I'm trying my hand at a text adventure in clojure.
This is where I am struggling:
(ns records)
(defrecord Room [fdesc sdesc ldesc exit seen])
(defrecord Item [name location adjective fdesc ldesc sdesc flags action ])
(def bedroom (Room. "A lot of text."
nil
"some text"
'(( "west" hallway wearing-clothes? wear-clothes-f))
false))
(def hallway (Room. "description of room."
nil
"short desc of room."
'(("east" bedroom) ("west" frontdoor))
false))
(def location (ref bedroom))
(defn in?
"Check if sequence contains item."
[item lst]
(some #(= item %) lst))
(defn next-location
"return the location for a entered direction"
[direction ]
(second (first (filter #(in? direction %) (:exit #location)))))
(defn set-new-location
"set location parameter to new location."
[loc]
(dosync (ref-set location loc)))
My problem is with updating the var location.
If I enter (set-new-location hallway) it works correctly. Location is set to the new room and I can access its fields. However, what I need to do is read the next possible exit from the exit field of a room, but when I enter (set-new-direction (next-exit "west")) location says hallway, but it doesn't point to the variable "hallway".
In CL I'd use (symbol-value hallway). How can I do this in Clojure?
EDIT: I really want to use var-per-location because I have sketched out roughly 30 locations, at 20 lines each, making it too unwieldy to put in one map.
You can use #(resolve sym) as a symbol-value workalike; what it actually does is look up the Var named by the symbol sym in the current namespace (might be a Var brought in with use / require :refer) and extract its value. See ns-resolve if you want to control the namespace the Var is looked up in.
You could also not use Var-per-location, but rather store your locations in a map somewhere:
(def locations {:hallway ... :bedroom ...})
(You could also put this map in a Ref for convenience of adding new locations at runtime.)
Related
Say I have a collection of user-ids i.e. [001 002 003], and then I would have a function that does something and requires the user-id as its first argument.
(defn some-function [user-id name e-mail] (do-something user-id name e-mail))
What I'd like to do is to use this "some-function" to go through the collection of user-ids so that it would just change the user-id argument but the other arguments would remain the same i.e. so that it would return the following:
=>
[(some-function 001 name e-mail) (some-function 002 name e-mail) (some-function 003 name e-mail)]
Any help here? :) Thanks!
You can just use map:
(map #(some-function % name email) user-ids)
If "does something" is side-effecting then you should be using doseq rather than map:
(def user-ids [1 2 3])
(def email "me#my.com")
(def named "me")
(defn some-function [id name email]
(println (str id ", " name ", " email)))
(doseq [user-id user-ids]
(some-function user-id named email))
"Doing something" normally means affecting the world in some way - from printing to the screen to launching rockets into space.
However if you wanted to return a series of functions that can be executed later then map would be fine:
(def fns (map (fn [id]
(fn []
(some-function id named email)))
user-ids))
Here fns is the data structure you wrote out in your question.
To actually execute these 'thunks' you still need to doseq:
(doseq [f fns]
(f))
As a side-note, the kind of function you are talking about, that accepts different arguments at different times, is normally described as a 'higher order function', and it is best to code it that way from the start:
(defn some-function-hof [name email]
(fn [id]
(println (str id ", " name ", " email))))
(def some-fn! (some-function-hof named email))
I am trying to do the following:
1. I have multiple agents who are maps that contain expressions.
(see first three lines of code)
What I want is, on a given date inside a let scope, the above expression form the map should bind to the local date.
(rest of the lines)
What am i doing wrong, how should I approach this problem? Thanks.
--- all code below
(def dates [20171002 20171003])
(def date 20171002)
(def data (zipmap dates (repeatedly (count dates) #(ref {:entry true :exit true} )) ))
(dosync (alter (data 20171003) assoc-in [:entry] false))
(println data)
(def agent-1 {:entry-condition '((data date) :entry)})
;(eval (:entry-condition agent-1))
;(data date)
(def date-given 20171003)
(let [date date-given
enter? (eval (:entry-condition agent-1))]
(if enter? (println "hi") (println "correct")))
;; i need correct, not hi.
