; a more sophisticated
response is `middle-out implementation', in which scratch code
within primitives at the mid-level of the system is gradually
replaced with a more polished version of the lowest level at the
same time the structure above the midlevel is being built.
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