1 files changed, 44 insertions, 5 deletions

diff --git a/src/reduce.c b/src/reduce.c
index 3fc7c48..07d1bfa 100644
--- a/src/reduce.c
+++ b/src/reduce.c
@@ -9,24 +9,63 @@
 #include <log.h>
 #include <assert.h>
 
-// only substitutes (and therefore rehashes) -> no explicit beta reduction
+static struct term *shift(struct term *term, size_t level, size_t amount)
+{
+	debug("shifting %lx\n", term->hash & HASH_MASK);
+	if (term->type == VAR) {
+		if (level > term->u.var.index)
+			return term;
+		struct term *rehashed =
+			term_rehash_var(term, term->u.var.index + amount);
+		return rehashed;
+	} else if (term->type == ABS) {
+		struct term *previous = term->u.abs.term;
+		struct term *new = shift(term->u.abs.term, level + 1, amount);
+		if (previous->hash == new->hash)
+			return term; // nothing changed
+		struct term *rehashed = term_rehash_abs(term, new);
+		/* term_rehash_parents(rehashed); */
+		/* if (rehashed->u.abs.term->hash == (*substitution)->hash) */
+		/* 	term_deref_head(previous, 1); */
+		return rehashed;
+	} else if (term->type == APP) {
+		hash_t previous_lhs = term->u.app.lhs->hash;
+		hash_t previous_rhs = term->u.app.rhs->hash;
+		struct term *lhs = shift(term->u.app.lhs, level, amount);
+		struct term *rhs = shift(term->u.app.rhs, level, amount);
+		if (previous_lhs == lhs->hash && previous_rhs == rhs->hash)
+			return term; // nothing changed
+		struct term *rehashed = term_rehash_app(term, lhs, rhs);
+		/* term_rehash_parents(rehashed); */
+		return rehashed;
+	}
+	fatal("invalid type %d\n", term->type);
+}
+
+// only substitutes (and therefore increments indices and rehashes)
 static struct term *substitute(struct term *term, struct term *substitution,
 			       size_t level)
 {
-	debug("substituting %lx with %lx\n", term->hash, substitution->hash);
+	debug("substituting %lx with %lx\n", term->hash & HASH_MASK,
+	      substitution->hash & HASH_MASK);
 	if (term->type == VAR) {
 		if (term->u.var.index == level) {
+			substitution->refs += 1; // TODO: Kinda hacky
+			shift(substitution, 0, level);
+			substitution->refs -= 1;
 			return substitution;
-		} else {
+		} else if (term->u.var.index < level) {
 			term_deref(substitution, 1);
 			return term;
+		} else {
+			fatal("implement\n");
 		}
 	} else if (term->type == ABS) {
 		struct term *previous = term->u.abs.term;
 		struct term *new =
 			substitute(term->u.abs.term, substitution, level + 1);
 		if (previous->hash == new->hash)
-			return new; // nothing changed
+			return term; // nothing changed
 		struct term *rehashed = term_rehash_abs(term, new);
 		term_rehash_parents(rehashed);
 		if (rehashed->u.abs.term->hash == substitution->hash)
@@ -55,7 +94,7 @@ struct term *reduce(struct term *term)
 	if (!term_is_beta_redex(term))
 		fatal("can't reduce non-beta-redex %d\n", term->type);
 
-	debug("reducing %lx\n", term->hash);
+	debug("reducing %lx\n", term->hash & HASH_MASK);
 
 	struct term *reduced = substitute(term->u.app.lhs, term->u.app.rhs, -1);
 	return reduced;