First things first, +1 to #amalloy comment that this eval is not you friend here (some say evil).
The root cause of the problem here is that eval looks in the current namespace and not the current lexical scope. That is further explained in this answer.
So, to rebind date, you need to use binding rather than let (at least for the date symbol). It then also needs to be dynamic. In your def of date, you can make it dynamic with:
(def ^:dynamic date 20171002)
;; or better yet:
(declare ^:dynamic date)
then when you use it,
(binding [date date-given]
(let [enter? (eval (:entry-condition agent-1))]
(if enter?
(println "NO")
(println "correct") )) )
I have this small game world state, something like the following:
(defn odds [percentage]
(< (rand-int 100) percentage))
(defn world []
{:entities []})
(defn make-bird []
{:pos [(rand-int 100) (rand-int 100)]
:age 0
:dir (vec/dir (rand (. Math PI)))})
(defn generate-entities [entities]
(if (odds 10)
(conj entities (make-bird))
entities))
(defn update-entity [entity]
(-> entity
(update :pos (partial vec/add (:dir entity)))
(update :age inc)))
(defn update-entities [entities]
(vec (map update-entity entities)))
(defn old? [{age :age}]
(> age 10))
(defn prune-entities [entities]
(vec (filter #(not (old? %)) entities)))
(defn update-world [world]
(-> world
(update :entities generate-entities)
(update :entities update-entities)
(update :entities prune-entities)))
So update-world goes through three steps. First there's a 1/10 chance of generating a new bird entity, which flies in a random direction. Then it updates all birds, updating their position and incrementing their age. Then it prunes all old birds.
I use this same technique for generating particles systems. You can do fun stuff like (iterate update-world (world)) to get a lazy list of world states which you can consume at whatever frame rate you want.
However, I now have a game world with autonomous entities which roam around and do stuff, kind of like the birds. But I want to get a textual representation of what happened when evaluating update-world. For example, update-world would ideally return a tuple of the new world state and a vector of strings - ["A bird was born at [12, 8].", "A bird died of old age at [1, 2]."].
But then I really can't use (iterate update-world (world)) anymore. I can't really see how to do this.
Is this something you'd use with-out-string for?
If you want to enhance only your top-level function (update-world) in your case you can just create a wrapper function that you can use in iterate. A simple example:
(defn increment [n]
(inc n))
(defn logging-increment [[_ n]]
(let [new-n (increment n)]
[(format "Old: %s New: %s" n new-n) new-n]))
(take 3 (iterate logging-increment [nil 0]))
;; => ([nil 0] ["Old: 0 New: 1" 1] ["Old: 1 New: 2" 2])
In case you want to do it while collecting data at multiple level and you don't want to modify the signatures of your existing functions (e.g. you want to use it only for debugging), then using dynamic scope seems like a reasonable option.
Alternatively you can consider using some tracing tools, like clojure/tools.trace. You could turn on and off logging of your function calls by simply changing defn to deftrace or using trace-ns or trace-vars.
There are two potential issues with using with-out-str
It returns a string, not a vector. If you need to use a vector, you'll need to use something else.
Only the string is returned. If you are using with-out-str to wrap a side-effect (e.g., swap!), this might be fine.
For debugging purposes, I usually just use println. You can use with-out if you want control over where the output goes. You could even implement a custom stream that collects the output into a vector of strings if you wanted. You could get similar results with a dynamically bound vector that you accumulate (via set!) the output string (or wrap the vector in an atom and use swap!).
If the accumulated vector is part of the computation per se, and you want to remain pure, you might consider using a monad.
What about using clojure.data/diff to generate the string representation of changes? You could do something like this:
(defn update-world [[world mutations]]
(let [new-world (-> world
(update :entities generate-entities)
(update :entities update-entities)
(update :entities prune-entities))]
[new-world (mutations (clojure.data/diff world new-world))]))
Then you could do something like (iterate update-world [(world) []]) to get the ball rolling.
