Re: Easier imperative-style programming
Here's an example of using a state monad for updating a position. The state
goes into a simple map and there's a function to add coordinates.
(def init {:position [100 100] :st :st0 :keys-held #{:left}})
(defn v+ [v1 v2] (vec (map + v1 v2)))
The state monad can compute a value and maintain some arbitrary state. In
this case, the statements produce side-effects but nothing is actually
computed, which is fine. You'd want to model each statement to encapsulate
some action and return a State instance. For simplicity, the function move
mixes the conditional statement with the then-branch, but that can be
easily separated later:
;; shameless plug
(use 'blancas.morph.core
'blancas.morph.monads)
(defn move [key v]
(monad [held (gets :keys-held)]
(if (held key)
(modify-state #(update-in % [:position] v+ v))
(state :empty-stmt
This function takes the key that was pressed. If it's one held in storage,
the state will be modified pretty much the way it was before; otherwise the
statement evaluates into a state instance whose value is the empty
statement.
Each of the following elements models a conditional statement: if x do this:
(def stmts [(move :left [-10 0])
(move :right [ 10 0])
(move :up[ 0 -10])
(move :down [ 0 10])])
This "runs" the sequence of monads and returns the value of the resulting
state (not the value since it's not computing anything:
(exec-state (seqm stmts) init)
;; {:position [90 100], :st :st0, :keys-held #{:left}}
Here we do the same but then change the key and re-evaluate the statements.
The combinators seqm and >> are similar; seqm takes a collection.
(exec-state (>> (seqm stmts)
(modify-state assoc :keys-held #{:down})
(seqm stmts))
init)
;; {:position [90 110], :st :st0, :keys-held #{:down}}
This shows a computation; say you want to compute: [50 50] + [12 -5]
For this you'd write a new version of v+ that takes "monadic" args (boxed
in a State). As above, the (monad) macro binds the results of monads to the
variables, as in a let. Then wraps the result in a state:
(defn v+ [v1 v2]
(monad [x v1 y v2]
(state (vec (map + x y)
(This function could take simple vectors, but in a real use case you'd be
taking expressions, not just values.)
Now you can get the result like so:
(eval-state (v+ (state [50 50]) (state [12 -5])) init)
;; [62 45]
If you want both the computed value and the finate state you can get them
both in a Pair:
(run-state (v+ (state [50 50]) (state [12 -5])) init)
;; Pair([62 45],{:position [100 100], :st :st0, :keys-held #{:left}})
On Monday, February 11, 2013 12:10:24 PM UTC-8, JvJ 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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Re: Easier imperative-style programming
You want to think more abstractly. What are the common elements in your
code?
For instance, a naive first pass:
(defn move [subject delta]
(update-in subject [:position] v+ delta))
(defn key-held [key]
(@*keys-held* :left))
(defmacro on [subject event action]
`(if ~event (-> ~subject ~action))
Then you could write:
(-> g
(on (key-held :left) (move [-10 0]))
(on (key-held :right) (move [10 0]))
(on (key-held :up) (move [0 -10]))
(on (key-held :down) (move [0 10]))
But if you're designing a game, you usually want to separate the event loop
from the event handling. That's a big topic though, and I can't really go
into much detail in a single post.
- James
On 11 February 2013 20:10, JvJ 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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Re: Easier imperative-style programming
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 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 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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Re: Easier imperative-style programming
I think cond-> would work well
https://github.com/clojure/clojure/blob/master/changes.md#24-new-threading-macros
On Mon, Feb 11, 2013 at 3:10 PM, JvJ 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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Re: Easier imperative-style programming
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 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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Easier imperative-style programming
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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