If I evaluate:
(:content {:foo "bar" :biz "baf" :content ("Happy Happy Joy Joy")}) I get:
java.lang.String cannot be cast to clojure.lang.IFn If I wanted the "Happy Happy Joy Joy" string, how do I get it?
In my case, the hash-map is what I have to work with... I didn't create the string value inside a list. I understand clojure considers it a function as it's in the calling position.
If you're defining that list literally in your code, you'll need to "quote" it so that it isn't evaluated as a function:
user=> (:content {:foo "bar" :biz "baf" :content '("Happy Happy Joy Joy")}) ("Happy Happy Joy Joy") The only difference here is the ' character before the opening list parenthesis. You could also use the list function.
If you want just the first item in the :content list, you can then use first:
user=> (first (:content {:foo "bar" :biz "baf" :content '("Happy Happy Joy Joy")})) "Happy Happy Joy Joy" 
(...), but if you try to evaluate that verbatim in the REPL it will interpret the parenthesized form as a function call.What is typed that has to include quote (') literals to prevent the error message you are getting will be different from what is being returned from a function that does not have to have quotes in it. So just play with it a bit for the real (non REPL) case.
(def x '(:content {:foo "bar" :biz "baf" :content '("Happy Happy Joy Joy")})) (-> x second :content second first) ;;=> "Happy Happy Joy Joy" For the real case (-> x second :content first) might be what you want, where of course x is the function call.
If as you say it is only the hash-map (m) you are concerned with then (-> m :content first) should do the trick.
One solution to the mismatch between the REPL and reality is to just use vectors instead of lists:
(def x [:content {:foo "bar" :biz "baf" :content ["Happy Happy Joy Joy"]}]) Here (-> x second :content first) will indeed work.
The other answers did not fully clarify the effect of quote. Please see this code:
(ns tst.demo.core (:use tupelo.test) (:require [tupelo.core :as t] )) ; Note: ; (def data {:foo "bar" :biz "baf" :content ("Happy Happy Joy Joy")}) ; => exception (def data-1 '{:foo "bar" :biz "baf" :content ("Happy Happy Joy Joy")}) (def data-2 {:foo "bar" :biz "baf" :content '("Happy Happy Joy Joy")}) (def data-3 (quote {:foo "bar" :biz "baf" :content ("Happy Happy Joy Joy")})) (dotest (is= data-1 data-2 data-3) (is= "Happy Happy Joy Joy" (first (:content data-1))) (is= "Happy Happy Joy Joy" (first (:content data-2))) (is= "Happy Happy Joy Joy" (first (:content data-3)))) So, data-1 shows we can quote the entire expression at the outer level, and data-2 shows we can also quote each list expression (stuff in parens) to suppress the "function call" interpretation of a "list" type in Clojure.
data-3 shows that the single-quote char ' is just short for the special form (quote ...) in Clojure.
Once you get the data literal form right, we see that data-1 and data-2 and data-3 actually result in identical data structures after being processed by the reader.
The last 3 tests show the proper syntax for extracting the string of interest from any of the 3 data structures.
P.S. The testing stuff dotest and is= is from the Tupelo library.
