classes.tuple: document final class declaration

core/classes/tuple/tuple-docs.factor

@@ -191,6 +191,8 @@ $nl
     "tuple-inheritance-example"
     "tuple-inheritance-anti-example"
 } 
+"Declaring a tuple class final prohibits other classes from subclassing it:"
+{ $subsections POSTPONE: final }
 { $see-also "call-next-method" "parametrized-constructors" "unions" "mixins" } ;
 
 ARTICLE: "tuple-introspection" "Tuple introspection"
@@ -441,3 +443,6 @@ HELP: boa
 { $description "Creates a new instance of " { $snippet "class" } " and fill in the slots from the stack, with the top-most stack element being stored in the right-most slot." }
 { $notes "The name " { $snippet "boa" } " is shorthand for “by order of arguments”, and “BOA constructor” is a pun on “boa constrictor”." }
 { $errors "Throws an error if the slot values do not match class declarations on slots (see" { $link "tuple-declarations" } ")." } ;
+
+HELP: bad-superclass
+{ $error-description "Thrown if an attempt is made to subclass a class that is not a tuple class, or a tuple class declared " { $link POSTPONE: final } "." } ;

core/syntax/syntax-docs.factor

@@ -792,6 +792,10 @@ $nl
     { $code "TUPLE: person" "{ age integer initial: 0 }" "{ department string initial: \"Marketing\" }" "manager ;" }
 } ;
 
+HELP: final
+{ $syntax "TUPLE: ... ; final" }
+{ $description "Declares the most recently defined word as a final tuple class which cannot be subclassed. Attempting to subclass a final class raises a " { $link bad-superclass } " error." } ;
+
 HELP: initial:
 { $syntax "TUPLE: ... { slot initial: value } ... ;" }
 { $values { "slot" "a slot name" } { "value" "any literal" } }