Some swear by monads, others (like myself) tend to swear at them. I would
suggest breaking the code apart a bit more. From the looks of it, you're
writing something like a game. The first 4 clauses could be redone as
something like this:
(def dirs
{:left [-10 0]
:up [0 -10]
:right [0 10]
:down [10 0]})
(def key-maps
{:t-key :left})
(reduce
(fn [acc key]
(if (pressed? key)
(update-in acc [:position] v+ (-> key key-maps dirs))
acc))
state
keys)
Using the new reducers lib, you should be able get tolerable performance
from code like this. If you want other states (pressed, held, etc.) think
about using a multi method:
(defmulti key-dispatch (fn [state key]
[(to-char key) (pressed? key) (held?
key) (released? key)]))
(defmethod key-dispatch [\t true false false]
[state key]
(do-stuff))
Timothy
On Mon, Feb 11, 2013 at 1:12 PM, Ben Wolfson <wolf...@gmail.com> wrote:
> yes, you could do this with a state monad, though how the results will
> end up looking will depend on the particular monad implementation you
> go for.
>
> On Mon, Feb 11, 2013 at 12:10 PM, JvJ <kfjwhee...@gmail.com> wrote:
> > I'm writing a simple game engine in Clojure, and each game object
> supplies
> > its own unique update function, which takes the original object (a map of
> > properties) and returns an updated version. However, writing the
> updates is
> > somewhat cumbersome because each line of code has to return either the
> > original or updated object. I'd like to see if I can clean up this code,
> > possibly by using monads (which I don't understand very well). Does
> anyone
> > have any advice? Thanks (Code examples below)
> >
> > The pseudocode for what i want to do looks something like this:
> >
> > if left key is held
> > g.position += [-10 0]
> > if right key is held
> > g.position += [10 0]
> > if up key is held
> > g.position += [0 -10]
> > if down key is held
> > g.position += [0 10]
> > if q is pressed
> > fire event {:type :dialogue, :text "Hello"}
> > if space is pressed
> > g.switchstate(:s2)
> >
> >
> > But the code I ended up writing is this mess:
> >
> >
> > (fn [g]
> > (-> g
> > (#(if (@*keys-held* :left)
> > (update-in % [:position] v+ [-10 0])
> > %))
> > (#(if (@*keys-held* :right)
> > (update-in % [:position] v+ [10 0]) %))
> > (#(if (@*keys-held* :up)
> > (update-in % [:position] v+ [0 -10]) %))
> > (#(if (@*keys-held* :down)
> > (update-in % [:position] v+ [0 10]) %))
> > (#(if (@*keys-pressed* \q)
> > (do (fire-event {:type :dialogue
> > :text "Hello!"})
> > %)
> > %))
> > (#(if (@*keys-pressed* :space)
> > (do (comment (println "spaced!"))
> > (switch-state % :s2)) %))))
> >
> > --
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>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks,
> which may be sweet, aromatic, fermented or spirit-based. ... Family
> and social life also offer numerous other occasions to consume drinks
> for pleasure." [Larousse, "Drink" entry]
>
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