ETscript

Why?

After spending a few years with JavaScript, I wanted to branch out into lower levels of programming. While researching starter projects I came across Robert Nystrom's wonderful book Crafting Interpreters, and writing an interpreter in C sounded like a good way to go about that. However, copy-pasting code as I read the book lulled me into a passive learning state where I wasn't retaining the material. I tried typing each line of code instead, thinking that would force me to pay attention, but that just ended up being tedious.

For the book's first half, using Python instead of Java helped me stay focused. I decided to take the same approach for the second half, but which alternative language should I use? Python didn't meet my lower-level goals. C++ seemed like a natural choice, but it was too difficult for me as a newcomer to quickly get up and running (I did eventually finish a PoC using C++ and plan to revisit it someday). Rust came up a lot during my search and not wanting to waste any more time, I thought, what the heck.

With an alternative host language selected, I began working through clox and started to wonder how the same techniques I was learning would apply to a different guest language. For whatever reason, a DSL I had used years ago when I was at ExactTarget/Salesforce named AMPscript came to mind. Many super frustrating months later, I ended up with ETscript.

To be clear, this is a personal hobby project without a real-world application. Salesforce doesn't offer a trial/developer account for their Marketing Cloud product (AMPscript's domain), so I had to rely on online resources and my fading memory of using it (I left in 2019). In other words, this is all experimental. Though only a subset of functions are implemented, anyone who doesn't have Marketing Cloud access should still be able to get a feel for AMPscript's syntax by using this.

Getting started

There isn't a fancy UI right now, so interaction takes place on the command line. Installing Docker then running it using the included shell scripts will be the fastest way to try things out.

After installing Docker, download ETscript's source code then change into the repo's directory:

$ git clone https://github.com/markgomez/etscript
$ cd etscript

Run the OS-appropriate script. For Linux and macOS:

$ ./dev

For Windows Terminal (recommended) or PowerShell 7:

> .\dev.ps1

When the Docker image finishes building, a command prompt similar to the following should appear after the container starts:

etscript@3a60ddb1e9b3:/workspace$

ETscript can be run in at least two ways. One way is interactively using the REPL:

# build and run
$ cargo run

ETscript 0.1.1 (press Control-C to quit)
>>> %%=Add(2, 2)=%%
4

Another way is to run your source code from a plain text file (recommended). Create a new file, hello.ets (filename extension doesn't matter), in the working directory then copy-paste the following code into it:

%%[
var @you
set @you = "world"
]%%
Hello, %%=v(@you)=%%!

Then pass the source file to the run command:

# build and run
$ cargo run hello.ets

Hello, world!

To leave the container and return to the host shell, press Control-D or type exit:

etscript@3a60ddb1e9b3:/workspace$ exit

If you prefer not to use Docker, you'll need to install and set up the latest versions of the following before running the cargo commands:

• Rust
• .NET SDK 8 (required for Native AOT)

Why is .NET being used in some parts?

Many of AMPscript's functions for handling dates or formatting numbers and strings expect .NET format specifiers. C#, along with external links to Microsoft's documentation, is referenced throughout AMPscript's own documentation. Date libraries are complicated things. I figured using date APIs that are native to .NET would be easier than trying to emulate them using time or chrono.

Are data extensions supported?

ETscript uses SQLite to emulate data extensions (tables). A table named _test_table is automatically created and can be used to try out the data extension functions. You can also create additional tables using your favorite SQL client, but you'll need to stick to the following expected typenames, some of which are custom^*:

Typename	Affinity
Integer	Integer
Real	Real
Boolean*	Numeric
DateTime*	Numeric
Text	Text

The database file, etscript.db, will be created (if it doesn't already exist) in the working directory (e.g., the repo's root).

A quick Lookup example:

%%[
UpsertData("_test_table", 1, "email", "[email protected]", "locale", "en-us")
]%%
Email: %%=Lookup("_test_table", "email", "locale", "en-us")=%%

$ cargo run hello.ets

Email: [email protected]

What's still being worked on?

• Attribute scope
• Garbage collection
• Testing
• Documentation