talk-transcripts

acterEncoding, startAsync, startAsync... getHeader, getHeaderNames, getHeaders, getIntHeader... "How many maps?" Vs. In Clojure, Just Use Maps {:remote-addr "127.0.0.1", :scheme :http, :query-params {"somekey" "somevalue"}, :form-params {}, :request-method :get, :query-string "somekey=somevalue", :content-type nil, :uri "/foobaz", :server-name "localhost", :params {"somekey" "somevalue"}, :headers {"accept-encoding" "gzip, deflate", "connection" "close", "user-agent" "Apache-HttpClient/4.1.2 (java 1.5)", "content-length" "0", "host" "localhost:8383"}, :content-length 0, :server-port 8383, :character-encoding nil} "In Clojure, we just use maps. This stuff came over a wire in HTTP, as text. How did we turn it into this [the Java]?"

name, package, and an empty value, function, and plist. When you (defparameter a 8) and inspect 'a again, you'll see it has a value attribute of 8. You can then (defun a ()) and inspect again, and see both the value and function attributes are set. Of course CL is a Lisp-2. Part of Clojure symbols being just names, means they aren't owned by any namespace. If you have three namespaces with functions that return 'x, they will all be value-equal to each other. Clojure symbols can be namespace-qualified, like 'some-ns/x, but that just restricts the lookup, the namespace doesn't own such a symbol. You can even make such a symbol without having defined the namespace some-ns first. In CL by contrast, if you create three functions in three different packages returning 'x, they will not be value-equal. And if you try to reference a symbol in 'some-package:x when the package doesn't exist, you'll get an error. Clojure symbols are not storage-equal though: (identical? 'x 'x) is false. In CL, in the same package, (eq 'a 'a) is true. Some consequences: another feature is that Clojure's syntax-quote/quasi-quote ` for macros will automatically bring in the symbol's full namespace, e.g. if you (ns a) and quote 'inc or 'a you'll get inc and a back, but if you syntax-quote `inc and `a you'll get back clojure.core/inc and a/a respectively. This helps reduce the chance of name collisions. Another consequence is that since symbols don't belong to namespaces in Clojure, you don't have to worry about a CL behavior of polluting your package's namespace with a bunch of symbols. (i.e. in CL when you switch to package a and type 'a, you just interned the symbol a in that package.) And another consequence is that if you make a function private in Clojure, you can't get at it with the symbol name from outside of the namespace, whereas in CL, if you don't export something from your package (making it "private"), you can still get at it outside with package::symbol.