Started reducer

has some problems still

1 files changed, 56 insertions, 0 deletions

diff --git a/src/reduce.c b/src/reduce.c
new file mode 100644
index 0000000..a927b12
--- /dev/null
+++ b/src/reduce.c
@@ -0,0 +1,56 @@
+// Copyright (c) 2023, Marvin Borner <dev@marvinborner.de>
+// SPDX-License-Identifier: MIT
+
+#include <stdio.h>
+
+#include <term.h>
+#include <reduce.h>
+#include <log.h>
+
+static struct term *substitute(struct term *term, struct term *substitution,
+			       size_t level)
+{
+	if (term->type == VAR && term->u.var.index == level) {
+		return substitution;
+	} else if (term->type == ABS) {
+		struct term *new =
+			substitute(term->u.abs.term, substitution, level + 1);
+		return term_rehash_abs(term, new);
+	} else if (term->type == APP) {
+		struct term *lhs =
+			substitute(term->u.app.lhs, substitution, level);
+		struct term *rhs =
+			substitute(term->u.app.rhs, substitution, level);
+		return term_rehash_app(term, lhs, rhs);
+	}
+	fatal("invalid type %d\n", term->type);
+}
+
+static struct term *reduce_app(struct term *term)
+{
+	if (term->u.app.lhs->type == ABS) {
+		return substitute(term->u.app.lhs->u.abs.term, term->u.app.rhs,
+				  0);
+	} else {
+		struct term *lhs = reduce(term->u.app.lhs);
+		struct term *rhs = reduce(term->u.app.rhs);
+		return term_rehash_app(term, lhs, rhs);
+	}
+}
+
+static struct term *reduce_abs(struct term *term)
+{
+	return reduce(term->u.abs.term);
+}
+
+struct term *reduce(struct term *term)
+{
+	if (term->type == APP) {
+		return reduce_app(term);
+	} else if (term->type == ABS) {
+		return reduce_abs(term);
+	} else if (term->type == VAR) {
+		return term;
+	}
+	fatal("invalid type %d\n", term->type);
+}