Oh gosh how could I neglect a mention of type_app, the type which represents function application itself? #include "node.h" #include "type_app.h" static

Oh gosh how could I neglect a mention of type_app, the type which represents function application itself? #include "node.h" #include "type_app.h" static struct node *reduce(struct node *parent) { struct node *curr = parent->LEFT; while (curr->type == parent->type) { struct node *self = curr->LEFT; struct node *next = self->type->reduce(curr); if (next != curr) { hold(next); drop(curr); curr = next; } } parent->LEFT = curr; return curr->type->reduce(parent); } static struct type type = { reduce, clear_pair }; struct node *make_app(struct node *f, struct node *x) { return make_pair(&type, f, x); } That "while" loop you see there is essentially the only loop in the entire core of Fexl. (Obviously "plug-ins" can do their own loops.) That loop keeps reducing the parent node as long as it's still of type_app. Then the loop ends and it reduces whatever the parent node has become as a result of the evaluation loop.