pub fn free_vars(expr: &ast::Expr) -> HashSet<&str> {
    ast::visit_expr(FreeVarVisitor {
        free_set: HashSet::new(),
        block_bindings: vec![],
    }, expr).unwrap()
}
/// Compute the variables free in an expression given an initial set
/// of bindings.
Compute the variables free in an expression given an initial set
of bindings.
Compute the variables free in an expression given an initial set of bindings .
pub fn free_vars(expr: &ast::Expr) -> HashSet<&str> {
    ast::visit_expr(FreeVarVisitor {
        free_set: HashSet::new(),
        block_bindings: vec![],
    }, expr).unwrap()
}
pub fn free_vars ( expr : & ast :: Expr ) -> HashSet < & str > { ast :: visit_expr ( FreeVarVisitor { free_set : HashSet :: new ( ) , block_bindings : vec ! [ ] , } , expr ) . unwrap ( ) }
Compute the variables free in an expression given an initial set
of bindings.
Compute the variables free in an expression given an initial set of bindings .
expr
&ast::Expr