Action does not run without a leading !

action.notRun

Message

This <op> does not run: without a leading !, a top-level form is inert data, and <op> exists for its effect, so nothing happens at runtime. Prefix it with ! to run it.

What it means

MeTTa evaluates a top-level form only when it carries a leading !. Every other form is added to the space as data, which is exactly what you want for a fact or a rule.

It is not what you want for an op that exists for its effect. The standard library declares those with the unit return type (->): the assert family, add-atom, remove-atom, add-reduct, println!, print!. Such an op returns nothing a later query can match, so storing the call achieves nothing. The assertion never checks, the add-atom never adds, the println! never prints, and nothing reports it.

That silence is the danger. An unbanged assertEqualToResult in a test file looks exactly like a test that passes.

Why it happens

The ! is left off, or it ends up bound to something else. A bang binds to the next form across comments, so this runs:

;; check the retraction
!(assertEqualToResult (retract-source claim) (()))

but a second stray ! takes the bang for itself, leaving the assertion inert:

!;; check the retraction
!
(assertEqualToResult (retract-source claim) (()))   ; never runs

How to fix it

Add the leading ! so the form runs. The quick fix does this.

(assertEqual (+ 1 1) 2)    ; inert data — the assertion never checks
!(assertEqual (+ 1 1) 2)   ; runs — a failure is reported

An op you declare yourself is covered on the same footing, because the check reads the return type from the interpreter rather than from a list of builtin names:

(: log-fact (-> Atom (->)))
(log-fact (likes Sam pizza))    ; flagged: log-fact returns the unit type

A bare (import! …) has its own diagnostic, import.notRun, whose message names the module whose symbols stay undefined.

Controlled by the metta.diagnostics.actionNotRun setting.