Clojure: High Performance JVM Programming

Reading and evaluating code

Let's have a look at how code can be parsed and evaluated in Clojure. The most elementary way to convert text into an expression is by using the read function. This function accepts a java.io.PushbackReader instance as its first argument, as shown here:

user> (read (-> "(list 1 2 3)"
                .toCharArray
                java.io.CharArrayReader.
                java.io.PushbackReader.))
(list 1 2 3)

Note

These examples can be found in src/m_clj/c4/read_and_eval.clj of the book's source code.

In this example, a string containing a valid expression is first converted into an instance of java.io.PushbackReader and then passed to the read function. It seems like a lot of unnecessary work to read a string, but it is due to the fact that the read function deals ...