FML-script

FML-script (.fmlscript) is the other textual surface of the language, alongside FML proper. Where FML defines a model, FML-script drives it: it loads resources, creates instances, calls behaviours and checks values. It shares its expressions, its new and its types with FML proper — everything covered on the previous pages of this section works the same way inside a script — but its top level is a sequence of commands instead of a model { … } declaration.

Every example on this page and elsewhere in this section is itself a .fmlscript: the automated tests of the platform run them and check every assert.

Anatomy of a script

A script is a sequence of ;-terminated statements, with // line comments. A statement is a command, an FML expression, or an assignment (name = expr;):

virtualModel = load -r ["http://openflexo.org/test/TestResourceCenter/TaskList.fml"];
assert virtualModel != null;

service ResourceCenterService add_temp_rc;
list = new TaskList() with (name="groceries");
assert list.taskCount == 0;

milk = list.addTask("Buy milk");
assert milk.label == "Buy milk";

log "Test PASSED: the TaskList model of the user guide behaves as documented";

load -r […] loads a resource by address and gives the loaded object; for an .fml resource this is the virtual model itself. service ResourceCenterService add_temp_rc; gives the script a writable resource center, needed before creating any instance. new TaskList() with (name=…) instantiates the model; with (name=…) is mandatory, and omitting it stops the script with cannot instantiate … because new VirtualModelInstance name was not set. assert states a value that must hold: the run fails, with a message naming the line, if it does not.

Commands

Besides load and service, a script has a handful of directives for inspecting the runtime:

Command	Use
resources;	list the resources currently known
context;	print the bindings currently in scope
activate <adapter>;	activate a technology adapter
service <Name> <action> […];	drive a Flexo service (add_temp_rc, status…)
log <expr>;	write a message
assert <expr>;	check a value

Instantiating a model whose only creation scheme is named

new <Model>(…) reaches only an unnamed creation scheme. A model that declares only a named one must be instantiated by name:

public model Journal {

	String title;

	create::start(String title) {
		title = parameters.title;
	}

	public String label() {
		return title;
	}
}

diary = new Journal::start("Diary") with (name="diary");
assert diary != null;
assert diary.label() == "Diary";

new Journal() with (name="j1") on the same model does not resolve, and stops the script.

Querying from a script

select is an instruction of a behaviour body, not a script statement: select Task from vmi; on its own does not parse. To check what a query finds, call a behaviour that returns it, as the queries page does:

assert list.openTasks().size == 2;

Reserved words of a script

FML-script reserves its command names, on top of the reserved words of FML itself: help, history, execute, pwd, ls, cd, services, service, activate, resources, open, load, more, enter, exit, quit, context. A creation scheme named open fails to parse from a script (expecting: lidentifier), although the very same name parses fine inside FML proper: rename it if a script must instantiate it by name.

Known limits

• A failed load or new stops the script, with a message naming the failing command; nothing after it runs, unlike inside an FML behaviour where the same mistake often gives a silent null (see the expressions page).
• The whole script is checked before any command runs. An unresolved binding anywhere, even on the last line, aborts the run before the first line executes: none of the log lines are printed, however early they are. When a script does not print what you expect, look at its last lines first.
• Reassigning a name gives null from then on. x = "a"; x = "b"; leaves x at null, not "b", for every read after the second assignment — including further reassignments. Give every new value its own name instead of reusing one.

What you have seen

A script loads resources, instantiates models with new … with (name=…), and checks the result with assert. It shares FML's expressions and types, adds its own commands and reserved words, and fails a mistaken load or new outright rather than giving a silent null. Reassigning a name and querying without a behaviour are two things to avoid.

The models and scripts on this page (TaskList.fml, Journal.fml) are tests of the platform, in the openflexo-core repository.