\DOC free_vars_lr
\TYPE {free_vars_lr : term -> term list}
\SYNOPSIS
Returns the set of free variables in a term, in order.
\KEYWORDS
variable, term.
\DESCRIBE
An invocation {free_vars_lr ty} returns a list representing the set of
type variables occurring in {ty}. The list will be in order of
variable occurrence when scanning the parse tree of the term from
left to right. This is usually, but need not be, the textual order when
the term is printed.
\FAILURE
Never fails.
\EXAMPLE
{
- free_vars_lr (Term `x /\ y /\ y ==> z`);
> val it = [`x`, `y`, `z`] : term list
}
\COMMENTS
{free_vars_lr} is not efficient for large terms with many free variables.
More strenuous applications should use high performance set
implementations
available in the Standard ML Basis Library.
\USES
{free_vars_lr} can be used to build pleasing quantifier prefixes.
\SEEALSO
Term.FVL, Term.free_vars, Term.empty_varset, Type.type_vars.
\ENDDOC