PragPub 2011-07: Issue #25 by The Pragmatic Bookshelf

Author:The Pragmatic Bookshelf
Language: eng
Format: epub, mobi
Tags: PragPub—Monthly Magazine
Publisher: The Pragmatic Bookshelf, LLC
Published: 2011-07-01T04:00:00+00:00

user=> (second '(println "a"))

;=> "a"

This is a result of Lisp’s remarkable property of code being data.

A Little Closer to Clojure

Using the tick, we can get halfway to a DSL that looks like Clojure code.

(emit-bash-form

'(println "a"))

Let’s add this feature to emit-bash-form. We need to add a new clause to the case form. Which type should the dispatch value be?

user=> (class '(println "a"))

clojure.lang.PersistentList

So let’s add a clause for clojure.lang.PersistentList.

(defn emit-bash-form [a]

(case (class a)

clojure.lang.PersistentList

(case (name (first a))

"println" (str "echo " (second a))

nil)

java.lang.String a

java.lang.Integer (str a)

java.lang.Double (str a)

nil))

As long as we remember to quote the argument, this is not bad.

user=> (emit-bash-form '(println "a"))

"echo a"

user=> (emit-bash-form '(println "hello"))

"echo hello"

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