Getting Started

In this application we will:

• define a list of products, stored in a dummy database,
• we’ll have an index page with a search form,
• we’ll display search results,
• and have one page per product to see it in details.

But everything starts with a project (a system in Lisp parlance) definition.

Setting up the project

Let’s create a regular Common Lisp project.

We could start straihgt from the REPL, but we’ll need a project definition to save our project dependencies, and other metadata. Such a project is an ASDF file.

Create the file myproject.asd at the project root:

(asdf:defsystem "myproject"
  :version "0.1"
  :author "me"
  :license "WTFPL"
  :depends-on (
               ;; web stack
               :hunchentoot  ;; web server
               :easy-routes  ;; routes facility
               :djula        ;; HTML templates
               )
  :components ((:module "src"  ;; a src/ subdirectory
                :components
                (
                 (:file "myproject") ;; = src/myproject.lisp
                )))

  :description "A list of products")

Now create a src/ subdirectory, in which you’ll create the one file mentioned in the .asd.

In src/myproject.lisp, add this:

(defpackage myproject
  (:use :cl))

(in-package :myproject)

;; Here our application code.

We created a Lisp package, a namespace if you want, and we made sure that the rest of our code will be written for this package. By default, we are in the cl-user package.

Sometimes the package definition is done in its own packages.lisp file: I like this approach for applications that grow.

we are now done with our project skeleton. Let’s compile and load our project and its dependencies.

Start your editor or a REPL.

Compile the .asd file with C-c C-k in Slime, or load it with (load "myproject.asd") from any REPL.

According you have installed Quicklisp, the library manager, quickload our system:

CL-USER> (ql:quickload "myproject")

To load "myproject":
  Load 1 ASDF system:
    myproject
; Loading "myproject"
..................................................
[package cl-syntax]...............................
[package cl-locale.core]..........................
[package cl-locale.reader]........................
[package cl-locale.syntax]........................
[package cl-locale]...............................
[package portable-pathnames]......................
[package djula]...................................
...

("myproject")

We are now ready to write the application logic.

A list of products

Our application will handle hundreds of thousands of products that it gets from a database. For now, we just want a dummy function to return us a list of products, so we can concentrate on the web stack.

We’ll write a function that returns n products. Each product is a list of three elements: the product id, its name and a price.

(in-package :myproject)

(defun products (&optional (n 5))
  (loop for i from 0 below n
        collect (list i
                      (format nil "Product nb ~a" i)
                      9.99)))

this returns:

((0 "Product nb 0" 9.99) (1 "Product nb 1" 9.99) (2 "Product nb 2" 9.99)
 (3 "Product nb 3" 9.99) (4 "Product nb 4" 9.99))

That’s not much, but that’s enough to show content in a web app, which we’ll do next.