From 90dc043368fd7245c6ad028a974b5b5ec3eebf5c Mon Sep 17 00:00:00 2001
From: Mart Lubbers <mart@martlubbers.net>
Date: Tue, 22 May 2018 12:39:28 +0200
Subject: [PATCH] add reference counter for future smarter allocations

---
 lambda.h |  1 +
 lambda.y |  6 ++++--
 mem.c    | 30 +++++++++++++++++-------------
 reduce.c | 20 ++++++++++----------
 reduce.h |  2 +-
 5 files changed, 33 insertions(+), 26 deletions(-)

diff --git a/lambda.h b/lambda.h
index ab28375..3eaa247 100644
--- a/lambda.h
+++ b/lambda.h
@@ -9,6 +9,7 @@
 enum lambda_which {lambda_ident, lambda_abs, lambda_app};
 struct lambda {
 	enum lambda_which which;
+	unsigned int refcount;
 	union {
 		struct {
 			char *ident;
diff --git a/lambda.y b/lambda.y
index 07c6b80..388693d 100644
--- a/lambda.y
+++ b/lambda.y
@@ -31,7 +31,9 @@ int yywrap()
 
 struct lambda *make_lambda()
 {
-	return malloc(sizeof (struct lambda));
+	struct lambda *t = malloc(sizeof (struct lambda));
+	t->refcount = 1;
+	return t;
 }
 
 struct lambda *make_ident(char *i)
@@ -119,7 +121,7 @@ lambda
 		{
 			int maxdepth = 1000;
 			printf("     ");
-			lambda_reduce($1, $1, &maxdepth);
+			lambda_reduce(&$1, &$1, &maxdepth);
 			lambda_print($1, NULL);
 			lambda_free($1);
 		}
diff --git a/mem.c b/mem.c
index 333038b..a0b18da 100644
--- a/mem.c
+++ b/mem.c
@@ -4,21 +4,25 @@
 void lambda_free(struct lambda *t)
 {
 	if(t != NULL){
-		switch(t->which){
-		case lambda_ident:
-			free(t->data.identifier.ident);
-			break;
-		case lambda_abs:
-			free(t->data.abstraction.ident);
-			lambda_free(t->data.abstraction.expr);
-			break;
-		case lambda_app:
-			lambda_free(t->data.application.expr1);
-			lambda_free(t->data.application.expr2);
-			break;
+		if(t->refcount == 1){
+			switch(t->which){
+			case lambda_ident:
+				free(t->data.identifier.ident);
+				break;
+			case lambda_abs:
+				free(t->data.abstraction.ident);
+				lambda_free(t->data.abstraction.expr);
+				break;
+			case lambda_app:
+				lambda_free(t->data.application.expr1);
+				lambda_free(t->data.application.expr2);
+				break;
+			}
+			free(t);
+		} else {
+			t->refcount--;
 		}
 	}
-	free(t);
 }
 
 struct lambda *copy(struct lambda *t)
diff --git a/reduce.c b/reduce.c
index 19c193c..b5e64e1 100644
--- a/reduce.c
+++ b/reduce.c
@@ -71,27 +71,27 @@ void lambda_beta(struct lambda *ident, struct lambda *body, struct lambda *targe
 	}
 }
 
-void lambda_reduce(struct lambda *t, struct lambda *total, int *maxdepth)
+void lambda_reduce(struct lambda **t, struct lambda **total, int *maxdepth)
 {
 	if(*maxdepth == 0)
 		return;
 	struct lambda *t1, *t2;
-	if(t->which == lambda_app){
-		t1 = t->data.application.expr1;
-		t2 = t->data.application.expr2;
-		lambda_reduce(t1, total, maxdepth);
+	if((*t)->which == lambda_app){
+		t1 = (*t)->data.application.expr1;
+		t2 = (*t)->data.application.expr2;
+		lambda_reduce(&t1, total, maxdepth);
 		if(t1->which == lambda_abs){
 			if(t1->data.abstraction.strict)
-				lambda_reduce(t2, total, maxdepth);
-			lambda_print(total, t);
+				lambda_reduce(&t2, total, maxdepth);
+			lambda_print(*total, *t);
 			printf("β -> ");
-			lambda_beta(t1, t1->data.abstraction.expr, t2, total);
+			lambda_beta(t1, t1->data.abstraction.expr, t2, *total);
 			lambda_free(t2);
 			t2 = copy(t1->data.abstraction.expr);
 			if(total == t)
-				*total = *t2;
+				**total = *t2;
 			lambda_free(t1);
-			*t = *t2;
+			**t = *t2;
 			free(t2);
 			(*maxdepth)--;
 			lambda_reduce(t, total, maxdepth);
diff --git a/reduce.h b/reduce.h
index 9d9fa54..833c7a9 100644
--- a/reduce.h
+++ b/reduce.h
@@ -3,5 +3,5 @@
 
 #include "lambda.h"
 
-void lambda_reduce(struct lambda *t, struct lambda *total, int *maxdepth);
+void lambda_reduce(struct lambda **t, struct lambda **total, int *maxdepth);
 #endif
-- 
2.20.1