This article covers Chapter 10, Numbers, Characters, and Strings.
Lisp with Java guts
Because Clojure is Java under the covers, you can always use Java's support for numbers, characters, and strings. The Java interop syntax is clean and simple, so it is idiomatic to call Java directly, rather than write wrappers to make code look more Lisp-like. A few examples follow:
user=> (Math/pow 3 3) 27.0 user=> (.compareTo "a" "b") -1 user=> (Character/toLowerCase \A) \a
Numbers are numbers
In Clojure, as in most Lisps, numbers are numbers. They don't do irritating things like overflow:
user=> (* 1000000 1000000 1000000) 1000000000000000000
Also, integer division is exact:
user=> (/ 10 3) 10/3
Under the covers, Clojure's numeric representation switches Java types as necessary to do the right thing.
user=> (class (* 1000 1000)) java.lang.Integer user=> (class (* 1000000 1000000)) java.lang.Long user=> (class (* 1000000 1000000 1000000)) java.math.BigInteger
Study the API docs
Clojure does a good job of balancing the purity of math (Lisp) and the practical reality of efficient representation (Java's primitives). But you still have to know your way around. Some things are wrapped in Lisp, and some things aren't. For example, numbers support the mathematical comparison operators, but Strings use Java's
user=> (< 1 2) true user=> (< "a" "b") java.lang.ClassCastException: java.lang.String user=> (.compareTo "a" "b") -1 user=> (.compareTo 1 2) -1
If you aren't sure whether there is a Lispy wrapper for some functionality, you can check the API docs, or just try it in the REPL.
For numbers, characters, and strings, Clojure provides some of the trappings a Lisp programmer would expect, e.g. exact integer division. But under the covers, it's all Java. If you don't find what you need in the Clojure API, drop to Java using the interop syntax.
- The sample code is available at http://github.com/stuarthalloway/practical-cl-clojure.
- There is no sample code checked in for this chapter (Chapter 10). All the examples are one-liners that you can enter at the REPL.