Serving Lasso

There are lots of ways to create websites using Lasso. There are a number of frameworks available, plus other ones not listed on that page, that can help. You could even easily create your own framework. In this chapter, we will look at how easy it is to use files that embed Lasso in HTML code, and examine a simple packaging architecture that Lasso provides called LassoApps.

Embedding Lasso Code

Lasso is designed to make it easy to intermix HTML and Lasso code in a single file. Just create a normal HTML file with the “.lasso” extension and you can add Lasso code between the following delimiters: [ ... ], <?lasso ... ?>, or <?= ... ?>.

For example, you could place the following code in a file named “test.lasso” in the server’s web root:

   local(now) = date
<!DOCTYPE html>
   <title>Test Lasso</title>
      This page was loaded on [#now->format(`E, MMMM d, YYYY`)] at <?= #now->format(`h:mm:ss a`) ?>.
   It is currently
   [if(date->hour >= 5 and date->hour < 12) => {^]
   [else(date->hour >= 12 && date->hour < 17)]

Now all you need to do is use a web browser to request the URL from the server (e.g. and it will use Lasso to return an HTML page with something like the following content:

This page was loaded on Wed, July 31, 2013 at 10:36:42 AM
It is currently morning!

Creating LassoApps

A LassoApp is a bundle of Lasso source files, HTML files, images, and other media into a single deployable unit. While developing, this deployable unit is a folder with the above contents, but you can also choose to compile the bundle and have a binary file to distribute.

To create a LassoApp, create a directory in the “LassoApps” directory of your instance’s home directory. By default, URLs for the LassoApp will start with /lasso9/AppName/. The discussion that follows will assume an app named “AddressBook” with URLs that look like

Special Files

_install Files
The first time an instance loads a LassoApp, it will execute any files with a file name beginning with “_install” and ending with “.lasso” or “.inc”. For example, an install file that performs a specific task, such as creating a database required by the app, could be named “_install.create_dbs.lasso”.
_init File
Another special file is the “_init” file. While the “_install” files will only ever execute once at installation, a file such as “_init.lasso” will be executed every time the instance starts. Initialization files are used to define all of the types, traits, and methods used within the application; along with any code set by define_atBegin. (Defining methods, types, etc. is best done at startup on a production system, since redefining a method can have an impact on system resources.)

Matching URLs to Code Files

LassoApps match the code files they process based on the type of content requested as represented by the extension in the URL path. The default type is HTML if no extension is used or if the “.lasso” extension is used. That means the following example URLs will all match the same code:

Lasso matches those URLs to a file named “people.lasso” in the root of the AddressBook directory. It processes that file and then it checks for any secondary files to process. These secondary files are based on the content extension, so in the case of the above URLs, it will execute a file named “people[html].lasso”. The primary file can return a value that can be used by the secondary file. This allows you to easily separate code for logic from code for display. (Note that if you use the URL ending in “people.lasso”, Lasso won’t look for a secondary file to run based on content; only that code file will be run.)

For example, your “people.lasso” file could contain code to create an array of people objects and then return that array at the end:

local(found_people) = array

// ... populate the array ...

return #found_people

Your “people[html].lasso” file might look something like this:

   // Store the value returned from people.lasso
   local(contacts) = #1
<!DOCTYPE html>
   <title>Your Contacts</title>
      <tr><th>First Name</th><th>Middle Name</th><th>Last Name</th></tr>
   [with person in #contacts do {^]

This separation of logic and presentation allows for some rather powerful features. For example, let’s say we wanted our application to return a JSON representation of the array of people when accessed via the URL We already have the logic that finds the people and creates the array, so all that’s required is add a file named “people[xhr].lasso” to create and display the array of maps:

   local(people) = #1
      with person in #people
      select map(
         'firstName'  = #person->firstName,
         'middleName' = #person->middleName,
         'lastName'   = #person->lastName

For more information on creating and compiling LassoApps, see the LassoApps chapter.