I am working on a simple web-app using clojurescript and reagent. I would like to create a simple "tab" component, which will contain (for starters) a text-input component.
The app has 2 tabs and the user has the option to choose a tab and I want to "preserve" the values in each of these two tabs.
Here's the code:
(defn atom-input [value]
[:input {:type "text"
:value #value
:on-change #(reset! value (-> % .-target .-value))}])
(defn simple-tab [index]
(let [pg-index (atom 1)
a (atom 0)]
(fn []
[:div
[:h4 (str "index: " #index)]
[atom-input a]])))
(defn main-page []
(let [index (atom 0)]
[:div.container
[:div.row
[:button {:on-click (fn [] (reset! index 0))} "select tab 1"]
[:button {:on-click (fn [] (reset! index 1))} "select tab 2"]]
[:div.row
[simple-tab index]]]))
(defn ^:export run []
(reagent/render-component
(fn [] [main-page])
(.-body js/document)))
The problem is that when I switch the tab, the components share the values of the input field - what am I please doing wrong here?
Thank you so much for your help!
The problem is you're passing a (atom 0) to the atom-input control: [atom-input a].
This caused the same atom value to be shared between your tabs.
If you don't want to share the value, you'll need change a to a map: a (atom {}) and pass the map and the index to atom-input, e.g.:
(defn atom-input [value index]
[:input {:type "text"
:value (or (get #value index) "")
:on-change #(swap! value assoc index (-> % .-target .-value))}])
(defn simple-tab [index]
(let [pg-index (atom 1)
a (atom {})]
(fn []
[:div
[:h4 (str "index: " #index)]
[atom-input a #index]])))
A better approach, IMHO, is to use cursor so you don't need to pass the index & the whole map to atom-input, e.g.:
(defn atom-input [value]
[:input {:type "text"
:value (or #value "")
:on-change #(reset! value (-> % .-target .-value))}])
(defn simple-tab [index]
(let [pg-index (atom 1)
a (atom {})]
(fn []
[:div
[:h4 (str "index: " #index)]
[atom-input (reagent/cursor [#index] a)]])))
I think there are a couple of problems here because you are mixing up application data (state) and display logic data (i.e. DOM). If you keep the two things distinct i.e. maintain your application state in one atom and data relating to component display in another, then things may be a bit cleaner.
Your simple-tab component does not need to know anything about the tab state. It just needs to know about the app state i.e. the value entered/stored via atom-input. Therefore, rather than passing it index, pass it the atom you want it to use. this would require some higher level logic to determine the call. for example, if you had a number of tabs, you might have something like
(condp = #index
0 [simple-tab tab0-atom]
1 [simple-tab tab1-atom]
...
n [simple-tab tabn-atom])
or you could modify simple-tab so that the value passed in i.e. index value is used as a key into the app-state - a cursor would be easiest I think i.e.
(def app-state (r/atom {:tabs {0 nil 1 nil}}})
(defn simple-tab [index]
(let [val-cur (r/cursor app-state [:tabs index])]
[atom-input val-cur]))
You are using a form-2 component, that is, a component that returns a function.
More details here : https://github.com/Day8/re-frame/wiki/Creating-Reagent-Components#form-2--a-function-returning-a-function
When doing so, only the returned function is called so your atom-inputs are sharing the same atom.
Also, you should use the same argument in the inner function
(defn simple-tab [index]
(let [pg-index (atom 1)
a (atom {})]
(fn [index]
[:div
[:h4 (str "index: " #index)]
[atom-input a #index]])))
In your case, you are passing an atom so this is not important but you could have error in the future if you forgot this.
Concerning the broader architecture, I would advise you to use a single global atom. Try to have as much as possible state in this atom and avoid component local state so this is easier to reason about.
You could also name your tabs like :product :users and use a multimethod to render the correct tab based on the selected one. This is easier to read and easier to add new tabs in the future.
