Dyalog User Commands: Difference between revisions

User commands are useful for the Dyalog  APL developer. Dyalog comes with a rich set of user commands, but independent parties also develop and maintain user commands. This article discusses how and where to install third-party user commands, and how to load them into <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight>.

Dyalog installs its own set of user commands into <syntaxhighlight lang=apl inline>[DYALOG]/SALT/spice</syntaxhighlight>. Installing third-party user commands into this folder has advantages and disadvantages.

* The user commands cannot be changed by an ordinary user (admin rights are required for that)

But what some may consider an advantage can also be viewed as a disadvantage. Installing it into a different place, the folder <syntaxhighlight lang=apl inline>MyUCMDs/</syntaxhighlight> (we discuss in a second where that folder lives), has some advantages:

* The user has "write" permission to that folder, so updating is easy

Like the <syntaxhighlight lang=apl inline>SALT/spice</syntaxhighlight> folder, <syntaxhighlight lang=apl inline>MyUCMDs/</syntaxhighlight> is scanned for user command scripts at startup time.

== Where does the folder MyUCMDs/ live? ==

The answer to this question depends on the operating system used.

* Under Windows it's usually <syntaxhighlight lang=apl inline>C:\Users\<username>\Documents\</syntaxhighlight>

* Under Linux and Mac OS it is <syntaxhighlight lang=apl inline>/home/<username>/</syntaxhighlight>

Note that this folder is created by the Dyalog APL installer under Windows but it won't exist under Linux and Mac OS in versions before 19.0, so you need to create the folder yourself on non-Windows platforms.

If you have Tatin installed, or you are using version 19.0 or later (those come with Tatin automatically) then you can call this Tatin API function:

       ⎕se.Tatin.GetMyUCMDsFolder'foo'

C:\Users\kai\Documents\MyUCMDs

Once a user command script is moved into a <syntaxhighlight lang=apl inline>MyUCMDs/</syntaxhighlight> folder (or a sub-folder of it) the user command will be available from any version of APL.

And that could be the end of the story in case the user command you want to install is relatively simple, so all the code can go into the script.

It's a different story when the user command relies on, say, a large set of code files that need to be loaded into <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight> in order to execute the user command.  

Now of course the user command script could check whether the code is already available in <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight> and if not do the loading, and that would work just fine.

However, these days it is becoming increasingly popular to add an API to a user command.

 

For example, the Dyalog APL project manager [Cider](https://github.com/aplteam/Cider) comes with a rich set of user commands:

But Cider also offers a public interface:

If you want to use any of these API functions without the need of first calling any of the Cider user commands (that would allow the user command script to load the code into <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight>), then you have to make sure that the code is loaded, ideally at a very early stage: as part of the instantiating process.

== setup.dyalog in MyUCMDs/ ==

We are going to introduce a script <syntaxhighlight lang=apl inline>setup.dyalog</syntaxhighlight> into the folder <syntaxhighlight lang=apl inline>MyUCMDs/</syntaxhighlight>. We are doing this because when Dyalog finds such a script then it will check whether it has a function <syntaxhighlight lang=apl inline>Setup</syntaxhighlight>. If so then this function will be executed.

* The name of the script must be lowercase because otherwise it won't be found on non-Windows platforms

* The function <syntaxhighlight lang=apl inline>Setup</syntaxhighlight> must accept a right argument

Note that this also checks the version of Dyalog APL and whether it's "Classic" or not. Amend this to your needs.

Copy the functions <syntaxhighlight lang=apl inline>IfAtLeastVersion</syntaxhighlight>, <syntaxhighlight lang=apl inline>GetMyUCMDsFolder</syntaxhighlight> and </syntaxhighlight>LoadMyUserCommand</syntaxhighlight> from above into your own <syntaxhighlight lang=apl inline>setup.dyalog</syntaxhighlight> script and then make sure that <syntaxhighlight lang=apl inline>LoadMyUserCommand</syntaxhighlight> is called from your </syntaxhighlight>Setup</syntaxhighlight> function.

* There is no name specified after <syntaxhighlight lang=apl inline>[MyUCMDs]</syntaxhighlight> in the second argument of <syntaxhighlight lang=apl inline>InstallPackages</syntaxhighlight>: this makes the function act on the name of the package, here <syntaxhighlight lang=apl inline>MyUserCommand</syntaxhighlight>

* Usually <syntaxhighlight lang=apl inline>LoadDependencies</syntaxhighlight> loads packages into <syntaxhighlight lang=apl inline>#</syntaxhighlight> in case no second argument is specified, but because the folder was specified as an alias (<syntaxhighlight lang=apl inline>[MyUCMDs]</syntaxhighlight>) the function knows that this is about a user command, and therefore the default target for the load operation is <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight> and not <syntaxhighlight lang=apl inline>#</syntaxhighlight>.

* The user command script <syntaxhighlight lang=apl inline>MyUserCommand.dyalog</syntaxhighlight> is moved to the top of the folder hosting the user command, here <syntaxhighlight lang=apl inline>[MyUCMDs]/MyUserCommand</syntaxhighlight>

If you want to make sure that all user commands that are Tatin packages are loaded into <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight> at an early stage add this to your <syntaxhighlight lang=apl inline>setup.dyalog</syntaxhighlight> script and make sure that it is called by your <syntaxhighlight lang=apl inline>Setup</syntaxhighlight> function in that script:

  ⍝ This loads Tatin packages that are user commands installed in MyUCMDs/

           :If F.IsFile folder,'/apl-buildlist.json'

Note that it uses stuff from Tatin, so it works only with Tatin being available in <syntaxhighlight lang=apl inline>⎕SE</syntaxhighlight>, but since you are about to load Tatin packages that must be the case anyway.