Free variable in a body

variable.undefined

Message

Undefined variable '<name>'.

What it means

A variable appears in a function body without being bound by the left side, a let, or a match. Off by default, since many MeTTa programs use free logic variables intentionally.

Why it happens

A typo in a variable name, or a variable that was meant to be bound by the pattern.

How to fix it

Bind the variable on the left side or in a let/match, or turn the check off if the free variable is intentional.

(= (f $x) (+ $x $y))   ; variable.undefined: $y is free

Controlled by the metta.diagnostics.undefinedVariables setting.