I have a function that begins like this:
(defn data-one [suser]
(def suser-first-name
(select db/firstNames
(fields :firstname)
(where {:username suser})))
(def suser-middle-name
(select db/middleNames
(fields :middlename)
(where {:username suser})))
(def suser-last-name
(select db/middleNames
(fields :lastname)
(where {:username suser})))
;; And it just continues on and on...
)
Of course, I don't like this at all. I have this pattern repeating in many areas in my code-base and I'd like to generalize this.
So, I came up with the following to start:
(def data-input {:one '[suser-first-name db/firstNames :firstname]
'[suser-middle-name db/middleNames :middlename]
'[suser-last-name db/lastNames :lastname]})
(defpartial data-build [data-item suser]
;; data-item takes the arg :one in this case
`(def (data-input data-item)
(select (data-input data-item)
(fields (data-input data-item))
(where {:username suser}))))
There's really a few questions here:
-- How can I deconstruct the data-input so that it creates x functions when x is unknown, ie. that the values of :one is unknown, and that the quantities of keys in data-input is unknown.
-- I'm thinking that this is a time to create a macro, but I've never built one before, so I am hesitant on the idea.
And to give a little context, the functions must return values to be deconstructed, but I think once I get this piece solved, generalizing all of this will be doable:
(defpage "/page-one" []
(let [suser (sesh/get :username)]
(data-one suser)
[:p "Firat Name: "
[:i (let [[{fname :firstname}] suser-first-name]
(format "%s" fname))]
[:p "Middle Name: "
[:i (let [[{mname :emptype}] suser-middle-name]
(format "%s" mname))]
[:p "Last Name: "
[:i (let [[{lname :months}] suser-last-name]
(format "%s" lname))]]))
Some suggestions:
def inside a function is really nasty - you are altering the global environment, and it can cause all kinds of issues with concurrency. I would suggest storing the results in a map instead.
You don't need a macro here - all of the data fetches can be done relatively easily within a function
I would therefore suggest something like:
(def data-input [[:suser-first-name db/firstNames :firstname]
[:suser-middle-name db/middleNames :middlename]
[:suser-last-name db/lastNames :lastname]])
(def data-build [data-input suser]
(loop [output {}
items (seq data-input)]
(if items
(recur
(let [[kw db fieldname] (first items)]
(assoc output kw (select db (fields fieldname) (where {:username suser}))))
(next items))
output)))
Not tested as I don't have your database setup - but hopefully that gives you an idea of how to do this without either macros or mutable globals!
Nice question. First of all here's the macro that you asked for:
(defmacro defquery [fname table fields ]
(let [arg-name (symbol 'user-name)
fname (symbol fname)]
`(defn ~fname [~arg-name]
(print ~arg-name (str ~# fields)))))
You can call it like that:
(defquery suser-first-name db/firstNames [:firstname])
or if you prefer to keep all your configurations in a map, then it will accept string as the first argument instead of a symbol:
(defquery "suser-first-name" db/firstNames [:firstname])
Now, if you don't mind me recommending another solution, I would probably chose to use a single function closed around configuration. Something like that:
(defn make-reader [query-configurations]
(fn [query-type user-name]
(let [{table :table field-names :fields}
(get query-configurations query-type)]
(select table
(apply fields field-names)
(where {:username suser})))))
(def data-input {:firstname {:table db/firstNames :fields :firstname}
:middlename {:table db/middleNames :fields :middlename}
:lastname {:table db/lastNames :fields :lastname}})
(def query-function (make-reader data-input))
;; Example of executing a query
(query-function :firstname "tom")
By the way there's another way to use Korma:
;; This creates a template select from the table
(def table-select (select* db/firstNames))
;; This creates new select query for a specific field
(def first-name-select (fields table-select :firstname))
;; Creating yet another query that filters results by :username
(defn mkselect-for-user [suser query]
(where query {:username suser}))
;; Running the query for username "tom"
;; I fully specified exec function name only to show where it comes from.
(korma.core/exec (mkselect-for-user "tom" first-name-select))
For more information I highly recommend looking at Korma sources.