get value from dynamic key in clojure map

Question

I have a clojure map ``` + 69 (def names {:production "prayag" + 70 :staging "upd"}) ``` I need to get a value from a key variable `environment` that would be dynamic. Something like below throws Exception, ``` + 72 (defn get-name [environment] + 73 (let [ + 74 name (:(environment) names)] + 75 println name + 76 )) ``` Stacktrace ``` Caused by: java.lang.RuntimeException: Invalid token: : at clojure.lang.Util.runtimeException(Util.java:219) at clojure.lang.LispReader.interpretToken(LispReader.java:326) at clojure.lang.LispReader.read(LispReader.java:211) at clojure.lang.LispReader.readDelimitedList(LispReader.java:1157) at clojure.lang.LispReader$ListReader.invoke(LispReader.java:982) at clojure.lang.LispReader.readDelimitedList(LispReader.java:1148) at clojure.lang.LispReader$VectorReader.invoke(LispReader.java:1083) at clojure.lang.LispReader.readDelimitedList(LispReader.java:1148) at clojure.lang.LispReader$ListReader.invoke(LispReader.java:982) at clojure.lang.LispReader.readDelim…

Accepted Answer

`(:(environment) names)` is not a valid form. Unless `environment` is a function of no arguments, you will get an error from wrapping it in parens. usage of `:` to create keywords is done at read time, before `(environment)` is evaluated, so you do not see the previous error, and the reader attempts to resolve `:` on its own, which is not a valid input to the reader.

`(keyword(":" env) names)` attempts to call the string ":" as if it were a function. It is not one. Also the spacing leads me to beleive that you expect `keyword(arg)` to work as it would in an Algol family language. It will not. The proper usage is `(keyword arg)`.

here is what works, with a few equivalent syntaxes avaliable for convenience (they all do the same thing):

```
user> (def names {:production "prayag" :staging    "upd"})
#'user/names
user> (def environment "staging")
#'user/environment
user> (names (keyword environment))
"upd"
user> ((keyword environment) names)
"upd"
user> (get names (keyword environment))
"upd"
```

get value from dynamic key in clojure map

Solution

Problem