On Mon, May 2, 2011 at 8:23 PM, Nicolas Buduroi <[email protected]> wrote:
> Is there a more functional way of writing it?
If you have imperative code implementing a conceptually-pure function,
the answer to this is always "yes", in at least a trivial sense: you
can write a pure-functional interpreter for the imperative code's
language that that is something like
(defn step [world-state]
(apply-instruction
(get-next-instruction world-state)
world-state))
(defn run [program & arg-list]
(let [world-state (initial-state-for program arg-list)]
(extract-output-from
(first
(drop-while
#(not (done-state? %))
(iterate step world-state))))))
Here, get-next-instruction figures out what instruction to apply next
from a world-state (e.g. it reads a program counter and then an opcode
from an address); apply-instruction applies an instruction to a
world-state to output a new world-state; initial-state-for? takes an
imperative function and an argument list and returns an initial
world-state for executing it in the virtual machine; done-state?
checks if a world-state represents an imperative function that's
finished running rather than still running; and extract-output-from
extracts the return value of that program. If all of those are pure
functions, then so is run.
But I expect most who ask "is there a more functional way of writing
it?" are hoping for something less trivial. :)
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